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Welding Inspector

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Duties and Responsib i l i t ies

Sec t ion 1

Main Responsibilities 1.1

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• Code compliance

• Workmanship control

• Documentation control

Personal Attributes 1.1

Important qualities that good Inspectors are expected to have

are:•Honesty

•Integrity

•Knowledge

•Good communicator

•Physical fitness

•Good eyesight

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Standard for Visual Inspection 1.1

Basic Requirements

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BS EN 970 - Non-destructive examination of fusion

welds - Visual examination

Welding Inspection Personnel should:

• be familiar with relevant standards, rules and specifications

applicable to the fabrication work to be undertaken

• be informed about the welding procedures to be used

• have good vision (which shou ld be checked every 12

months)

Welding Inspection 1.2

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Conditions for Visual Inspection (to BS EN 970)

Illumination:

• 350 lux minimum required

• (recommends 500 lux - normal shop or office lighting)

Vision Access:

• eye should be within 600mm of the surface

• viewing angle (line from eye to surface) to be not less than

Aids to Visual Inspection (to BS EN 970)

When access is restricted may use:• a mirrored boroscope• a fibre optic viewing system

Other aids:• welding gauges (for checking bevel angles, weld profile, fillet

sizing, undercut depth)• dedicated weld-gap gauges and linear misalignment (high-low)

gauges

• straight edges and measuring tapes• magnifying lens (if magnification lens used it should have

magnification between X2 to X5)

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usually by

agreement

Welding Inspectors Equipment 1.3

Measuring devices:

• flexible tape, steel rule

• Temperature indicating crayons

• Welding gauges

• Voltmeter

• Ammeter

• Magnifying glass

• Torch / flash light• Gas flow-meter

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Welding Inspectors Gauges 1.3

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TWI Multi-purpose Welding Gauge Misalignment Gauges

Hi-Lo Gauge

Fillet Weld Gauges

G.A.L.

S.T.D.

G.A.L.

S.T.D.

01/4 1/2 3/4

I - L O

S i n g l e P u r p o s e W e l d i n g

G a u g e

Welding Inspectors Equipment 1.3

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Tong Tester

Ammeter Voltmeter

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Stages of Visual Inspection (to BS EN 970)Extent of examination and when required should be defined in

the application standard or by agreement between the

contracting parties

For high integrity fabrications inspection required throughout

the fabrication process:

Before welding

(Before assemble & After assembly)

During welding

After welding

Typical Duties of a Welding Inspector 1.5

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Before Welding

Preparation:

Familiarisation with relevant „documents‟…

• Application Standard/Code - for visual acceptance

requirements

• Drawings - item details and positions/tolerances etc

• Quality Control Procedures - for activities such as material

handling, documentation control, storage & issue of

welding consumables

• Quality Plan/Inspection & Test Plan/Inspection Checklist -

details of inspection requirements, inspection procedures

& records required

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Before WeldingWelding Procedures:

• are applicable to joints to be welded & approved

• are available to welders & inspectors

Welder Qualifications:

• list of available qualified welders related to WPS‟s

• certificates are valid and ‘in- date’

Before Welding

Equipment:• all inspection equipment is in good condition & calibrated as

necessary

• all safety requirements are understood & necessary equipment

availableMaterials:

• can be identified & related to test certificates, traceability !

• are of correct dimensions

• are in suitable condition (no damage/contamination)

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Before Welding

Consumables:

• in accordance with WPS’s

• are being controlled in accordance with Procedure

Weld Preparations:

• comply with WPS/drawing

• free from defects & contamination

Welding Equipment:

• in good order & calibrated as required by Procedure

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Before Welding

Fit-up

• complies with WPS

• Number / size of tack welds to Code / goodworkmanship

Pre-heat

• if specified• minimum temperature complies with WPS

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During Welding

Weather conditions

• suitable if site / field welding

Welding Process(es)

• in accordance with WPS

Welder

• is approved to weld the joint

Pre-heat (if required)

• minimum temperature as specified by WPS

• maximum interpass temperature as WPS

During Welding

Welding consumables

• in accordance with WPS

• in suitable condition

• controlled issue and handling

Welding Parameters

• current, voltage & travel speed – as WPS

Root runs

• if possible, visually inspect root before single-sided welds arefilled up

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During Welding

Inter-run cleaning

in accordance with an approved method (& back gouging) to

good workmanship standard

Distortion control

• welding is balanced & over-welding is avoided

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After Welding

Weld Identification

• identified/numbered as required

• is marked with welder‟s identity

Visual Inspection

• ensure weld is suitable for all NDT

• visually inspect & „sentence‟ to Code requirements

Dimensional Survey

• ensure dimensions comply with Code/drawing

Other NDT

• ensure all NDT is completed & reports available

After Welding

Repairs• monitor repairs to ensure compliance with Procedure, ensure

NDT after repairs is completed

• PWHT

• monitor for compliance with Procedure

• check chart records confirm Procedure compliance

Pressure / Load Test

• ensure test equipment is suitably calibrated

• monitor to ensure compliance with Procedure• ensure all records are available

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After WeldingDocumentation

• ensure any modifications are on ‘as-built’ drawings

• ensure all required documents are available

• Collate / file documents for manufacturing records

• Sign all documentation and forward it to QC department.

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Welding Inspector

Terms & Definitions

Section 2

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Welding Terminology & Definitions 2.1

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What is a Weld?• A localised coalescence of metals or non-metals produced

either by heating the materials to the welding temperature,

with or without the application of pressure, or by the

application of pressure alone (AWS)

• A permanent union between materials caused by heat, and

or pressure (BS499)

• An Autogenous weld:

A weld made with out the use of a filler material and canonly be made by TIG or Oxy-Gas Welding

Welding Terminology & Definitions 2.1

What is a Joint?

• The junction of members or the edges of members that areto be joined or have been joined (AWS)

• A configuration of members (BS499)

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Joint Terminology 2.2

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Edge Open & Closed Corner Lap

Tee ButtCruciform

Welded Butt Joints 2.2

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A_________Welded butt jointButt

A_________Welded butt jointFillet

A____________Welded butt jointCompound

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Welded Tee Joints 2.2

A_________Welded T jointFillet

A_________Welded T jointButt

A____________Welded T jointCompound

Weld Terminology 2.3

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Compound weld

Fillet weldButt weld

Edge weld

Spot weld

Plug weld

B tt P ti Si

Butt Preparations – Sizes 2.4

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Full Penetration Butt Weld

Partial Penetration Butt Weld

Design Throat

Thickness

Design Throat

Thickness

Actual Throat

Thickness

Actual Throat

Thickness

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Weld Zone Terminology 2.5

WeldBoundary

HeatAffectedZone

Weldmetal

A, B, C & D = Weld Toes

W ld Z T i l

Weld Zone Terminology 2.5

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Excess RootPenetration

ExcessCap height

or WeldReinforcement

Weld cap width

Design

ThroatThickness

Actual Throat

Thickness

H Aff d Z (HAZ)

Heat Affected Zone (HAZ) 2.5

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tempered zone

grain growth zone

recrystallised zone

partially transformed zone

Maximum

Temperature

solid-liquid Boundarysolid

unaffected base

material

Joint Preparation Terminology 2.7

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Included angle

Root GapRoot Face

Angle of

Root FaceRoot Gap

Included angle

RootRadius

Single-V Butt Single-U Butt

J i t P ti T i l

Joint Preparation Terminology 2.8 & 2.9

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Root Gap

Root Face Root FaceRoot Gap

Radius

Single Bevel Butt Single-J Butt

Angle of bevel Angle of bevel

Si l Sid d B P i

Single Sided Butt Preparations 2.10

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Single Bevel Single Vee

Single-J Single-U

Single sided preparations are normally made on thinner materials, or

when access form both sides is restricted

Double Sided Butt Preparations

Double Sided Butt Preparations 2.11

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Double sided preparations are normally made on thicker materials, or

when access form both sides is unrestricted

-VeeDouble-BevelDouble

- JDouble - UDouble

Weld Preparation

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Terminology & Typical Dimensions: V-Joints

bevel angle

root face

root gap

included angle

Typical Dimensions

bevel angle 30 to 35°

root face ~1.5 to ~2.5mm

root gap ~2 to ~4mm

Butt Weld Toe Blend

Butt Weld - Toe Blend

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Poor Weld Toe Blend Angle

Improved Weld Toe Blend

•Most codes quote the weld

toes shall blend smoothly

•This statement is not

quantitative and therefore

open to individual

interpretation

•The higher the toe blend

angle the greater the

amount of stress

concentration•The toe blend angle ideally

should be between 20o-30o

Fillet Weld Features 2.13

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Design

Throat

Vertical

Length

Horizontal leg

Length

Excess

Fill t W ld Th t Thi k

Fillet Weld Throat Thickness 2.13

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b = Actual Throat Thickness

a = Design Throat Thickness

Deep Penetration Fillet Weld Features

Deep Penetration Fillet Weld Features 2.13

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b = Actual Throat Thickness

a = Design Throat Thickness

Fillet Weld Sizes

Fillet Weld Sizes 2.14

Calculating Throat Thickness from a known Leg Length:

Design Throat Thickness = Leg Length x 0.7

Question: The Leg length is 14mm.

What is the Design Throat?

Answer: 14mm x 0.7 = 10mm Throat Thickness

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Fillet Weld Sizes

Calculating Leg Length from a known Design Throat

Thickness:

Leg Length = Design Throat Thickness x 1.4

Question: The Design Throat is 10mm.

What is the Leg length?

Answer: 10mm x 1.4 = 14mm Leg Length

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Features to Consider 2

Features to Consider 2 2.14

Importance of Fillet Weld Leg Length Size

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Approximately the same weld volume in both Fillet

Welds, but the effective throat thickness has been

altered, reducing considerably the strength of weld B

Fillet Weld Sizes

Importance of Fillet weld leg length Size

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Area = 4 x 4 =

Area = 6 x 6 =

The c.s.a. of (b) is over double the area of (a) without the extra

excess weld metal being added

4mm 6mm

(a) (b)

4mm 6mm

(a) (b)

Excess

Fillet Weld Profiles

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Fillet Weld Profiles 2.15

Mitre Fillet Convex Fillet

Concave Fillet

A concave profile

is preferred for

joints subjected to

fatigue loading

Fi llet welds - Shape

Fillet Features to Consider

EFFECTIVE THROAT THICKNESS

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“s” = Effective throat thickness

“a” = Nominal throat thickness

Deep penetration fillet welds from high heat

input welding process MAG, FCAW & SAW etc

Fillet Features to Consider 2.15

ldi i i

Welding Positions 2.17

PA 1G / 1F Flat / Downhand

PB 2F Horizontal-Vertical

PC 2G Horizontal

PD 4F Horizontal-Vertical (Overhead)

PE 4G Overhead

PF 3G / 5G Vertical-Up

PG 3G / 5G Vertical-Down

H-L045 6G Inclined Pipe (Upwards)

J-L045 6G Inclined Pipe (Downwards)

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W ldi P i i

Welding Positions 2.17

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Welding position designation 2 17

Welding position designation 2.17

Butt welds in plate (see ISO 6947)

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Flat - PA Overhead - PE

Vertical

up - PF

Vertical

down - PG

Horizontal - PC

Butt welds in pipe (see ISO 6947)

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Flat - PA

axis: horizontalpipe: rotated

H-L045

axis: inclined at 45°

pipe: fixed

Horizontal - PC

axis: vertical

pipe: fixed

Vertical up - PF

axis: horizontal

pipe: fixed

Vertical down - PG

axis: horizontal

pipe: fixed

J-L045

axis: inclined at 45°

pipe: fixed

Fillet welds on plate (see ISO 6947)

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Flat - PA Overhead - PD

Vertical up - PF Vertical down - PG

Horizontal - PB

Fillet welds on pipe (see ISO 6947)

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Flat - PAaxis: inclined at 45°

pipe: rotated

Overhead - PDaxis: vertical

pipe: fixed

Vertical up - PFaxis: horizontal

pipe: fixed

Vertical down - PGaxis: horizontal

pipe: fixed

Horizontal - PBaxis: vertical

pipe: fixed

Horizontal - PBaxis: horizontal

pipe: rotated

Plate/Fillet Weld Positions

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Plate/Fillet Weld Positions 2.17

PA / 1GPA / 1F

PC / 2GPB / 2F

PD / 4FPE / 4G PG / 3G

PF / 3G

Pipe Welding Positions 2 17

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Pipe Welding Positions 2.17

Weld: Flat

Pipe: rotated

Axis: Horizontal

PA / 1G

Weld: Vertical Downwards

Pipe: Fixed

Axis: Horizontal

PG / 5G

Weld: Vertical upwards

Pipe: Fixed

Axis: Horizontal

PF / 5G

Weld: Upwards

Pipe: Fixed

Axis: Inclined

Weld: Horizontal

Pipe: Fixed

Axis: Vertical

PC / 2G

Weld: Downwards

Pipe: Fixed

Axis: Inclined

J-LO 45 / 6G

H-LO 45 / 6G

Travel Speed Measurement

Travel Speed Measurement 2.18

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Definition: the rate of weld progression

measured in case of mechanised and automaticwelding processes

in case of MMA can be determined using ROL and arc

Welding Inspector

Welding Imperfections

Section 3

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Welding Imperfections 3.1

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All welds have imperfections

• Imperfections are classed as defects when they are of a

type, or size, not allowed by the Acceptance Standard

A defect is an unacceptable imperfection

• A weld imperfection may be allowed by one Acceptance

Standard but be classed as a defect by another Standard

and require removal/rectification

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Standards for Welding Imperfections

BS EN ISO 6520-1(1998) Welding and allied processes –

Classification of geometric

imperfections in metallic materials -

Part 1: Fusion welding

Imperfections are classified into 6 groups, namely:

1 Cracks

2 Cavities

3 Solid inclusions

4 Lack of fusion and penetration

5 Imperfect shape and dimensions

6 Miscellaneous imperfections

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Standards for Welding Imperfections

EN ISO 5817 (2003) Welding - Fusion-welded joints in steel,

nickel, titanium and their alloys (beam

welding excluded) - Quality levels for

imperfections

This main imperfections given in EN ISO 6520-1 are listed inEN ISO 5817 with acceptance criteria at 3 levels, namely

Level B (highest)

Level C (intermediate)

Level D (general)

This Standard is „directly applicable to visual testing of welds‟

...(weld surfaces & macro exam inat ion)

Welding imperfections

Welding imperfections 3.1

classification

Cracks

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Cracks 3.1

Cracks

Cracks that may occur in welded materials are

caused generally by many factors and may beclassified by shape and position.

Note: Cracks are classed as Planar Defects.

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Classified by Shape

•Longitudinal

•Transverse•Chevron

•Lamellar Tear

Classified by Position

•HAZ

•Centerline•Crater

•Fusion zone

•Parent metal

Cracks

Cracks 3.1

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Longitudinal parent metal

Longitudinal weld metal

Lamellar tearing

Transverse weld metal

Cracks

Cracks 3.1

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Transverse crack Longitudinal crack

Cracks

Cracks 3.2

Main Crack Types

• Solidification Cracks

• Hydrogen Induced Cracks

• Lamellar Tearing

• Reheat cracks

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Cracks

Cracks 3.2

Solidification Cracking

• Occurs during weld solidification process

• Steels with high sulphur impurities content (low ductility

at elevated temperature)

• Requires high tensile stress

• Occur longitudinally down centre of weld

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Cracks 3.3

Hydrogen Induced Cold Cracking

• Requires susceptible hard grain structure, stress, low

temperature and hydrogen

• Hydrogen enters weld via welding arc mainly as result of

contaminated electrode or preparation

• Hydrogen diffuses out into parent metal on cooling

• Cracking developing most likely in HAZ

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Lamellar Tearing 3.5

g• Location: Parent metal

• Steel Type: Any steel type possible

• Susceptible Microstructure: Poor through thickness ductility

• Lamellar tearing has a step like appearance due to the solidinclusions in the parent material (e.g. sulphides and

silicates) linking up under the influence of welding stresses

• Low ductile materials in the short transverse directioncontaining high levels of impurities are very susceptible tolamellar tearing

• It forms when the welding stresses act in the shorttransverse direction of the material (through thicknessdirection)

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Gas Cavities

Gas Cavities 3.6

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Root piping

Cluster porosityGas pore

Blow hole

Herringbone porosity

Gas pore <1.5mm

Blow hole.>1.6mm

Causes:

•Loss of gas shield

•Damp electrodes

•Contamination

•Arc length too large•Damaged electrode flux

•Moisture on parent material

•Welding current too low

Gas Cavities

Gas Cavities 3.7

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Root pip ing

Porosi ty

Gas Cavities 3.8

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Cluster porosity Herringbone porosity

Crater Pipe

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Crater pipe

Weld crater

Crater Pipe 3.9

Crater Pipe

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Crater pipe is a shrinkage defect and not a gas defect, it has

the appearance of a gas pore in the weld crater

Causes:

• Too fast a cooling

• Deoxidization

reactions and

liquid to solid

volume change

• Contamination

Crater cracks

(Star cracks)

Crater pipe

Crater Pipe 3.9

Solid Inclusions 3 10

Solid Inclusions 3.10

Slag inclusions are defined as a non-metallic inclusion caused

by some welding process

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Causes:

•Slag originates from

welding flux

•MAG and TIG welding

process produce silicainclusions

•Slag is caused by

inadequate cleaning

•Other inclusions includetungsten and copper

inclusions from the TIG

and MAG welding process

Slag inclusions

Parallel slag lines

Lack of sidewallfusion with

associated slag

Lack of interun

fusion + slag

Solid Inclusions

Solid Inclusions 3.11

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Elongated slag linesInterpass slag inclusions

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Typical Causes of Lack of Fusion:

• welding current too low

• bevel angle too steep

• root face too large (single-sided weld)

• root gap too small (single-sided weld)• incorrect electrode angle

• linear misalignment

• welding speed too high

• welding process related – particularly dip-transfer GMAW

• flooding the joint with too much weld metal (blocking Out)

Lack of Fusion 3 13

Lack of Fusion 3.13

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Incomplete filled groove +

Lack of sidewall fusion

1. Lack of sidewall fusion

2. Lack of inter-run fusion

Causes:

•Poor welder skill

• Incorrect electrode

manipulation

• Arc blow

• Incorrect welding

current/voltage

• Incorrect travel speed

• Incorrect inter-run cleaning

Lack of Fusion 3 13

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Lack of sidewall fusion + incomplete filled groove

Lack of Fusion 3.13

Weld Root Imperfections 3.15

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Lack of Root FusionLack of Root Penetration

Undercut 3 18

Undercut 3.18

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Cap undercutRoot undercut

Surface and Profile 3 19

Surface and Profile 3.19

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Incomplete filled groove Poor cap profile

Excessive cap height

Poor cap profiles and

excessive cap reinforcements

may lead to stress

concentration points at the

weld toes and will alsocontribute to overall poor toe

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Incomplete filled grooveExcess cap reinforcement

Weld Root Imperfections 3 20

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Excessive root

penetration

Overlap 3 21

Overlap 3.21

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An imperfection at the toe or root of a weld caused by metal

flowing on to the surface of the parent metal without fusing to it

Causes:

•Contamination

•Slow travel speed

•Incorrect welding

technique

•Current too low

Overlap 3 21

Overlap 3.21

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Toe Overlap

Set-Up Irregularities 3.22

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Plate/pipe Linear Misalignment

(Hi-Lo)

Angular Misalignment

Linear misalignment is

measured from the lowest

plate to the highest point.

Angular misalignment is

measured in degrees

Set Up Irregularities 3.22

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Linear Misalignment

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Linear Misalignment

Incomplete Groove 3 23

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Lack of sidewall fusion + incomplete filled groove

Incomplete Groove 3.23

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Concave Root

Causes:

• Excessive back purge

pressure during TIG welding

Excessive root bead grindingbefore the application of the

second pass

welding current too high for

2nd pass overhead welding

root gap too large - excessive

„weaving‟

A shallow groove, which may occur in the root of a butt weld

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Concave Root

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Concave root Excess root penetration

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Causes:

• High Amps/volts

• Small Root face

• Large Root Gap

• Slow TravelSpeedBurn through

A localized collapse of the weld pool due to excessive

penetration resulting in a hole in the root run

Weld Root Imperfections 3 5

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Burn Through

Oxidized Root (Root Coking)

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Causes:

• Loss or insufficient

back purging gas (TIG)

• Most commonly occurs

when welding stainless

steels

• Purging gases includeargon, helium and

occasionally nitrogen

Miscellaneous Imperfections 3.26

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Arc strike

Causes:

• Accidental striking of the

arc onto the parent

material

• Faulty electrode holder

• Poor cable insulation

• Poor return lead

clamping

Miscellaneous Imperfections 3.27

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Causes:• Excessive current

• Damp electrodes

• Contamination

• Incorrect wire feed

speed when welding

with the MAG welding

process

• Arc blowSpatter

Mechanical Damage 3.28

Mechanical damage can be defined as any surface material

damage cause during the manufacturing process.

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• Grinding

• Hammering• Chiselling

• Chipping

• Breaking off welded attachments

(torn surfaces)

• Using needle guns to compress

weld capping runs

Welding Inspector

Destructive Testing

Section 4

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Qualitative and Quantitative Tests 4.1

The following mechanical tests have units and are termed

quantitative tests to measure Mechanical Properties• Tensile tests (Transverse Welded Joint, All Weld Metal)

• Toughness testing (Charpy, Izod, CTOD)

• Hardness tests (Brinell, Rockwell, Vickers)

The following mechanical tests have no units and are termed

qualitative tests for assessing joint quality

• Macro testing

• Bend testing

• Fillet weld fracture testing

• Butt weld nick-break testing

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Mechanical Test Samples 4.1

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Tensile Specimens

Fracture Fillet

Specimen

CTOD Specimen

Charpy Specimen

Bend Test

Specimen

Destructive Testing 4.1

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Typical Positions for Test

Pieces

Specimen Type Position

•Macro + Hardness 5

•Transverse Tensile 2, 4

•Bend Tests 2, 4

•Charpy Impact Tests 3

•Additional Tests 3

WELDING PROCEDURE QUALIFICATION TESTING

top of fixed pipe

Definitions

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• Malleability

• Ductility• Toughness

• Hardness

• Tensile Strength

Ability of a material to

withstand deformation

under static compressive

loading without rupture

Mechanical Properties of metals are related to the amount ofdeformation which metals can withstand under different

circumstances of force application.

Definitions

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• Malleability

• Hardness

Ability of a material

undergo plastic

deformation under static

tensile loading without

rupture. Measurable

elongation and reduction

in cross section area

Mechanical Properties of metals are related to the amount of

deformation which metals can withstand under different

Definitions

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• Malleability

• Hardness

Ability of a material to

withstand bending or the

application of shear

stresses by impact loading

without fracture.

Definitions

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• Malleability

• Hardness

Measurement of a

materials surface

resistance to indentationfrom another material by

static load

Definitions

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• Malleability

• Hardness

Measurement of the

maximum force required to

fracture a materials bar ofunit cross-sectional area in

tension

Transverse Joint Tensile Test 4.2

Weld on plate

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Multiple cross joint

specimensWeld on pipe

Tensile Test 4.3

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All-Weld Metal Tensile

Specimen

Transverse Tensile

Specimen

STRA (Short Transverse Reduction Area)

For materials that may be subject to Lamellar Tearing

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UTS Tensile test 4.4

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Charpy V-Notch Impact Test 4.5

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Objectives:

• measuring impact strength in different weld joint areas

• assessing resistance toward brittle fracture

Information to be supplied on the test report:

• Material type

• Notch type

• Specimen size

• Test temperature• Notch location

• Impact Strength Value

Ductile / Brittle Transition Curve 4.6

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- 50 0- 20 - 10- 40 - 30

Ductile fracture

Ductile/Brittletransitionpoint

47 Joules

28 Joules

Testing temperature - Degrees Centigrade

Temperature range

Transition range

Brittle fracture

Three specimens are normally tested at each temperature

Energy absorbed

Comparison Charpy Impact Test Results 4.6

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Impact Energy Joules

Room Temperature -20oC Temperature

1. 197 Joules

2. 191 Joules3. 186 Joules

1. 49 Joules

2. 53 Joules3. 51 Joules

Average = 191 Joules Average = 51 Joules

The test results show the specimens carried out at room

temperature absorb more energy than the specimens carried

out at -20oC

Charpy V-notch impact test specimen 4.7

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Specimen dimensions according ASTM E23

ASTM: American Society of Testing Materials

Charpy V-Notch Impact Test 4.8

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Specimen

Pendulum

(striker)

Anvil (support)

Charpy Impact Test 4.9

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Machined

100% DuctileMachined

Large reductionin area, shear

Fracture surface

100% bright

crystalline brittle

fracture

Randomly torn,

dull gray fracture

surface

100% Brittle

Hardness Testing 4.10

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Definition

Measurement of resistance of a material against

penetration of an indenter under a constant load

There is a direct correlation between UTS and

hardness

Hardness tests:

Brinell

Vickers

Rockwell

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Objectives:

• measuring hardness in different areas of a welded joint

• assessing resistance toward brittle fracture, cold cracking

and corrosion sensitivity within a H2S (Hydrogen Sulphide)

environment.

Information to be supplied on the test report:

• material type

• location of indentation

• type of hardness test and load applied on the indenter

• hardness value

Vickers Hardness Test 4.11

Vickers hardness tests:

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Vickers hardness tests:

indentation body is a square based diamond pyramid

(136º included angle)

the average diagonal (d) of the impression is

converted to a hardness number from a table

it is measured in HV5, HV10 or HV025AdjustableshuttersIndentationDiamond

indentor

Vickers Hardness Test Machine 4.11

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Brinell Hardness Test 4.11

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• Hardened steel ball of given diameter is subjected for

a given time to a given load• Load divided by area of indentation gives Brinell

hardness in kg/mm2

• More suitable for on site hardness testing

Ø=10mm

steel ball

Rockwell Hardness Test

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Ø=1.6mm

steel ball

Rockwell B Rockwell C

120 Diamond

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Hardness Test Methods Typical Designations

Vickers 240 HV10

Rockwell Rc 22

Brinell 200 BHN-W

usually the hardest region

1.5 to 3mm

fusion line

fusion

boundary

Hardness specimens can also be used for CTOD samples

Crack Tip Opening Displacement testing 4.12

p p g p g

• Test is for fracture toughness• Square bar machined with a notch placed in

the centre.

• Tested below ambient temperature at aspecified temperature.

• Load is applied at either end of the testspecimen in an attempt to open a crack at the

bottom of the notch

• Normally 3 samples

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Fatigue Fracture 4.13

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Location: Any stress concentration area

Steel Type: All steel types

Susceptible Microstructure: All grain structures

Test for Fracture Toughness is CTOD

(Crack Tip Opening Displacement)

Fatigue Fracture 4.13

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• Fatigue cracks occur under cyclic stress conditions

• Fracture normally occurs at a change in section, notchand weld defects i.e stress concentration area

• All materials are susceptible to fatigue cracking

• Fatigue cracking starts at a specific point referred to asa initiation point

• The fracture surface is smooth in appearance

sometimes displaying beach markings

• The final mode of failure may be brittle or ductile or a

combination of both

Fatigue Fracture

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• Toe grinding, profile grinding.

• The elimination of poor profiles

• The elimination of partial penetration welds and weld

defects

• Operating conditions under the materials endurance limits

• The elimination of notch effects e.g. mechanical damage

cap/root undercut

• The selection of the correct material for the service

conditions of the component

Precautions against Fatigue Cracks

Fatigue Fracture

Fatigue fracture occurs in structures subject to repeated

application of tensile stress.

Crack growth is slow (in same cases, crack may grow into an

area of low stress and stop without failure).

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Fatigue Fracture

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Initiation points / weld defects

Fatigue fracture surface

smooth in appearance

Secondary mode of failure

ductile fracture rough fibrous

appearance

Fatigue FractureF ti f t di ti i h f t

• Crack growth is slow• It initiate from stress concentration points

• load is considerably below the design or yield stress level

• The surface is smooth

• The surface is bounded by a curve

• Bands may sometimes be seen on the smooth surface –”beachmarks”.They show the progress of the crack front from the point of origin

• The surface is 90° to the load

• Final fracture will usually take the form of gross yielding (as themaximum stress in the remaining ligament increase!)

• Fatigue crack need initiation + propagation periods

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Fatigue fracture distinguish features:

Bend Tests 4.15

Object of test:

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• To determine the soundness of the weld zone. Bend

testing can also be used to give an assessment ofweld zone ductility.

• There are three ways to perform a bend test:

Root bend

Face bend

Side bend

Side bend tests are normally carried out on welds over 12mm in thickness

Bending test 4.16

Types of bend test for welds (acc. BS EN 910):

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Thickness of material - “t”

“t” up to 12 mm

“t” over 12 mm

Root / face

Side bend

Fillet Weld Fracture Tests 4.17

Object of test:

• To break open the joint through the weld to permitexamination of the fracture surfaces

• Specimens are cut to the required length

• A saw cut approximately 2mm in depth is applied alongthe fillet welds length

• Fracture is usually made by striking the specimen with asingle hammer blow

• Visual inspection for defects

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Fracture should break weld saw cut to root

Hammer

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This fracture indicates

lack of fusion

This fracture has

occurred saw cut to root

Lack of Penetration

Nick-Break Test 4.18

Object of test:

• To permit evaluation of any weld defects across the

fracture surface of a butt weld.

• Specimens are cut transverse to the weld

• A saw cut approximately 2mm in depth is applied along thewelds root and cap

• Fracture is usually made by striking the specimen with a

single hammer blow

•Visual inspection for defects

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Nick-Break Test 4.18

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Approximately 230 mm

Notch cut by hacksaw

Weld reinforcement

may or may not be

removed

Nick Break Test 4.18

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Inclusions on fracture

lineLack of root penetration

or fusion

Alternative nick-break test

specimen, notch applied all

way around the specimen

Summary of Mechanical Testing 4.19

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We test welds to establish minimum levels of mechanical

properties, and soundness of the welded joint

We divide tests into Qualitative & Quantitative methods:

Qualitative: (Have no units/numbers)

For assessing joint quality

Macro tests

Bend tests

Fillet weld fracture tests

Butt Nick break tests

Quantitative: (Have units/numbers)

To measure mechanical properties

Hardness (VPN & BHN)

Toughness (Joules & ft.lbs)

Strength (N/mm2 & PSI, MPa)

Ductility / Elongation (E%)

Welding Inspector

WPS – Welder Qualifications

Section 5

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Welding Procedure Qualification 5.1

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Question:

What is the main reason for carrying out a Welding ProcedureQualification Test ?

(What is the test try ing to show ?)

Answer:

To show that the welded joint has the properties* that satisfythe design requirements (fit for purpose)

* properties

•mechanical properties are the main interest - always strength buttoughness & hardness may be important for some applications

•test also demonstrates that the weld can be made without defects

Welding Procedures 5.1

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Producing a welding procedure involves:

• Planning the tasks

• Collecting the data

• Writing a procedure for use of for trial

• Making a test welds

• Evaluating the results

• Approving the procedure

• Preparing the documentation

In most codes reference is made to how the procedure are to

b d i d d h h l f h d i

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be devised and whether approval of these procedures is

required.

The approach used for procedure approval depends on thecode:

Example codes:

• AWS D.1.1: Structural Steel Welding Code

• BS 2633: Class 1 welding of Steel Pipe Work• API 1104: Welding of Pipelines

• BS 4515: Welding of Pipelines over 7 Bar

Other codes may not specifically deal with the requirement of

a procedure but may contain information that may be used in

writing a weld procedure

• EN 1011Process of Arc Welding Steels

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The welding engineer writes qualified Welding Procedure

Specifications (WPS) for production welding

Production welding conditions must remain within the range of

qualification allowed by the WPQR

(acco rdin g to EN ISO 15614)

( d i t EN St d d )

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(accord ing to EN Stand ards)

welding conditions are called welding variables

welding variables are classified by the EN ISO Standard as:

•Essential variables

•Non-essential variables

•Additional variables

Note: addit ional var iables = ASME su pp lementary essent ia l

The range of qualification for production welding is based on

the limits that the EN ISO Standard specifies for essentialvariables*

( * and when appl icable - the addi t ional var iab les)

( d i t EN St d d )

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(accord ing to EN Standards)

WELDING ESSENTIAL VARIABLESQuestion:

Why are some welding variables classified as essential ?

Answer:

A variable, that if changed beyond certain limits (specified by

the Welding Standard) may have a significant effect on the

properties* of the joint

* part icular ly joint strength and duct i l i ty

( d i t EN St d d )

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SOME TYPICAL ESSENTIAL VARIABLES

• Welding Process

• Post Weld Heat Treatment (PWHT)

• Material Type

• Electrode Type, Filler Wire Type (Classification)• Material Thickness

• Polarity (AC, DC+ve / DC-ve)

• Pre-Heat Temperature

• Heat Input

• Welding Position

Components of a welding procedure

Parent material

• Type (Grouping)

• Thickness

• Diameter (Pipes)

• Surface condition)

Welding process• Type of process (MMA, MAG, TIG, SAW etc)

• Equipment parameters

• Amps, Volts, Travel speed

Welding Consumables

• Type of consumable/diameter of consumable

• Brand/classification

• Heat treatments/ storage

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C t f ldi d

Joint design•Edge preparation

•Root gap, root face

•Jigging and tacking

•Type of baking

Welding Position

•Location, shop or site

•Welding position e.g. 1G, 2G, 3G etc

•Any weather precaution

Thermal heat treatments

•Preheat, temps

•Post weld heat treatments e.g. stress relieving

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Object of a welding procedure test

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Object of a welding procedure test

To give maximum confidence that the welds mechanicaland metallurgical properties meet the requirements of the

applicable code/specification.

Each welding procedure will show a range to which the

procedure is approved (extent of approval)

If a customer queries the approval evidence can be

supplied to prove its validity

Welding Procedures

Summary of designations:

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Summary of designations:

pWPS: Preliminary Welding Procedure Specification

(Before procedure approval)

WPAR (WPQR): Welding Procedure Approval Record

(Welding procedure Qualification record)

WPS: Welding Procedure Specification

(After procedure approval)

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Example:

Welding

Procedure

Specif icat ion

Welder Qualification 5.4

Numerous codes and standards deal with welder qualification

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Numerous codes and standards deal with welder qualification,

e.g. BS EN 287.

• Once the content of the procedure is approved the next

stage is to approve the welders to the approved procedure.

• A welders test know as a Welders Qualif ication Test (WQT).

Object of a welding qualification test:

• To give maximum confidence that the welder meets the

quality requirements of the approved procedure (WPS).

• The test weld should be carried out on the same material and

same conditions as for the production welds.

Welder Qualification 5.4 & 5.5

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Question:What is the main reason for qualifying a welder ?

Answer:

To show that he has the skill to be able to make production

welds that are free from defects

Note: when welding in accordance with a Qual i f ied WPS

The elder is allo ed to make prod ction elds ithin the

(accord ing to EN 287 )

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The welder is allowed to make production welds within the

range of qualification shown on the Certificate

The range of qualification allowed for production welding isbased on the limits that the EN Standard specifies for the

welder qualification essential variables

A Certificate may be withdrawn by the Employer if there is

reason to doubt the ability of the welder, for example• a high repair rate

• not working in accordance with a qualified WPS

The qualification shall remain valid for 2 years provided there is certifiedconfirmation of welding to the WPS in that time.

A Welder‟s Qualification Certificate automatically expires if the welder has not

used the welding process for 6 months or longer.

Welding Engineer writes a preliminary Welding Procedure

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g g p y g

Specification (pWPS) for each test weld to be made

• A welder makes a test weld in accordance with the pWPS

• A welding inspector records all the welding conditions used

for the test weld (referred to as the „as-run‟ conditions)

An Independent Examin er/ Examining Bo dy/ Third Party

inspec to r may be reques ted to m on i to r the qual if icat ion

process

The finished test weld is subjected to NDT in accordance withthe methods specified by the EN ISO Standard - Visual, MT or

PT & RT or UT

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Test weld is subjected to destructive testing (tensile, bend,

macro)The Application Standard, or Client, may require additional

tests such as impact tests, hardness tests (and for some

materials - corrosion tests)

A Welding Procedure Qualification Record (WPQR) is preparedgiving details of: -

• The welding conditions used for the test weld

• Results of the NDT

• Results of the destructive tests

• The welding conditions that the test weld allows forproduction welding

The Third Party may be requested to sign the WPQR as a true

record

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An approved WPS should be available covering the range of

qualification required for the welder approval.

• The welder qualifies in accordance with an approved WPS

• A welding inspector monitors the welding to make sure that thewelder uses the conditions specified by the WPS

EN Welding Standard states that an Independent Examin er,

Examin ing Body or Th ird Par ty Inspector may be requ i red to

moni tor the qu ali f icat ion process

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The finished test weld is subjected to NDT by the methods

specified by the EN Standard - Visual, MT or PT & RT or UT

The test weld may need to be destructively tested - for certain

materials and/or welding processes specified by the EN

Standard or the Client Specification

• A Welder‟s Qualification Certificate is prepared showing the

conditions used for the test weld and the range of qualification

allowed by the EN Standard for production welding

• The Qualification Certificate is usually endorsed by a Third

Party Inspector as a true record of the test

Information that should be included on a welders test certificate are,

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Information that should be included on a welders test certificate are,

which the welder should have or have access to a copy of !

• Welders name and identification number

• Date of test and expiry date of certificate

• Standard/code e.g. BS EN 287

• Test piece details

• Welding process.

• Welding parameters, amps, volts• Consumables, flux type and filler classification details

• Sketch of run sequence

• Welding positions

• Joint configuration details

• Material type qualified, pipe diameter etc

• Test results, remarks

• Test location and witnessed by

• Extent (range) of approval

Welding Inspector

Materials InspectionSection 6

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Material InspectionOne of the most important items to consider is Traceability.

The materials are of little use if we can not, by use of an effective QAsystem trace them from specification and purchase order to finaldocumentation package handed over to the Client.

All materials arriving on site should be inspected for:

• Size / dimensions

• Condition

• Type / specification

In addition other elements may need to be considered depending onthe materials form or shape

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Pipe Inspection

We inspect the condition

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p(Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)

Specification

Weldedseam

Other checks may need to be made such as: distortion tolerance,number of plates and storage.

Plate Inspection

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(Corrosion, Mechanical damage, Laps, Bands &Laminations)

Specification

Other checks may need to be made such as: distortiontolerance, number of plates and storage.

Parent Material Imperfections

Mechanical damage Lap

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Lamination

Segregation line

Laminations are caused in the parent plate by the steel making

process, originating from ingot casting defects.

Segregation bands occur in the centre of the plate and are low

melting point impurities such as sulphur and phosphorous.

Laps are caused during rolling when overlapping metal does not

fuse to the base material.

Lapping

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Lamination

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Laminations

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Plate Lamination

Welding Inspector

Codes & StandardsSection 7

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Codes & Standards

The 3 agencies generally identified in a code or standard:

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The 3 agencies generally identified in a code or standard:

The customer, or client

The manufacturer, or contractor

The 3rd party inspection, or clients representative

Codes often do not contain all relevant data, but may

refer to other standards

Standard/Codes/Specifications

STANDARDS

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STANDARDS

SPECIFICATIONS CODES

Examples

plate, pipe

forgings, castings

valves

electrodes

Examples

pressure vessels

bridges

pipelines

Welding Inspector

Welding SymbolsSection 8

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Weld symbols on drawings

Advantages of symbolic representation:

• simple and quick plotting on the drawing• does not over-burden the drawing

• no need for additional view

•gives all necessary indications regarding the specific joint tobe obtained

Disadvantages of symbolic representation:

• used only for usual joints

• requires training for properly understanding of symbols

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Th b li i i l d

The symbolic representation includes:

• an arrow line

• a reference line

• an elementary symbol

The elementary symbol may be completed by:

• a supplementary symbol

• a means of showing dimensions

• some complementary indications

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Dimensions

Convention of dimensions

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In most standards the cross sectional dimensions are given to

the left side of the symbol, and all linear dimensions are give on

the right side

a = Design throat thickness

s = Depth of Penetration, Throat thicknessz = Leg length (min material thickness)

BS EN ISO 22553

AWS A2.4

•In a fillet weld, the size of the weld is the leg length

•In a butt weld, the size of the weld is based on the depth of the

joint preparation

A method of transferring information from the

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design office to the workshop is:

The above information does not tell us much about the wishes

of the designer. We obviously need some sort of code which

would be understood by everyone.

Most countries have their own standards for symbols.

Some of them are AWS A2.4 & BS EN 22553 (ISO 2553)

Please weld

Joints in drawings may be indicated:

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Joints in drawings may be indicated:

•by detailed sketches, showing every dimension

•by symbolic representation

Elementary Welding Symbols(BS EN ISO 22553 & AWS A2.4)

Convention of the elementary symbols:

Various categories of joints are characterised by an elementary symbol.

The vertical line in the symbols for a fillet weld, single/double bevel buttsand a J-butt welds must always be on the left side.

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Square edge

butt weld

Weld type Sketch Symbol

Single-v

butt weld

Elementary Welding Symbols

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Single-V butt

weld with broad

root face

Single

bevel butt

weldSingle bevel

butt weld with

broad rootface

Backing run

Elementary Welding Symbols

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Single-U

butt weld

Single-J

butt weld

Fillet weld

Surfacing

ISO 2553 / BS EN 22553

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Plug weld

Resistance spot weld

Resistance seam weld

Square Butt weld

Steep flanked

Single-V Butt

Surfacing

Arrow Line

(BS EN ISO 22553 & AWS A2.4):

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Convention of the arrow line:

• Shall touch the joint intersection

• Shall not be parallel to the drawing

• Shall point towards a single plate preparation (when onlyone plate has preparation)

(AWS A2.4)

Reference Line

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Convention of the reference line:

Shall touch the arrow line

Shall be parallel to the bottom of the drawing

ISO 2553 / BS EN 22553

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Arrow line

Reference lines

Arrow side

Other side Arrow side

Other side

ISO 2553 / BS EN 22553

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Single-V Butt flush cap Single-U Butt with sealing run

Single-V Butt with

permanent backing strip

Single-U Butt withremovable backing strip

ISO 2553 / BS EN 22553

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Single-bevel butt Double-bevel butt

Single-bevel butt Single-J butt

ISO 2553 / BS EN 22553

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Partial penetration single-V butt

„S‟ indicates the depth of penetration

ISO 2553 / BS EN 22553

a = Design throat thickness

D th f P t ti Th t

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s = Depth of Penetration, Throat

thickness

z = Leg length(min material thickness)

a = (0.7 x z)

4mm Design throat

6mm leg

6mm Actual throat

ISO 2553 / BS EN 22553

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Arrow side

ISO 2553 / BS EN 22553

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Other side

6mm fillet weld

ISO 2553 / BS EN 22553

n = number of weld elements

l h f h ld l

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l = length of each weld element

(e ) = distance between each weld element

n x l (e )

Welds to bestaggered

Process

2 x 40 (50)

3 x 40 (50)111

ISO 2553 / BS EN 22553

All dimensions in mm

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80 80 80

909090

3 x 80 (90)

ISO 2553 / BS EN 22553

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6 80 80 80

909090

3 x 80 (90)

Supplementary symbo ls (BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbols

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Concave or Convex

Toes to be ground smoothly

(BS EN only)Site Weld

Weld all round

pp y y

Supplementary information such as welding process, weld

profile, NDT and any special instructions

Supplementary symbols

(BS EN ISO 22553 & AWS A2.4)

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Further supplementary information, such as WPS number, or

NDT may be placed in the fish tail

Ground flush

Welding process

numerical BS EN

Removable

backing strip

Permanent

backing strip

Convention of supplementary symbolsSupplementary information such as welding process, weld profile,

NDT and any special instructions

ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

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ConvexMitre

Toesshall be

blended

Concave

ISO 2553 / BS EN 22553Complimentary Symbols

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Field weld (site weld)

The component requiresNDT inspection

Additional information,the reference document

is included in the box

Welding to be carried out

all round component

(peripheral weld)

ISO 2553 / BS EN 22553

Numerical Values for Welding Processes:

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111: MMA welding with covered electrode121: Sub-arc welding with wire electrode

131: MIG welding with inert gas shield

135: MAG welding with non-inert gas shield

136: Flux core arc welding

141: TIG welding

311: Oxy-acetylene welding

72: Electro-slag welding

15: Plasma arc welding

AWS A2.4 Welding Symbols

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AWS Welding Symbols

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1(1-1/8)

60o1/8

Depth of

Effective

Throat

Root Opening

Groove Angle

AWS Welding Symbols

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1(1-1/8)

60o1/8

GSFCAW

Welding Process

AWS Welding Symbols

Welds to bet d

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3 – 10

staggered

Process

AWS Welding Symbols

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1(1-1/8)

Sequence of

Operations

1st Operation

2nd Operation

3rd Operation

AWS Welding Symbols

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1(1-1/8)

Sequence of

Operations

AWS Welding Symbols

Dimensions- Leg Length

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6 leg on member A

6Member A

Member B

Welding Inspector

Intro To Welding ProcessesSection 9

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Welding ProcessesWelding is regarded as a joining process in which the work

pieces are in atomic contact

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Pressure welding

• Forge welding

• Friction welding

• Resistance Welding

Fusion welding

• Oxy-acetylene

• MMA (SMAW)

• MIG/MAG (GMAW)• TIG (GTAW)

• Sub-arc (SAW)

• Electro-slag (ESW)

• Laser Beam (LBW)

• Electron-Beam (EBW)

Cons tant Current Power Sou rce (Drooping Character ist ic)

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20 8040 60 130 140120100 180160 200

Normal Operating

Voltage Range

Large voltage variation, e.g. +

10v (due to changes in arc

length)

Small amperage changeresulting in virtually constant

current e.g. + 5A.

V o l t a g

Amperage

Required for: MMA, TIG, Plasma

arc and SAW > 1000 AMPS

O.C.V. Striking voltage (typical) forarc initiation

Monitoring Heat Input

• Heat Input:

The amount of heat generated in the

welding arc per unit length of weld.

Expressed in kilo Joules per millimetre

length of weld (kJ/mm).

Heat Input (kJ/mm)= Volts x Amps

Travel speed(mm/s) x 1000

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4/23/2007 228 of 691

Weld and weld pool temperatures

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• Monitoring Heat Input As Required by

• BS EN ISO 15614-1:2004

• In accordance with EN 1011-1:1998

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When impact requirements and/or hardness requirements are

specified impact test shall be taken from the weld in the highest

heat input position and hardness tests shall be taken from the

weld in the lowest heat input position in order to qualify for all

positions

Welding Inspector

MMA WeldingSection 10

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MMA - Principle of operation

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MMA welding

Main features:

• Shielding provided by decomposition of flux covering

• Electrode consumable

• Manual process

Welder controls:

• Arc length

• Angle of electrode

• Speed of travel

• Amperage settings

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Manual Metal Arc Basic Equipment

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Power source

Holding oven

Inverter power

source

Electrode holder

Power cablesWelding visorfilter glass

Return lead

Electrodes

Electrode

Control panel

(amps, volts)

MMA Welding Plant

Transformer:

• Changes mains supply voltage to a voltage suitable for welding

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• Changes mains supply voltage to a voltage suitable for welding.

Has no moving parts and is often termed static plant.

Rectifier:

• Changes a.c. to d.c., can be mechanically or statically achieved.

Generator:

• Produces welding current. The generator consists of an armaturerotating in a magnetic field, the armature must be rotated at a

constant speed either by a motor unit or, in the absence of

electrical power, by an internal combustion engine.

Inverter:

• An inverter changes d.c. to a.c. at a higher frequency.

MMA Welding VariablesVoltage

• The arc voltage in the MMA process is measured as close to

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the arc as possible. It is variable with a change in arc lengthO.C.V.

• The open circuit voltage is the voltage required to initiate, or

re-ignite the electrical arc and will change with the type of

electrode being used e.g 70-90 volts

Current

• The current used will be determined by the choice of

electrode, electrode diameter and material type and

thickness. Current has the most effect on penetration.

Polarity• Polarity is generally determined by operation and electrode

type e.g DC +ve, DC –ve or AC

O C V Striking voltage (typical) for arc

Constant Current Power Source(Drooping Characteristic)

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20 8040 60 130 140120100 180160 200

Normal Operating

Voltage Range

Large voltage variation, e.g. +

10v (due to changes in arc

length)

Small amperage change

resulting in virtually constant

current e.g. + 5A.

V o l t a g

Amperage

O.C.V. Striking voltage (typical) for arc

initiation

MMA welding parametersTravel speed

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Travelspeed

Too highToo low

•wide weld bead contour

•lack of penetration

•burn-through

•lack of root fusion

•incomplete root

penetration•undercut

•poor bead profile,

difficult slag removal

MMA welding parameters

Type of current:

• voltage drop in welding cables is lower with AC

• inductive looses can appear with AC if cables are coiled

• cheaper power source for AC

• no problems with arc blow with AC

• DC provides a more stable and easy to strike arc, especially

with low current, better positional weld, thin sheet applications

• welding with a short arc length (low arc voltage) is easier with

DC, better mechanical properties

• DC provides a smoother metal transfer, less spatter

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MMA welding parametersWelding current

approx. 35 A/mm of diameter

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– governed by thickness, type of joint and welding

position

Welding

current

Too highToo low

•poor starting

•slag inclusions

•weld bead contour too

high•lack of

fusion/penetration

•spatter

•excess

penetration

•undercut•burn-through

MMA welding parametersArc length = arc voltage

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voltage Too highToo low

•arc can be extinguished

•“stubbing”

•spatter

•porosity

•excesspenetration

•undercut

•burn-through

Polarity: DCEP generally gives deeper penetration

MMA - Troubleshooting

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MMA quality (left to right)current, arc length and travel speed normal;

current too low;

current too high;arc length too short;

arc length too long;

travel speed too slow;

travel speed too high

MMA electrode holder

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Collet or twist type“Tongs” type with

spring-loaded jaws

MMA Welding Consumables

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The three main electrode covering types used in MMA welding

• Cellulosic - deep penetration/fusion

• Rutile - general purpose

• Basic - low hydrogen

(Covered in more detail in Section 14)

MMA Covered Electrodes

Most welding defects in MMA are caused by a lack of welder

skill (not an easily controlled process), the incorrect settings

MMA welding typical defects

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of the equipment, or the incorrect use, and treatment ofelectrodes

Typical Welding Defects:

•Slag inclusions

•Arc strikes

•Porosity

•Undercut

•Shape defects (overlap, excessive root penetration, etc.)

Manual Metal Arc Welding (MMA)

Advantages:

• Field or shop use

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• Range of consumables• All positions

• Portable

• Simple equipment

Disadvantages:• High welder skill required

• High levels of fume

• Hydrogen control (flux)

• Stop/start problems

• Comparatively uneconomic when compared with someother processes i.e MAG, SAW and FCAW

Welding Inspector

TIG WeldingSection 11

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Tungsten Inert Gas WeldingThe TIG welding process was first developed in the USA

during the 2nd world war for the welding of aluminum alloys

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• The process uses a non-consumable tungsten electrode

• The process requires a high level of welder skill

• The process produces very high quality welds.

• The TIG process is considered as a slow process comparedto other arc welding processes

• The arc may be initiated by a high frequency to avoid scratch

starting, which could cause contamination of the tungsten

and weld

TIG - Principle of operation

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TIG Welding Variables

Voltage

The voltage of the TIG welding process is variable only by the

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type of gas being used, and changes in the arc length

Current

The current is adjusted proportionally to the tungsten

electrodes diameter being used. The higher the current thedeeper the penetration and fusion

Polarity

The polarity used for steels is always DC –ve as most of the

heat is concentrated at the +ve pole, this is required to keepthe tungsten electrode at the cool end of the arc. When

welding aluminium and its alloys AC current is used

Types of current• can be DCEN or DCEP

• DCEN gives deep penetrationDC

• requires special power source

• low frequency - up to 20 pulses/sec(thermal pulsing)

• better weld pool control

• weld pool partially solidifiesbetween pulses4/23/2007 256 of 691

Type of

welding

current

can be sine or square wave

requires a HF current (continuos

or periodical)

provide cleaning action

Pulsed

current

Choosing the proper electrodeCurrent type influence

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Electrode capacity

Current type & polarity

Heat balance

Oxide cleaning action

Penetration

DCEN DCEPAC (balanced)

70% at work

30% at electrode

50% at work

50% at electrode

35% at work

65% at electrode

Deep, narrow Medium Shallow, wide

No Yes - every half cycle Yes

Excellent

(e.g. 3,2 mm/400A)

(e.g. 3,2 mm/225A)

(e.g. 6,4 mm/120A)

ARC CHARACTERISTICSConstant Current/Amperage Characteristic

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Large change in voltage =Smaller change in amperage

Welding VoltageLarge arc gap

Small arc

TIG - arc initiation methods

Arc initiation

method

• simple method

• tungsten electrode is in contactwith the workpiece!

• high initial arc current due to theshort circuit

• impractical to set arc length inadvance

• electrode should tap theworkpiece - no scratch!

• ineffective in case of AC• used when a high quality is not

essential

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Lift arc HF start

need a HF generator (spark-

gap oscillator) that generates a

high voltage AC output (radio

frequency) costly

reliable method required on

both DC (for start) and AC (to

re-ignite the arc)

can be used remotely

HF produce interference

requires superior insulation

Pulsed current• usually peak current is 2-10 times

background current ( A )

current

Background

current

• useful on metals sensitive to high heatinput

• reduced distortions

• in case of dissimilar thicknesses equal

penetration can be achieved

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C u r r e n t

Average current

one set of variables can be used in all positionsused for bridging gaps in open root joints

require special power source

Choosing the proper electrode

Polarity Influence – cathodic cleaning effect

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Tungsten Electrodes

Old types: (Slightly Radioactive)

• Thoriated: DC electrode -ve - steels and most metals

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• 1% thoriated + tungsten for higher current values

• 2% thoriated for lower current values

• Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

• Cerium: DC electrode -ve - steels and most metals

• Lanthanum: AC - Aluminum alloys and magnesium

TIG torch set-up• Electrode extension

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Electrode

extension

Stickout 2-3 times

electrode

diameter

Electrode

extension

Low electron

emission

Unstable arc

Overheating

Tungsten

inclusions

Tungsten ElectrodesOld types: (Slightly Radioactive)

• Thoriated: DC electrode -ve - steels and most metals

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• 1% thoriated + tungsten for higher current values

• 2% thoriated for lower current values

• Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

• Cerium: DC electrode -ve - steels and most metals

• Lanthanum: AC - Aluminum alloys and magnesium

Tungsten electrode typesPure tungsten electrodes:

colour code - green

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no alloy additions

low current carrying capacity

maintains a clean balled end

can be used for AC welding of Al and Mg alloys

poor arc initiation and arc stability with AC compared

with other electrode types

used on less critical applications

low cost

Tungsten electrode typesThoriated tungsten electrodes:

l d ll / d/ i l t

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colour code - yellow/red/violet

20% higher current carrying capacity compared to

pure tungsten electrodes

longer life - greater resistance to contaminationthermionic - easy arc initiation, more stable arc

maintain a sharpened tip

recommended for DCEN, seldom used on AC(difficult to maintain a balled tip)

This slightly radioactive

Tungsten electrode typesCeriated tungsten electrodes:

l d ( AWS A 5 12)

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colour code - grey (orange acc. AWS A-5.12)

operate successfully with AC or DC

Ce not radioactive - replacement for thoriated types

Lanthaniated tungsten electrodes:

colour code - black/gold/blue

operating characteristics similar with ceriated

electrode

Tungsten electrode typesZirconiated tungsten electrodes:

colour code brown/white

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colour code - brown/white

operating characteristics fall between those of pure

and thoriated electrodes

retains a balled end during welding - good for ACwelding

high resistance to contamination

preferred for radiographic quality welds

Electrode tip for DCENPenetration

increase r

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Electrode tip prepared for low

current welding

Electrode tip prepared for high

current welding

Vertex

Increase

Bead width

increase

Decrease

2 - 2 , 5

t i m e s

e l e c

t r o d e d i a m e t e

Electrode tip for AC

DC -ve

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Electrode tip groundElectrode tip ground and

then conditioned

TIG Welding VariablesTungsten electrodes

The electrode diameter, type and vertex angle are all critical

factors considered as essential variables The vertex angle is

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factors considered as essential variables. The vertex angle isas shown

Vetex angle

Note: when welding

aluminium with ACcurrent, the tungsten end

is chamfered and forms a

ball end when welding

DC -ve

Note: too fine an angle will

promote melting of the

electrodes tip

Choosing the proper electrodeFactors to be considered:

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Unstable

Tungsten

inclusions

Welding

current

Electrode tip

not properly

heated

Excessive

melting or

volatilisation

Penetration

Shielding gas requirements

• Preflow andpostflow

Shielding gas flow

Welding current

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Preflow Postflow

Flow rate

too low

Flow rate

too high

TIG torch set-upElectrode extension

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Electrode

extension

Stickout 2-3 times

electrodediameter

Electrode

extension

Low electron

emission

Unstable arc

Overheating

Tungsten

inclusions

Tungsten Inclusion

May be caused by Thermal Shock of

heating to fast and small fragments

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A Tungsten Inclusion always shows up as

bright white on a radiograph

heating to fast and small fragmentsbreak off and enter the weld pool, so a

“slope up” device is normally fitted to

prevent this could be caused by touch

down also.

Most TIG sets these days have slope-up devices that brings the current to

the set level over a short period of

time so the tungsten is heated more

slowly and gently

Most welding defects with TIG are caused by a lack of welder

skill, or incorrect setting of the equipment. i.e. current, torch

manipulation, welding speed, gas flow rate, etc.

TIG typical defects

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• Tungsten inclusions (low skill or wrong vertex angle)

• Surface porosity (loss of gas shield mainly on site)

• Crater pipes (bad weld finish technique i.e. slope out)

• Oxidation of S/S weld bead, or root by poor gas cover

• Root concavity (excess purge pressure in pipe)

• Lack of penetration/fusion (widely on root runs)

Tungsten Inert Gas WeldingAdvantages

• High quality

Disadvantages

• High skill factor required

• High quality

• Good control

• All positions

• Lowest H2 process

• Minimal cleaning

• Autogenous welding

(No filler material)

• Can be automated

• High skill factor required

• Low deposition rate

• Small consumable range

• High protection required

• Complex equipment

• Low productivity

• High ozone levels +HF

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Welding Inspector

MIG/MAG Welding

MIG/MAG WeldingSection 12

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Gas Metal Arc WeldingThe MIG/MAG welding process was initially developed in the

USA in the late 1940s for the welding of aluminum alloys.

The latest EN Welding Standards now refer the process by the

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The latest EN Welding Standards now refer the process by theAmerican term GMAW (Gas Metal Arc Welding)

• The process uses a continuously fed wire electrode

• The weld pool is protected by a separately supplied

shielding gas

• The process is classified as a semi-automatic welding

process but may be fully automated

• The wire electrode can be either bare/solid wire or flux

cored hollow wire

MIG/MAG - Principle of operation

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MIG/MAG process variables• Welding current

• Polarity

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•Increasing welding current

•Increase in depth and width

•Increase in deposition rate

MIG/MAG process variables

• Arc voltage

• Travel speed

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•Increasing travel speed

•Reduced penetration and width, undercut

•Increasing arc voltage

•Reduced penetration, increased width•Excessive voltage can cause porosity,

spatter and undercut

Gas Metal Arc WeldingTypes of Shielding Gas

MIG (Metal Inert Gas)

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• Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni)

• Most common inert gas is Argon

• Argon + Helium used to give a „hotter‟ arc - better for thicker

joints and alloys with higher thermal conductivity

MIG/MAG shielding gases

A (A )

Ar Ar-He He CO2

Argon (Ar):

higher density than air; low thermal conductivity the archas a high energy inner cone; good wetting at the toes; lowionisation potential

Helium (He):

lower density than air; high thermal conductivity uniformlydistributed arc energy; parabolic profile; high ionisationpotential

Carbon Dioxide (CO2):

cheap; deep penetration profile; cannot support spraytransfer; poor wetting; high spatter

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MIG/MAG shielding gasesGases for dip transfer:

• CO2: carbon steels only: deep penetration; fast welding

speed; high spatter levels

• Ar + up to 25% CO2: carbon and low alloy steels: minimum

spatter; good wetting and bead contour

• 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimisesundercut; small HAZ

• Ar: Al, Mg, Cu, Ni and their alloys on thin sections

• Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thickersections (over 3 mm)

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MIG/MAG shielding gasesGases for spray transfer

• Ar + (5-18)% CO2: carbon steels: minimum spatter; good

wetting and bead contour

wetting and bead contour• Ar + 2% O2: low alloy steels: minimise undercut; provides

good toughness

• Ar + 2% O2 or CO2: stainless steels: improved arc stability;

provides good fusion

• Ar: Al, Mg, Cu, Ni, Ti and their alloys

• Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than

pure Ar to offset heat dissipation• Ar + (25-30)% N2: Cu alloys: greater heat input

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Gas Metal Arc WeldingTypes of Shielding Gas

MAG (Metal Active Gas)

• Active gases used are Oxygen and Carbon Dioxide

• Argon with a small % of active gas is required for all steels

(including stainless steels) to ensure a stable arc & good

droplet wetting into the weld pool

• Typical active gases are

Ar + 20% CO2 for C-Mn & low alloy steels

Ar + 2% O2 for stainless steels

100% CO2 can be used for C - steels4/23/2007 294 of 691

MIG/MAG Gas Metal Arc Welding

Electrode

orientation

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Penetration Deep Moderate Shallow

Excess weld metal Maximum Moderate Minimum

Undercut Severe Moderate Minimum

Electrode extension

•Increased extension

MIG / MAG - self-regulating arc

Stable condition Sudden change in gun position

Arc length L = 6,4 mm

Arc voltage = 24V

Welding current = 250A

WFS = 6,4 m/min

Arc length L‟ = 12,7 mm

Arc voltage = 29V

WFS = 6,4 m/min

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L19 mm

25 mmL‟

Melt off rate = 6,4 m/min Melt off rate = 5,6

Current (A)

V o l t a g e ( V )

MIG/MAG - self-regulating arcSudden change in gun position

Arc length L‟ = 12,7 mm

Arc voltage = 29V

WFS = 6,4 m/min

M lt ff t 5 6 / i

Re-established stable condition

Arc length L = 6,4 mm

Arc voltage = 24V

WFS = 6,4 m/min

M lt ff t 6 4 / i

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25 mmL‟

Melt off rate = 5,6 m/min

Current (A)

V o l t a g e ( V )

25 mmL

Melt off rate = 6,4 m/min

Terminating the arc

• Burnback time

– delayed current cut-off to prevent wire freeze

in the weld end crater

Crater fill

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in the weld end crater

– depends on WFS (set as short as possible!)

Contact tip

Workpiec

Burnback time 0.05 sec 0.10 sec 0.15 sec

8 mm3 mm

Current - 250A

Voltage - 27V

WFS - 7,8 m/min

Wire diam. - 1,2 mmShielding gas -

Ar+18%CO2

Insulatin

g slag

MIG/MAG - metal transfer modes

VoltageElectrode diameter = 1,2 mm

WFS = 8,3 m/min

Current = 295 AV lt 28V

Current/voltage conditions4/23/2007 301 of 691

Current

Dip transfer

transfer

Globular

transfer

Electrode diameter = 1,2 mm

WFS = 3,2 m/min

Current = 145 A

Voltage = 18-20V

Voltage = 28V

MIG/MAG-methods of metal transfer

Dip transfer

Transfer occur due to short circuits

between wire and weld pool, high

level of spatter, need inductancecontrol to limit current raise

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pcontrol to limit current raise

Can use pure CO2 or Ar- CO2

mixtures as shielding gas

Metal transfer occur when arc isextinguished

Requires low welding current/arc

voltage, a low heat input process.

Resulting in low residual stress

and distortion

Used for thin materials and all

position welds

MIG/MAG-methods of metal transferSpray transfer

Transfer occur due to pincheffect NO contact between wire

and weld pool!

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Requires argon-rich shieldinggas

Metal transfer occur in small

droplets, a large volume weldpool

Requires high weldingcurrent/arc voltage, a high heatinput process. Resulting in highresidual stress and distortion

Used for thick materials andflat/horizontal position welds

MIG/MAG-methods of metal transferPulsed transfer

Controlled metal transfer, one droplet per pulse,

No transfer between droplet and weld pool!

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Requires special power sources

Metal transfer occur in small droplets (diameter equal

to that of electrode)

Requires moderate welding current/arc voltage, a

reduced heat input . Resulting in smaller residual

stress and distortion compared to spray transfer

Pulse frequency controls the volume of weld pool,

used for root runs and out of position welds

MIG/MAG - metal transfer modes

Pulsed transfer

Controlled metal transfer. one dropletper pulse. NO transfer during

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pper pulse. NO transfer during

background current!

Requires special power sources

Metal transfer occur in small droplets(diameter equal to that of electrode)

Requires moderate welding current/arc voltage, reduced

heat input‟ smaller residual stress and distortions

compared to spray transfer

Pulse frequency controls the volume of weld pool, used

for root runs and out of position welds

MIG/MAG-methods of metal transfer

Globular transfer

Transfer occur due to gravity or

short circuits between drops andweld pool

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Requires CO2 shielding gas

Metal transfer occur in large drops

(diameter larger than that of

electrode) hence severe spatter Requires high welding current/arc

voltage, a high heat input process.

Resulting in high residual stress

and distortion

Non desired mode of transfer!

O.C.V. Arc Voltage

Flat or Constant Voltage Characteristic Used With

MIG/MAG, ESW & SAW < 1000 amps

Flat or Constant Voltage Characteristic

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Virtually no Change.

Voltage

100 200 300

Large Current Change

Small VoltageChange.

Amperage

MIG/MAG welding gun assembly

Contact

diffuser The Push-Pull gun

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Handle

nozzle

Trigger WFS remote

control

potentiometer

Union nut

Gas Metal Arc WeldingPROCESS CHARACTERISTICS

• Requires a constant voltage power source, gas supply, wire

feeder, welding torch/gun and „hose package‟

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• Wire is fed continuously through the conduit and is burnt-off

at a rate that maintains a constant arc length/arc voltage

• Wire feed speed is directly related to burn-off rate

• Wire burn-off rate is directly related to current

• When the welder holds the welding gun the process is said

to be a semi-automatic process

• The process can be mechanised and also automated

• In Europe the process is usually called MIG or MAG

Most welding imperfections in MIG/MAG are caused by lack of

welder skill, or incorrect settings of the equipment

•Worn contact tips will cause poor power pick up, or transfer

MIG/MAG typical defects

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•Bad power connections will cause a loss of voltage in the arc

•Silica inclusions (in Fe steels) due to poor inter-run cleaning

•Lack of fusion (primarily with dip transfer)

•Porosity (from loss of gas shield on site etc)

•Solidification problems (cracking, centerline pipes, crater

pipes) especially on deep narrow welds

WELDING PROCESS

Flux Core Arc Welding

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Flux Core Arc Welding

(Not In The Training Manual)

Flux cored arc welding

methods

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With gas

shielding -

“Outershield”

Without gas

shielding -

“Innershield”

With metal

powder -

“Metal core”

“Outershield” - principle of operation

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ARC CHARACTERISTICS

Constant Voltage Characteristic

Small change in voltage =large change in amperage

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g g p g

The selfadjusting arc.

Large arc gap

Small arc gap

Insulated extension nozzle

Current carrying guild tube

Flux core

Wire joint

Flux Core Arc Welding (FCAW)

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Flux cored hollow wire

Flux powder

Arc shield composed ofvaporized and slag formingcompounds

Metal droplets covered

with thin slag coating

Moltenweldpool

Solidified weldmetal and slag

Flux corewires

Flux cored arc weldingFCAW

methods

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With gas

shielding -

“Outershield”

Without gas

shielding -

“Innershield”

With metal

powder -

“Metal core”

With activegas shielding

With inert gasshielding (137)

FCAW - differences from MIG/MAG• usually operates in DCEP

but some “Innershield”wires operates in DCEN

• power sources need to bef l d h

more powerful due to thehigher currents

• doesn't work in deep

transfer mode• require knurled feed rolls

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“Innershield” wires use

a different type of

welding gun

Backhand (“drag”) technique

Advantages

preferred method for flat or horizontal position

slower progression of the weld

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deeper penetration

weld stays hot longer, easy to remove dissolved

gassesDisadvantages

produce a higher weld profile

difficult to follow the weld jointcan lead to burn-through on thin sheet plates

Forehand (“push”) techniqueAdvantages

preferred method for vertical up or overhead

positionarc is directed towards the unwelded joint , preheat

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arc is directed towards the unwelded joint , preheat

effect

easy to follow the weld joint and control the

penetrationDisadvantages

produce a low weld profile, with coarser ripples

fast weld progression, shallower depth of penetration

the amount of spatter can increase

FCAW advantages• less sensitive to lack of fusion

• requires smaller included angle compared to MMA

• high productivity

• all positional

• smooth bead surface, less danger of undercut

• basic types produce excellent toughness properties

• good control of the weld pool in positional welding especially

with rutile wires

• seamless wires have no torsional strain, twist free

• ease of varying the alloying constituents• no need for shielding gas

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FCAW disadvantages• limited to steels and Ni-base alloys

• slag covering must be removed

• FCAW wire is more expensive on a weight basis than solid

wires (exception: some high alloy steels)

• for gas shielded process, the gaseous shield may be

affected by winds and drafts

• more smoke and fumes are generated compared with

MIG/MAG

• in case of Innershield wires, it might be necessary to

break the wire for restart (due to the high amount of

insulating slag formed at the tip of the wire)

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Advantages:

1) Field or shop use

Disadvantages:

1) High skill factor 2) Sl i l i

FCAW advantages/disadvantages

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2) High productivity

3) All positional

4) Slag supports and

shapes the weld Bead

5) No need for shielding

2) Slag inclusions

3) Cored wire is

Expensive

4) High level of fume

(Inner-shield)

5) Limited to steels andnickel alloys

Welding Inspector

Submerged Arc Welding

Section 13

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• Submerged arc welding was developed in the Soviet Union

during the 2nd world war for the welding of thick section steel.

• The process is normally mechanized.

• The process uses amps in the range of 100 to over2000 which

Submerged Arc Welding Introduction

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• The process uses amps in the range of 100 to over2000, which

gives a very high current density in the wire producing deep

penetration and high dilution welds.

• A flux is supplied separately via a flux hopper in the form of eitherfused or agglomerated.

• The arc is not visible as it is submerged beneath the flux layer

and no eye protection is required.

SAW Principle of operation

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Principles of operationFactors that determine whether to use SAW chemical

composition and mechanical properties required for the weld

deposit

• thickness of base metal to be welded

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• joint accessibility

• position in which the weld is to be made

• frequency or volume of welding to be performed

SAW methods

Semiautomatic Mechanised Automatic

supply

Filler wire spool

Flux hopper

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Wire electrode

Slide rail

SAW process variables• welding current

• current type and polarity

• welding voltage• travel speed

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travel speed

• electrode size

• electrode extension

• width and depth of the layer of flux

SAW process variablesWelding current

•controls depth of penetration and the amount of

base metal melted & dilution

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SAW operating variablesCurrent type and polarity

•Usually DCEP, deep

penetration, better

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resistance to

porosity

•DCEN increase

deposition rate but

reduce penetration

(surfacing)

•AC used to avoidarc blow; can give

unstable arc

SAW Consumables(Covered in detail in Section 14)

Fused fluxes advantages:

•good chemical homogeneity

•easy removal of fines without affecting fluxcomposition

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•normally not hygroscopic & easy storage and handling

•readily recycled without significant change in particle

size or composition

Fused fluxes disadvantages:•difficult to add deoxidizers and ferro-alloys (due to

segregation or extremely high loss)

•high temperatures needed to melt ingredients limit the

range of flux compositions

SAW ConsumablesAgglomerated fluxes advantages:

• easy addition of deoxidizers and alloying elements

• usable with thicker layer of flux when welding

l id ifi i

4/23/2007 345 of 691

• colour identification

Agglomerated fluxes disadvantages:

• tendency to absorb moisture

• possible gas evolution from the molten slag leading to

porosity

• possible change in flux composition due to segregation orremoval of fine mesh particles

SAW equipmentPower sources can be:

• transformers for AC

• transformer-rectifiers for DC

St ti h t i ti b

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Static characteristic can be:

• Constant Voltage (flat) - most of the power sources

• Constant Current (drooping)

SAW equipmentConstant Voltage (Flat Characteristic) power sources:

• most commonly used supplies for SAW

• can be used for both semiautomatic and automatic welding

lf l ti

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• self-regulating arc

• simple wire feed speed control

• wire feed speed controls the current and power supplycontrols the voltage

• applications for DC are limited to 1000A due to severe arc

blow (also thin wires!)

ARC CHARACTERISTICS

Constant Voltage Characteristic

Small change in voltage =large change in amperage

Large arc gap

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The selfadjusting arc.

Large arc gap

Small arc gap

SAW equipmentConstant Current (Drooping Characteristic) power sources:

• Over 1000A - very fast speed required - control of burn off

rate and stick out length

• can be used for both semiautomatic and automatic welding

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• not self-regulating arc

• must be used with a voltage-sensing variable wire feed

speed control• more expensive due to more complex wire feed speed

control

• arc voltage depends upon wire feed speed whilst the power

source controls the current• cannot be used for high-speed welding of thin steel

SAW equipmentWelding heads can be mounted on a:

Tractor type carriage

• provides travel along straight orgently curved joints

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• can ride on tracks set up along the

joint (with grooved wheels) or on

the workpiece itself

• can use guide wheels as tracking

device

• due to their portability, are used in

field welding or where the piece

cannot be moved

Courtesy of ESAB AB

SAW operating variablesWelding current

•too high current: excessive excess weld metal

(waste of electrode), increase weld shrinkage and

causes greater distortions

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•excessively high current: digging arc, undercut,

burn through; also a high and narrow bead &

solidification cracking

•too low current: incomplete

fusion or inadequate penetration

•excessively low current:

unstable arc

SAW operating variablesWelding voltage

•welding voltage controls arc

length

•increase in voltage produce a

flatter and wider bead

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•an increased voltage can increase pick-up of alloying elements

from an alloy flux

flatter and wider bead

•increase in voltage increase

flux consumption

•increase in voltage tend toreduce porosity

•an increased voltage may

help bridging an excessive

root gap

SAW operating variables

Welding voltage

•low voltage produce a“stiffer” arc & improves

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penetration in a deep

weld groove and resists

arc blow•excessive low voltage

produce a high narrow

bead & difficult slag

removal

SAW operating variablesWelding voltage

•excessively high voltageproduce a “hat-shaped” bead

& tendency to crack

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& tendency to crack

•excessively high voltage

increase undercut & make slagremoval difficult in groove

•excessively high voltageproduce a concave fillet weld

that is subject to cracking

SAW operating variablesTravel speed

•increase in travel speed: decrease heat input & less

filler metal applied per unit of length, less excessweld metal & weld bead becomes smaller

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SAW operating variablesTravel speed

•excessively high speed

lead to undercut, arcblow and porosity

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•excessively low speedproduce “hat-shaped” beads

danger of cracking

•excessively low speed produce rough beads andlead to slag inclusions

SAW operating variablesElectrode size

•at the same current, small electrodes have higher

current density & higher deposition rates

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SAW operating variablesElectrode extension

•increased electrode extension adds resistance in the

welding circuit I increase in deposition rate, decrease in

penetration and bead width

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•to keep a proper weld shape, when electrode extension is

increased, voltage must also be increased

•when burn-through is a problem (e.g. thin gauge), increase

electrode extension

•excessive electrode extension: it is more difficult to

maintain the electrode tip in the correct position

SAW operating variablesDepth of flux

•depth of flux layer influence the appearance of weld

•usually, depth of flux is 25-30 mm

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•if flux layer is to deep the arc is too confined, result is

a rough ropelike appearing weld

•if flux layer is to deep the gases cannot escape & thesurface of molten weld metal becomes irregularly

distorted

•if flux layer is too shallow, flashing and spattering will

occur, give a poor appearance and porous weld

SAW technological variablesTravel angle effect - Butt weld on plates

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Penetration Deep Moderate ShallowExcess weld metal Maximum Moderate Minimum

Tendency to undercut Severe Moderate Minimum

SAW technological variablesEarth position +

Direction of

travel

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•welding towards earth produces backward arc blow

•deep penetration

•convex weld profile

SAW technological variablesEarth position

Direction oftravel

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•welding away earth produces forward arc blow

•normal penetration depth

•smooth, even weld profile

Weld backing

Backing strip

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Backing weld

Copper backing

Starting/finishing the weld

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SAW variants

Twin wire SAW welding •two electrodes are feed

into the same weld pool

•wire diameter usually 1,6 to3,2 mm

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•electrodes are connected

to a single power source & a

single arc is established

•normally operate with

•offers increased depositionrate by up to 80% compared

to single wire SAW

SAW variants

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Wires can be oriented

for maximum or

minimum penetration

SAW variantsTandem arc SAW process •usually DCEP on lead

and AC on trail to reduce

arc blow•requires two separate

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power sources

•the electrodes are active

in the same puddle BUTthere are 2 separate arcs

•increased deposition

rate by up to 100%

compared with single

wire SAW

SAW variantsSAW tandem arc

with two wires

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Courtesy of ESAB AB

SAW variants

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Single pool - highest deposition rate

Twin pool - travel speed limited by undercut;

very resistant to porosity and cracks

SAW variants

Tandem arc SAW process - multiple wires

•only for welding thick

sections (>30 mm)

•not suitable for use in

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•not suitable for use in

narrow weld

preparations (root

passes)

•one 4 mm wire at 600 A,

6.8 kg/hr

•tandem two 4 mm wiresat 600 A, 13.6 kg/hr Courtesy of ESAB AB

SAW variantsStrip cladding needs a

special welding head

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SAW variantsNarrow gap welding

•for welding thick

materials

•less filler metal required

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•requires special groove

preparation and special

welding head•requires special fluxes,

otherwise problems with

slag removal

•defect removal is verydifficult

SAW variantsHot wire welding

•the hot wire is connected to power source & much

more efficient than cold wire (current is used entirelyto heat the wire!)

i d iti t

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•increase deposition rates

up to 100%

•requires additionalwelding equipment,

additional control of

variables, considerable

set-up time and closeroperator attention

SAW variants

SAW with metal powder addition

•increased deposition rates up to70%; increased welding speed

•gives smooth fusion, improvedbead appearance, reduced

i d dil i f

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penetration and dilution from parentmetal & higher impact strength

•metal powders can modifychemical composition of final welddeposit

•does not increase risk of cracking

•do not require additional arc energy

•metal powder can be added aheador directly into the weld pool

SAW variants

SAW with metal powder addition

•magnetic attachment of powder

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•SAW with metal cored wires

SAW variantsStorage tank

SAW of circular

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Courtesy of ESAB AB

Advantages of SAW• high current density, high deposition rates (up to 10 times

those for MMA), high productivity

• deep penetration allowing the use of small welding grooves

• fast travel speed, less distortion

• deslagging is easier

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• uniform bead appearance with good surface finish and good

fatigue properties

• can be easily performed mechanised, giving a higher dutycycle and low skill level required

• provide consistent quality when performed automatic or

mechanised

• Virtually assured radiographically sound welds

• arc is not visible

• little smoke/fumes are developed

Advantages

• Low weld-metal cost

• Easily automated

Disadvantages

• Restricted weldingpositions

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• Low levels of ozone

• High productivity

• No visible arc light

• Minimum cleaning

• Arc blow on DC

current

• Shrinkage defects

• Difficult penetration

control

• Limited joints

Welding Inspector

Welding Consumables

Section 14

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BS EN 499 MMA Covered Electrodes

Covered Electrode

Toughness

Yield Strength N/mm2

E 50 3 2Ni B 7 2 H10

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Toughness

Chemical composition

Flux Covering

Weld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

Welding consumables are any products that are used up in

the production of a weld

Welding consumables may be:• Covered electrodes, filler wires and electrode wires.

Welding consumables

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• Shielding or oxy-fuel gases.

• Separately supplied fluxes.

• Fusible inserts.

Welding Consumable Standards

MMA (SMAW)

• BS EN 499: Steel electrodes

• AWS A5.1 Non-alloyed steel

MIG/MAG (GMAW) TIG (GTAW)

• BS 2901: Filler wires

• BS EN 440: Wire electrodes

• AWS A5.9: Filler wires

electrodes

• AWS A5.4 Chromiumelectrodes

• AWS A5.5 Alloyed steel

electrodes

• BS EN 439: Shielding gases

SAW• BS 4165: Wire and fluxes

• BS EN 756: Wire electrodes

• BS EN 760: Fluxes

• AWS A5.17: Wires and fluxes

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Welding Consumable Gases

welding gases

• GMAW, FCAW, TIG, Oxy- Fuel

• Supplied in cylinders or storage

tanks for large quantities

• Colour coded cylinders to minimisewrong use

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wrong use

• Subject to regulations concernedhandling, quantities and positioning

of storage areas• Moisture content is limited to avoid

cold cracking

• Dew point (the temperature at whichthe vapour begins to condense)must be checked

Welding ConsumablesEach consumable is critical in respect to:

• Size, (diameter and length)

• Classification / Supplier

C di i

• Condition

• Treatments e.g. baking / drying

• Handling and storage is critical for consumable control

• Handling and storage of gases is critical for safety

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MMA Covered Electrodes

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The three main electrode covering types used in MMA welding

• Cellulosic - deep penetration/fusion

• Rutile - general purpose

• Basic - low hydrogen

MMA Welding ConsumablesWelding consumables for MMA:

• Consist of a core wire typically between 350-450mm in length

and from 2.5mm - 6mm in diameter

Th i i d ith t d d fl ti

• The wire is covered with an extruded flux coating

• The core wire is generally of a low quality rimming steel

• The weld quality is refined by the addition of alloying and

refining agents in the flux coating

• The flux coating contains many elements and compounds

that all have a variety of functions during welding

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MMA Welding ConsumablesFunction of the Electrode Covering:

• To facilitate arc ignition and give arc stability

• To generate gas for shielding the arc & molten metal from aircontamination

• To de-oxidise the weld metal and flux impurities into the slag

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To de oxidise the weld metal and flux impurities into the slag

• To form a protective slag blanket over the solidifying andcooling weld metal

• To provide alloying elements to give the required weld metalproperties

• To aid positional welding (slag design to have suitablefreezing temperature to support the molten weld metal)

• To control hydrogen contents in the weld (basic type)

1: Electrode size (diameter and length)

2: Covering condition: adherence, cracks, chips and concentricity

Covered electrode inspection

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3: Electrode designation

EN 499-E 51 3 B

Arc ignition enhancing materials (optional!)

See BS EN ISO 544 for further information

Plastic foil sealed cardboard box•rutile electrodes

•general purpose basic electrodes

Courtesy of Lincoln Electric c

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Tin can

•cellulosic electrodes

Vacuum sealed pack

•extra low hydrogen electrodes

Courtesy of Lincoln Electric

C o u r t e s y o f L i n c o l n E l e c t r i c

MMA Welding ConsumablesCellulosic electrodes:

• covering contains cellulose (organic material).

• produce a gas shield high in hydrogen raising the arcvoltage.

D i / f i h i i bl ldi

• Deep penetration / fusion characteristics enables welding

at high speed without risk of lack of fusion.

• generates high level of fumes and H2 cold cracking.

• Forms a thin slag layer with coarse weld profile.

• not require baking or drying (excessive heat will damage

electrode covering!).

• Mainly used for stove pipe welding

• hydrogen content is 80-90 ml/100 g of weld metal.4/23/2007 397 of 691

MMA Welding ConsumablesCellulosic Electrodes

Disadvantages:

• weld beads have high hydrogen

• risk of cracking (need to keep joint hot during welding to allow

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g ( p j g g

H to escape)

• not suitable for higher strength steels - cracking risk too

high (may not be allowed for Grades stronger than X70)

• not suitable for very thick sections (may not be used on

thicknesses > ~ 35mm)

• not suitable when low temperature toughness is required

(impact toughness satisfactory down to ~ -20 ° C)

Advantages:

• Deep penetration/fusion

Disadvantages:

• High in hydrogen

Cellulosic Electrodes

• Suitable for welding in all

positions

• Fast travel speeds

• Large volumes of shielding gas

• Low control

• High crack tendency

• Rough weld appearance

• High spatter contents

• Low deposition rates

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Rutile electrodes:

• covering contains TiO2 slag former and arc stabiliser.

• easy to strike arc, less spatter, excellent for positional

welding.

• stable, easy-to-use arc can operate in both DC and AC.

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• slag easy to detach, smooth profile.

• Reasonably good strength weld metal.

• Used mainly on general purpose work.

• Low pressure pipework, support brackets.

• electrodes can be dried to lower H2 content but cannot be

baked as it will destroy the coating.

• hydrogen content is 25-30 ml/100 g of weld metal.

MMA Welding ConsumablesRutile electrodes

Disadvantages:

• they cannot be made with a low hydrogen content

• cannot be used on high strength steels or thick joints -

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cracking risk too high

• they do not give good toughness at low temperatures

• these limitations mean that they are only suitable for general

engineering - low strength, thin steel

Advantages:

• Easy to use

• Low cost / control

Disadvantages:

• High in hydrogen

• High crack tendency

Rutile Electrodes

Low cost / control

• Smooth weld profiles

• Slag easily detachable

• High deposition possible

with the addition of iron

powder

High crack tendency

• Low strength

• Low toughness values

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MMA Welding ConsumablesRutile Variants

High Recovery Rutile Electrodes

Characteristics:

• coating is „bulked out‟ with iron powder

• iron powder gives the electrode „high recovery‟

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• extra weld metal from the iron powder can mean that weld

deposit from a single electrode can be as high as 180% of

the core wire weight

• give good productivity

• large weld beads with smooth profile can look very similar to

SAW welds

MMA Welding ConsumablesHigh Recovery Rutile Electrodes

Disadvantages:

• Same as standard rutile electrodes with respect to hydrogen

control

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• large weld beads produced cannot be used for all-positional

welding

• the very high recovery types usually limited to PA & PB

positions

• more moderate recovery may allow PC use

Basic covering:

• Produce convex weld profile and difficult to detach slag.

• Very suitable for for high pressure work, thick section steeland for high strength steels.

• Prior to use electrodes should be baked, typically 350°C for 2h l d i l l l d hi

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hour plus to reduce moisture to very low levels and achievelow hydrogen potential status.

• Contain calcium fluoride and calcium carbonate compounds.

• cannot be re-baked indefinitely!

• low hydrogen potential gives weld metal very goodtoughness and YS.

• have the lowest level of hydrogen (less than 5 ml/100 g ofweld metal).

MMA Welding ConsumablesBasic Electrodes

Disadvantages:

• Careful control of baking and/or issuing of electrodes isessential to maintain low hydrogen status and avoid risk ofcracking

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• Typical baking temperature 350°C for 1 to 2hours.

• Holding temperature 120 to 150°C.• Issue in heated quivers typically 70°C.

• Welders need to take more care / require greater skill.

• Weld profile usually more convex.

• Deslagging requires more effort than for other types.

Basic Electrodes

Advantages

• High toughness values

• Low hydrogen contents

Disadvantages

• High cost

• High control

Low hydrogen contents

• Low crack tendency

High control

• High welder skill

required

• Convex weld profiles

• Poor stop / start

properties

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BS EN 499 MMA Covered Electrodes

Covered Electrode

Toughness

Yield Strength N/mm2

E 50 3 2Ni B 7 2 H10

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Chemical composition

Flux CoveringWeld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

BS EN 499 MMA Covered ElectrodesElectrodes classified as follows:

• E 35 - Minimum yield strength 350 N/mm2

Tensile strength 440 - 570 N/mm

Tensile strength 470 600 N/mm2

Tensile strength 470 - 600 N/mm2

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AWS A5.1 Alloyed Electrodes

Covered Electrode

Tensile Strength (p.s.i)

60 1 3

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Welding Position

Flux Covering

AWS A5.5 Alloyed Electrodes

Covered Electrode

Tensile Strength (p.s.i)

70 1 8 M G

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Welding Position

Flux CoveringMoisture Control

Alloy Content

MMA Welding ConsumablesTYPES OF ELECTRODES

(for C, C-Mn Steels)

BS EN 499 AWS A5.1

• Cellulosic E XX X C EXX10

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• RutileE XX X R EXX12

• Rutile Heavy Coated E XX X RR EXX24

• Basic E XX X B EXX15

EXX16EXX18

Electrode efficiency

up to 180% for iron powder electrodes

Mass of weld metal deposited

Electrode Eficiency =

75-90% for usual electrodes

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Electrode Eficiency =

Mass of core wire melted

Covered electrode treatment

Cellulosic

electrodes

Use straight from the

box - No baking/drying!

If necessary, dry up to

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Rutile

electrodes

y, y p

120°C- No baking!

Vacuum

packed basic

electrodes

Use straight from the pack

within 4 hours - No

rebaking!

Covered electrode treatment

After baking maintain in

Basic electrodesBaking in oven 2 hours

at 350°C!

Limited number of

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After baking, maintain in

oven at 150°C

Use from quivers at

If not used within 4

hours, return to oven

and rebake!

Limited number of

rebakes!

TIG Consumables

Welding Consumables

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TIG Welding ConsumablesWelding consumables for TIG:

•Filler wires, Shielding gases, tungsten electrodes (non-

consumable).

•Filler wires of different materials composition and variable

diameters available in standard lengths with applicable

diameters available in standard lengths, with applicable

code stamped for identification

•Steel Filler wires of very high quality, with copper coating to

resist corrosion.

•shielding gases mainly Argon and Helium, usually of highest

purity (99.9%).

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TIG Welding Consumables

Welding rods:

•supplied in cardboard/plastic tubes

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•must be kept clean and free from oil and dust

•might require degreasing

Courtesy of Lincoln Electric

Fusible InsertsPre-placed filler material

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Before Welding After Welding

Other terms used include:

EB inserts (Electric Boat Company)

Consumable socket rings (CSR)

Fusible Inserts

Consumable inserts:

• used for root runs on pipes

• used in conjunction with TIG welding• available for carbon steel, Cr-Mo steel, austenitic stainless

steel, nickel and copper-nickel alloys

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• different shapes to suit application

Radius

Fusible Inserts

Application of consumable inserts

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Shielding gases for TIG welding

• low cost and greater availability

• heavier than air - lower flow rates than Helium

• low thermal conductivity - wide top bead profile

• low ionisation potential - easier arc starting, better arc

stability with AC, cleaning effect

• for the same arc current produce less heat than helium -reduced penetration, wider HAZ

• to obtain the same arc arc power, argon requires a higher

current - increased undercut

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Helium

• costly and lower availability than Argon

• lighter than air - requires a higher flow rate compared with

argon (2-3 times)

• higher ionisation potential - poor arc stability with AC, less

forgiving for manual welding

• for the same arc current produce more heat than argon -

increased penetration, welding of metals with high melting

point or thermal conductivity

• to obtain the same arc arc power, helium requires a lower

current - no undercut4/23/2007 424 of 691

Hydrogen

• not an inert gas - not used as a primary shielding gas

• increase the heat input - faster travel speed and increasedpenetration

• better wetting action - improved bead profile

better wetting action improved bead profile

•produce a cleaner weld bead surface

• added to argon (up to 5%) - only for austenitic stainlesssteels and nickel alloys

• flammable and explosive

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Nitrogen

• not an inert gas

• high availability - cheap

• added to argon (up to 5%) - only for back purge for duplex

stainless, austenitic stainless steels and copper alloys

• not used for mild steels (age embritlement)

• strictly prohibited in case of Ni and Ni alloys (porosity)

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MIG / MAG Consumables(Gases Covered previously)

Welding Consumables

( p y)

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MIG/MAG Welding ConsumablesWelding consumables for MIG/MAG

• Spools of Continuous electrode wires and shielding gases

• variable spool size (1-15Kg) and Wire diameter (0.6-1.6mm) supplied in random or orderly layers

• Basic Selection of different materials and their alloys as

electrode wires.

• Some Steel Electrode wires copper coating purpose is

corrosion resistance and electrical pick-up

• Gases can be pure CO2, CO2+Argon mixes and Argon+2%O2

mixes (stainless steels).

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MIG/MAG Welding Consumables

Welding wires:

•carbon and low alloy wires may be copper coated

• stainless steel wires are not coated

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•wires must be kept clean and free from oil and dust

•flux cored wires does not require baking or drying

Courtesy of Lincoln Electric Courtesy of ESAB AB

Flux Core Wire Consumables(Not in training manual)

Welding Consumables

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Flux Core Wire Consumables

Functions of metallic sheath: Function of the filling powder:

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provide form stabilityto the wire

serves as currenttransfer duringwelding

stabilise the arcadd alloy elements

produce gaseousshield

produce slag

add iron powder

Types of cored wire

Seamless

cored wire

Butt joint

cored wire

Overlapping

cored wire

• not sensitive to moisturepick-up

• can be copper coated, bettercurrent transfer

• thick sheath, good formstability, 2 roll drive feeding

possible• difficult to manufacture

• good resistance tomoisture pick-up

• can be copper coated

• thick sheath

• difficult to seal the

sheath

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cored wire cored wire cored wire

sensitive tomoisture pick-

cannot be

copper coated

thin sheatheasy to

manufacture

Core elements and their function

Aluminium - deoxidize & denitrify

Calcium - provide shielding & form slag

Carbon - increase hardness & strength

Manganese - deoxidize & increase strength and toughness

Molybdenum - increase hardness & strength

Nickel - improve hardness, strength, toughness & corrosion

resistance

Potassium - stabilize the arc & form slag

Silicon - deoxidize & form slag

Sodium - stabilize arc & form slag

Titanium - deoxidize, denitrify & form slag4/23/2007 436 of 691

SAW Consumables

Welding Consumables

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SAW ConsumablesWelding fluxes:

• are granular mineral compounds mixed according to various

formulations

• shield the molten weld pool from the atmosphere

• clean the molten weld pool

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• can modify the chemical composition of the weld metal

• prevents rapid escape of heat from welding zone

• influence the shape of the weld bead (wetting action)

• can be fused, agglomerated or mixed

• must be kept warm and dry to avoid porosity

SAW Consumables

Welding flux:

• might be fused or agglomerated

• supplied in bags

• must be kept warm and dry

• handling and stacking requires care

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• Fused fluxes are normally not hygroscopic but particles canhold surface moisture so only drying

• Agglomerated fluxes contain chemically bonded water. Similar

treatment as basic electrodes

• If flux is too fine it will pack and not feed properly. It cannot berecycled indefinitely

handling and stacking requires careCourtesy of Lincoln Electric

SAW Consumables

Fused Flux

• Flaky appearance

• Lower weld quality

• Low moisture intake

• Low dust tendency

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Fused Flux:

Baked at high temperature, glossy, hard and black in colour,

cannot add ferro-manganese, non moisture absorbent andtends to be of the acidic type

• Good re-cycling

• Very smooth weld

profile

SAW ConsumablesTYPES OF FLUX

FUSED (ACID TYPE)

• name indicates method of manufacture

• minerals are fused (melted) and granules produced byallowing to cool to a solid mass and then crushing or by

spraying the molten flux into water

• flux tends to be „glass-like‟ (high in Silica)

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g ( g )

• granules are hard and may appear shiny

• granules do not absorb moisture

• granules do not tend break down into powder when being

re-circulated

• are effectively a low hydrogen flux

• welds do not tend to give good toughness at lowtemperatures

SAW ConsumablesFused fluxes advantages:

•good chemical homogeneity

•easy removal of fines without affecting flux

composition

•normally not hygroscopic easy storage and

handling

dil l d ith t i ifi t h i

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•readily recycled without significant change in

particle size or compositionFused fluxes disadvantages:

•difficult to add deoxidizers and ferro-alloys (due to

segregation or extremely high loss)

•high temperatures needed to melt ingredients limitthe range of flux compositions

SAW ConsumablesAgglomerated Flux

• Granulated appearance

• High weld quality• Addition of alloys

• Lower consumption

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Agglomerated Flux:

Baked at a lower temperature, dull, irregularly shaped, friable,

(easily crushed) can easily add alloying elements, moistureabsorbent and tend to be of the basic type

• Easy slag removal

• Smooth weld profile

SAW Consumables

Agglomerated fluxes advantages:

• easy addition of deoxidizers and alloying elements

• usable with thicker layer of flux when welding• colour identification

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Agglomerated fluxes disadvantages:

• tendency to absorb moisture

• possible gas evolution from the molten slag leading to

porosity

• possible change in flux composition due to segregation orremoval of fine mesh particles

SAW ConsumablesTYPES OF FLUX

AGGLOMERATED (BASIC TYPE)

• name indicates method of manufacture

• basic minerals are used in powder form and are mixed with abinder to form individual granules

• granules are soft and easily crushed to powder

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• granules will absorb moisture and it is necessary to protect

the flux from moisture pick-up - usually by holding in aheated silo

• granules tend to break down into powder when being re-circulated

• are a low hydrogen flux - if correctly controlled

• welds give good toughness at low temperatures

SAW Consumables

Mixed fluxes advantages:

•several commercial fluxes may be mixed for highly

critical or proprietary welding operations

Mixed fluxes - two or more fused or bonded fluxes are

mixed in any ratio necessary to yield the desired

results

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Mixed fluxes disadvantages:

•segregation of the combined fluxes duringshipment, storage and handling

•segregation occurring in the feeding and recovery

systems during welding

•inconsistency in the combined flux from mix to mix

SAW filler material

Welding wires can be used to weld:

•carbon steels

•low alloy steels•creep resisting steels

•stainless steels

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stainless steels

•nickel-base alloys

•special alloys for surfacing applications

Welding wires can be:

•solid wires

•metal-cored wires

SAW filler material

Welding wires:

•carbon and low alloy wires are copper coated

•stainless steel wires are not coated

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•wires must be kept clean and free from oil and dust

Courtesy of Lincoln Electric Courtesy of Lincoln Electric

SAW filler material

Copper coating functions:

•to assure a good electric contact between wireand contact tip

•to assure a smooth feed of the wire through the

id t b f d ll d t t ti (d

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guide tube, feed rolls and contact tip (decrease

contact tube wear)

•to provide protection against corrosion

Welding Inspector

Non Destructive Testing

Section 15

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Non-Destructive Testing

A welding inspector should have a working knowledge of NDT

methods and their applications, advantages and

disadvantages.

Four basic NDT methods

• Radiographic inspection (RT)

• Ultrasonic inspection (UT)

• Magnetic particle inspection (MT)

• Dye penetrant inspection (PT)

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Non-Destructive TestingSurface Crack Detection

• Liquid Penetrant (PT or Dye-Penetrant)

• Magnetic Particle Inspection (MT or MPI)

Volumetric & Planar Inspection

• Ultrasonics (UT)

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• Radiography (RT)

Each technique has advantages & disadvantages with respect

• Technical Capability and Cost

Note: The choice of NDT techniques is based on considerationof these advantages and disadvantages

Radiographic Testing (RT)

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g p g ( )

Radiographic Testing

The principles of radiography

• X or Gamma radiation is imposed upon a test object

• Radiation is transmitted to varying degrees

dependant upon the density of the material through

which it is travelling

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• Thinner areas and materials of a less density show asdarker areas on the radiograph

• Thicker areas and materials of a greater density show

as lighter areas on a radiograph

• Applicable to metals,non-metals and composites

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X – Rays

Electrically generated

Gamma Rays

Generated by the decay

of unstable atoms

Radiographic TestingSource

Radiation beam Image quality indicator

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Radiographic film with latent image after exposure

Test specimen

Radiographic TestingDensity - relates to the degree of darkness

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Contrast - relates to the degree of difference

Definition - relates to the degree of sharpness

Sensitivity - relates to the overall quality of the radiograph

Densitometer

Radiographic Sensitivity

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Step / Hole type IQI Wire type IQI

Radiographic Sensitivity

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Wire Type IQI

Step/Hole Type IQI

Radiographic TechniquesSingle Wall Single Image (SWSI)

• film inside, source outside

Single Wall Single Image (SWSI) panoramic

• film outside, source inside (internal exposure)

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Double Wall Single Image (DWSI)

• film outside, source outside (external exposure)

Double Wall Double Image (DWDI)

• film outside, source outside (elliptical exposure)

Single Wall Single Image (SWSI)

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IQI‟s should be placed source side

Single Wall Single Image Panoramic

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• IQI‟s are placed on the film side

• Source inside film outside (single exposure)

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• IQI‟s are placed on the film side

• Source outside film outside (multiple exposure)

• This technique is intended for pipe diametersover 100mm

• Identification

• Unique identificationEN W10

• IQI placing

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Radiograph

ID MR11

• IQI placing

A B• Pitch marks indicatingreadable film length

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Radiograph

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• IQI‟s are placed on the source or film side

• Source outside film outside (multiple exposure)

• A minimum of two exposures

• This technique is intended for pipe diameters less than 100mm

• Identification

• Unique identification EN W10

• IQI placing

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Shot A Radiograph

ID MR12

IQI placing

1 2• Pitch marks indicating

readable film length

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Elliptical Radiograph

Radiography

PENETRATING POWER

Question:

What determines the penetrating power of an X-ray ?

•the kilo-voltage applied (between anode & cathode)

Question:

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What determines the penetrating power of a gamma ray ?

•the type of isotope (the wavelength of the gamma rays )

Radiography

GAMMA SOURCES

Isotope Typical Thickness Range

• Iridium 192 10 to 50 mm (mostly used)

• Cobalt 60 > 50 mm

Ytt bi < 10

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• Ytterbium < 10 mm

• Thulium < 10 mm

• Cesium < 10 mm

Advantages

• Permanent record

• Little surface preparation

• Defect identification

• No material type limitation

N t li t t

Disadvantages

• Expensive consumables

• Bulky equipment

• Harmful radiation

• Defect require significant

depth in relation to the

radiation beam (not good

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• Not so reliant upon operator

• Thin materials

radiation beam (not good

for planar defects)

• Slow results

• Very little indication of

depths

• Access to both sides

required

Radiograph ic Test ing

Comparison with Ultrasonic Examination

ADVANTAGES

good for non-planar defects

good for thin sections

gives permanent record

i f 2 d t i t t ti

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easier for 2nd party interpretation

can use on all material types

high productivity

direct image of imperfections

Comparison with Ultrasonic Examination

DISADVANTAGES

• health & safety hazard

• not good for thick sections

• high capital and relatively high running costs

• not good for planar defects

• X-ray sets not very portable

• requires access to both sides of weld

• frequent replacement of gamma source needed (half life)

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Ultrasonic Testing (UT)

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Ultrasonic Testing

Main Features:

• Surface and sub-surface detection

• This detection method uses high frequency sound waves,

typically above 2MHz to pass through a material

• A probe is used which contains a piezo electric crystal to

transmit and receive ultrasonic pulses and display the

signals on a cathode ray tube or digital display

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• The actual display relates to the time taken for theultrasonic pulses to travel the distance to the interface and

• An interface could be the back of a plate material or a defect

• For ultrasound to enter a material a couplant must be

introduced between the probe and specimen

Ultrasonic Testing

Digital

UT Set,

Pulse echo

signals

A scan

Display

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Compression probe checking the material Thickness

Ultrasonic Testing

defect

Back wall

echoinitial pulse

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defect

0 10 20 30 40 50

CRT DisplayCompression Probe

Material Thk

Ultrasonic Testing

UT SetA Scan

Display

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Angle Probe

Ultrasonic Testing

initial pulse

defect echo

defect

0 10 20 30 40 50

CRT Display½ Skip

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defect 0 10 20 30 40 50

initial pulse

defect echo

CRT DisplayFull Skip

Ultrasonic Testing

Advantages

Rapid results

Both surface and

sub-surface detection

Capable of measuring the

Disadvantages

Trained and skilled operator

required

Requires high operator skill

Good surface finish required

Defect identification

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Capable of measuring the

depth of defects

May be battery powered

Portable

Couplant may contaminate

No permanent record

Calibration Required

Ferritic Material (Mostly)

Ultrasonic Testing

Comparison with Radiography

ADVANTAGES

•good for planar defects

•good for thick sections

•instant results

•can use on complex joints

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can use on complex joints

•can automate

•very portable

•no safety problems (‘parallel’ working is possible)

•low capital & running costs

Ultrasonic Testing

Comparison with Radiography

DISADVANTAGES

• no permanent record (with standard equipment)

• not suitable for very thin joints <8mm

• reliant on operator interpretation

reliant on operator interpretation

• not good for sizing Porosity

• good/smooth surface profile needed

• not suitable for coarse grain materials (e.g., castings)

• Ferritic Materials (with standard equipment)

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Magnetic Particle testing (MT)

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Magnetic Particle Testing

Electro-magnet (yoke) DC or AC

Collection of ink

particles due to

leakage field

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Electro-magnet (yoke) DC or AC

Prods DC or AC

A crack like

indication

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Alternatively to contrast inks, fluorescent inks may be used

for greater sensitivity. These inks require a UV-A light source

and a darkened viewing area to inspect the component

Typical sequence of operations to inspect a weld

• Clean area to be tested

• Apply contrast paint• Apply magnetisism to the component

• Apply ferro-magnetic ink to the component during

magnatising

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• Iterpret the test area

• Post clean and de-magnatise if required

Advantages

• Simple to use

• Inexpensive

• Rapid results

• Little surface preparation

required

Disadvantages

• Surface or slight sub-surface

detection only

• Magnetic materials only

• No indication of defects

depths

Only suitable for linear

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• Possible to inspect throughthin coatings

• Only suitable for linear

defects

• Detection is required in two

directions

Comparison with Penetrant Testing

ADVANTAGES

• much quicker than PT

• instant results

• can detect near-surface imperfections (by current f low

technique)

• less surface preparation needed

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• less surface preparation needed

DISADVANTAGES

• only suitable for ferromagnetic materials

• electrical power for most techniques

• may need to de-magnetise (machine components)

Penetrant Testing (PT)

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Penetrant TestingMain features:

• Detection of surface breaking defects only.

• This test method uses the forces of capillary action

• Applicable on any material type, as long they are non porous.

• Penetrants are available in many different types:

• Water washable contrast

• Solvent removable contrast

• Water washable fluorescent

• Solvent removable fluorescent

• Post-emulsifiable fluorescent

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Penetrant Testing

Step 2. Apply penetrant

After the application, the penetrant is normally left on the

components surface for approximately 15-20 minutes (dwell

time).

The penetrant enters any defects that may be present bycapillary action.

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Penetrant Testing

Step 3. Clean off penetrant

the penetrant is removed after sufficient penetration time (dwell

time).

Care must be taken not to wash any penetrant out off any

defects present

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Penetrant Testing

Step 3. Apply developer

After the penetrant has be cleaned sufficiently, a thin layer of

developer is applied.

The developer acts as a contrast against the penetrant and

allows for reverse capillary action to take place.

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Penetrant Testing

Step 4. Inspection / development time

Inspection should take place immediately after the developer

has been applied.

any defects present will show as a bleed out during

development time.After full inspection has been carried out post cleaning is

generally required.

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Penetrant Testing

Fluorescent Penetrant Bleed out viewedunder a UV-A lightsource

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Colour contrast Penetrant

Bleed out viewed

under white light

Penetrant Testing

Advantages

• Simple to use

• Inexpensive

• Quick results

• Can be used on any non-

porous material

Disadvantages

• Surface breaking defect only

• little indication of depths• Penetrant may contaminate

component

• Surface preparation critical

• Post cleaning required

• Portability

• Low operator skill required

• Post cleaning required

• Potentially hazardouschemicals

• Can not test unlimited times

• Temperature dependant

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Penetrant Testing

Comparison with Magnetic Particle Inspection

ADVANTAGES

•easy to interpret results

•no power requirements

•relatively little training required

•can use on all materials

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DISADVANTAGES

•good surface finish needed

•relatively slow

•chemicals - health & safety issue

Welding Inspector

Weld Repairs

Section 16

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Weld RepairsWeld repairs can be divided into 2 specific areas:

• Production repairs

• In service repairs

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Weld Repairs

A weld repair can be a relatively straight forward activity, but

in many instances it is quite complex, and various

engineering disciplines may need to be involved to ensure a

successful outcome.

• Analysis of the defect types may be carried out by the

Q/C department to discover the likely reason for their

occurrence, (Material/Process or Skill related).

In general terms, a welding repair involves What!

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Weld Repairs

A weld repair may be used to improve weld profiles or

extensive metal removal:

•Repairs to fabrication defects are generally easier than

repairs to service failures because the repair procedure

may be followed

•The main problem with repairing a weld is the

maintenance of mechanical properties•During the inspection of the removed area prior to

welding the inspector must ensure that the defects have

been totally removed and the original joint profile has

been maintained as close as possible

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Weld RepairsIn the event of repair, it is required:

• Authorization and procedure for repair

• Removal of material and preparation for repair

• Monitoring of repair Weld

• Testing of repair - visual and NDT

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Weld Repairs• Cleaning the repair area, (removal of paint, grease, etc)

• A detailed assessment to find out the extremity of the defect.This may involve the use of a surface or sub surface NDE method.

• Once established the excavation site must be clearly identifiedand marked out.

• An excavation procedure may be required (method used i.e.grinding, arc-air gouging, preheat requirements etc).

• NDE should be used to locate the defect and confirm its removal.

• A welding repair procedure/method statement with theappropriate welding process, consumable, technique, controlledheat input and interpass temperatures etc will need to beapproved.

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Weld Repairs

• Use of approved welders.

• Dressing the weld and final visual.

• A NDT procedure/technique prepared and carried out to ensurethat the defect has been successfully removed and repaired.

• Any post repair heat treatment requirements.

• Final NDT procedure/technique prepared and carried out after

heat treatment requirements.

• Applying protective treatments (painting etc as required).

• (*Appropriate’ means suitable for the alloys being repaired and

may not apply in specific situations)

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Weld Repairs

• What will be the effect of welding distortion and residual

stress?

• Will heat treatment be required?

• What NDE is required and how can acceptability of the

repair be demonstrated?

• Will approval of the repair be required – if yes, how and by

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Production Weld Repairs

Before the repair can commence, a number of elements need

to be fulfilled:

If the defect is surface breaking and has occurred at the fusion

face the problem could be cracking or lack of sidewall fusion.If the defect is found to be cracking the cause may be

associated with the material or the welding procedure

If the defect is lack of sidewall fusion this can be apportioned

to the lack of skill of the welder.

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In this particular case as the defect is open to the surface, MPI

or DYE-PEN may be used to gauge the length of the defect and

U/T inspection used to gauge the depth.

Weld Repairs

The specification or procedure will govern how the defective

areas are to be removed. The method of removal may be:

•Grinding

•Chipping

•Machining

•Filing

•Oxy-Gas gouging

•Arc air gouging

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Defect Excavation

Arc -ai r goug ing

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Arc-air gouging features

• Operate ONLY on DCEP

• Special gouging copper

coated carbon electrode

• Can be used on carbonand low alloy steels,

austenitic stainless steels

and non-ferrous materials

• Requires CLEAN/DRY

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Requires CLEAN/DRY

compressed air supply

• Provides fast rate of metal removal

• Can remove complex shape defects

• After gouging, grinding of carbured layer is mandatory

• Gouging doesn‟t require a qualified welder!

Production Repairs

• are usually identified during production inspection

• evaluation of the reports is usually carried out bythe Welding Inspector, or NDT operator

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Plan View of defect

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Production Weld RepairsSide View of defect excavation

Side View of repair welding

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In Service Weld Repairs

In service repairs

• Can be of a very complex nature, as the component is very

likely to be in a different welding position and condition

than it was during production

• It may also have been in contact with toxic, or combustible

fluids hence a permit to work will need to be sought prior

to any work being carried out

• The repair welding procedure may look very different to the

original production procedure due to changes in these

elements.

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In Service Weld Repairs

Other factors to be taken into consideration:

Effect of heat on any surrounding areas of the component

i.e. electrical components, or materials that may become

damaged by the repair procedure.

This may also include difficulty in carrying out any required

pre or post welding heat treatments and a possible

restriction of access to the area to be repaired.

For large fabrications it is likely that the repair must also

take place on site and without a shut down of operations,

which may bring other elements that need to be

considered.

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Weld Repairs

• Is welding the best method of repair?

• Is the repair really like earlier repairs?

• What is the composition and weldability of the base metal?

• What strength is required from the repair?

• Can preheat be tolerated?

• Can softening or hardening of the HAZ be tolerated?

• Is PWHT necessary and practicable?

• Will the fatigue resistance of the repair be adequate?

•Will the repair resist its environment?

• Can the repair be inspected and tested?

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Weld repair related problems

• heat from welding may affect dimensional stability and/or

mechanical properties of repaired assembly

• due to heat from welding, YS goes down, danger of

collapse

• filler materials used on dissimilar welds may lead to

galvanic corrosion

• local preheat may induce residual stresses

• cost of weld metal deposited during a weld joint repair

can reach up to 10 times the original weld metal cost!

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Welding Inspector

Residual Stress & Distortion

Section 17

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Residual stressResidual stresses are undesirable because:

they lead to distortionthey affect dimensional stability of the

welded assembly

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they enhance the risk of brittle fracture

they can facilitate certain types of

corrosion

Residual StressesThe heating and subsequent cooling from welding producesexpansion and contractions which affect the weld metal andadjacent material.

If this contraction is prevented or inhibited residual stress will

develop.

The tendency to develop residual stresses increases when theheating and cooling is localised.

Residual stresses are very difficult to measure with any real

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accuracy.Residual stresses are self balancing internal forces and notstresses induced whilst applying external load

Stresses are more concentrated at the surface of thecomponent.

The removal of residual stresses is termed stress relieving.

Stresses

Normal Stress

Stress arising from a force perpendicular to the

cross sectional area

Compression

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Tension

Stresses

Shear Stress

Stress arising from forces which are parallel to, and

lie in the plane of the cross sectional area.

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Shear Stress

Stresses

Hoop Stress

Internal stress acting on the wall a pipe or cylinder

due to internal pressure.

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Hoop Stress

Residual Stresses

Longitudinal

Along the weld – longitudinal residual stresses

Across the weld – transverse residual stresses

Through the weld – short transverse residual stresses

Residual stresses occur in welds in the following directions

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Transverse

Short Transverse

Residual stress

Heating and

cooling causesexpansion and

contraction

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Residual stress

In case of a heated

bar, the resistanceof the surrounding

material to the

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expansion andcontraction leads

to formation of

residual stress

Summary

1. Residual stresses are locked in elastic strain, which is

caused by local expansion and contraction in the weld

2. Residual stresses should be removed from structures

after welding.

3. The amount of contraction is controlled by, the volume of

weld metal in the joint, the thickness, heat input, joint

design and the materials properties

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4. Offsetting may be used to finalise the position of the joint.

5. If plates or pipes are prevented from moving by tacking,

clamping or jigging etc (restraint), then the amount of

residual stresses that remain will be higher.

Summary

6. The movement caused by welding related stresses is

called distortion.

7. The directions of contractional stresses and distortion is

very complex, as is the amount and type of final distortion,

however we can say that there are three directions:

a. Longi tud ina l b. Transverse c. Short transv erse

8. A high percentage of residual stresses can be removed by

heat treatments.

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9. The peening of weld faces will only redistribute the

residual stress, and place the weld face in compression.

Types of distortion

Angular distortion

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Distortion

Angular DistortionTransverse Distortion

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Bowing Distortion Longitudinal Distortion

Distortion

Factors which affect distortion

• Material properties and condition

• Heat input

• The amount of restrain

• The amount of weld metal deposited

Control of distortion my be achieved in the following way:

Th d f diff t j i t d i

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•The used of a different joint design

•Presetting the joints to be welded – so that the metal distorts

into the required position.

•The use of a balanced welding technique

•The use of clamps, jigs and fixtures.

Distortion

• Distortion will occur in all welded joints if the material are

free to move i.e. not restrained

• Restrained materials result in low distortion but high

residual stress

• More than one type of distortion may occur at one time

• Highly restrained joints also have a higher crack tendency

than joints of a low restraint

The action of resid al stress in elded joints is to ca se

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• The action of residual stress in welded joints is to causedistortion

Factors affecting distortion

Parent material properties:

thermal expansion coefficient - the greater the value, thegreater the residual stress

yield strength - the greater the value, the greater theresidual stress

Young‟s modulus - the greater the value (increase instiffness), the greater the residual stress

thermal conductivity - the higher the value, the lower theid l t

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residual stress

transformation temperature - during phasetransformation, expansion/contraction takes place. Thelower the transformation temperature, the lower the

residual stress

Joint design:

weld metal volume

type of joint - butt vs. fillet, single vs. double side

Amount of restrain:

thickness - as thickness increase, so do the stresses

high level of restrain lead to high stresses

preheat may increase the level of stresses (pipe

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preheat may increase the level of stresses (pipewelding!)

Fit-up:misalignment may reduce stresses in some cases

root gap - increase in root gap increases shrinkage

Welding sequence:

number of passes - every pass adds to the total

contraction

heat input - the higher the heat input, the greater

the shrinkage

travel speed - the faster the welding speed, the

less the stress

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less the stressbuild-up sequence

Distortion prevention

Distortion prevention by pre-setting

a) pre-setting of fillet joint to

prevent angular distortion

b) pre-setting of butt joint to

prevent angular distortion

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prevent angular distortionc) tapered gap to prevent

closure

Distortion

Pre-set or Offsetting:

The amount of offsetting required is generally a function of

trial and error.

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Distortion prevention by pre-bending usingstrongbacks and wedges

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DistortionClamping and jigging:

The materials to be welded are prevented from moving by theclamp or jig the main advantage of using a jig is that theelements in a fabrication can be precisely located in theposition to be welded. Main disadvantage of jigging is high

restraint and high levels of residual stresses.

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Distortion preventionDistortion prevention by restraint techniques

a) use of welding jigs

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b) use of flexible

clamps

Distortion preventionDistortion prevention by restraint techniques

c) use of strongbacks

with wedges

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d) use of fully welded

strongbacks

Distortion prevention by design

Consider eliminating the welding!!

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a) by forming the plate

b) by use of rolled or extruded sections

consider weld placement

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reduce weld metal volume

and/or number of runs

Distortion preventionThe volume of weld metal in a joint will affect the amount oflocal expansion and contraction, hence the more welddeposited the higher amount of distortion

Preparation angle 60o

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use of balanced welding

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- Transverse Shrinkage

Fillet Welds 0.8mm per weld where the leg length

does not exceed 3/4 plate thickness

Butt weld 1 5 to 3mm per weld for 60° V joint

Allowances to cover shrinkage

Distortions prevention by design

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Butt weld 1.5 to 3mm per weld for 60 V joint,depending on number of runs

- Longitudinal Shrinkage

Fillet Welds 0.8mm per 3m of weld

Butt Welds 3mm per 3m of weld

Distortion prevention by fabrication techniques

tack weldinga) tack weld straight through

to end of joint

b) tack weld one end, then use

back-step technique for

tacking the rest of the joint

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tacking the rest of the jointc) tack weld the centre, then

complete the tack welding

by the back-step technique

back to back assembly

a) assemblies tacked together

before welding

b) use of wedges for

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b) use of wedges forcomponents that distort on

separation after welding

use of stiffeners

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control welding process by:

- deposit the weld metal as quickly as possible

- use the least number of runs to fill the joint

Distortion prevention by welding procedure

reduce the number of

runs required to make a

weld (e.g. angular

distortion as a function

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distortion as a functionof number of runs for a

10 mm leg length weld)

control welding techniques by use

balanced welding about the neutral axis

control welding techniques by keeping

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control welding techniques by keepingthe time between runs to a minimum

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control welding techniques by

a) Back-step weldingb) Skip welding

Back-skip welding technique

Back-step welding technique

1. 2. 3. 4. 5. 6.

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1. 2. 3. 6.4. 5.

Distortion - Best practice for fabrication corrective techniques

using tack welds to set up and maintain the joint gap

identical components welded back to back so welding can be

balanced about the neutral axis

attachment of longitudinal stiffeners to prevent longitudinal

bowing in butt welds of thin plate structures

where there is choice of welding procedure, process and

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where there is choice of welding procedure, process and

technique should aim to deposit the weld metal as quickly as

possible; MIG in preference to MMA or gas welding and

mechanised rather than manual welding

in long runs, the whole weld should not be completed in onedirection; back-step or skip welding techniques should be used

Distortion corrective techniques

Distortion - mechanical corrective techniques

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Use of press to correct bowing in T butt joint

Distortion corrective techniquesDistortion - Best practice for mechanical corrective techniques

Use packing pieces which will over correct the distortion so

that spring-back will return the component to the correct shape

Check that the component is adequately supported during

pressing to prevent buckling

Use a former (or rolling) to achieve a straight component or

produce a curvature

As unsecured packing pieces may fly out from the press the

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As unsecured packing pieces may fly out from the press, the

following safe practice must be adopted:

- bolt the packing pieces to the platen

- place a metal plate of adequate thickness to intercept the'missile'

- clear personnel from the hazard area

Distortion - thermal corrective techniques

Localised heating to

correct distortion

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Spot heating for

correcting buckling

Line heating to correct angulardistortion in a fillet weld

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Use of wedge shaped heating

to straighten plate

Wedge shaped heating to correct distortion

a) standard rolled b) buckled edge of c) box fabrication

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)steel section

) gplate

General guidelines:

•Length of wedge = two-thirds of the plate width

•Width of wedge (base) = one sixth of its length (base to apex)

•use spot heating to remove buckling in thin sheet structures

•other than in spot heating of thin panels, use a wedge-shapedheating technique

•use line heating to correct angular distortion in plate

•restrict the area of heating to avoid over-shrinking the component

•limit the temperature to 60° to 650°C (dull red heat) in steels toprevent metallurgical damage

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prevent metallurgical damage

•in wedge heating, heat from the base to the apex of the wedge,

penetrate evenly through the plate thickness and maintain an even

temperature

Welding Inspector

Heat Treatment

Section 18

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Heat Treatment

Improve mechanical properties

Change microstructure

Reduce residual stress level

Change chemical composition

Flame ovenElectric oven/electric heating blankets

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Electric oven/electric heating blankets

induction/HF heating elements

Where? LocalGlobal

Heat TreatmentsMany metals must be given heat treatment before and afterwelding.

The inspector’s function is to ensure that the treatment isgiven correctly in accordance with the specification or as per

the details supplied.Types of heat treatment available:

•Preheat

•Annealing

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g•Normalising

•Quench Hardening

•Temper

•Stress Relief

Heat TreatmentsPre-heat treatments

• are used to increase weldability, by reducing sudden

reduction of temperature, and control expansion and

contraction forces during welding

Post weld heat treatments

d t h th ti f th ld t l

• are used to change the properties of the weld metal,

controlling the formation of crystalline structures

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Post Weld -Heat Treatments

Post Hydrogen Release (according to BS EN1011-2)

Temperature: Approximately 250 C hold up to 3 hours

Cooling: Slow cool in air

Result: Relieves residual hydrogen

Procedure: Maintaining pre-heat / interpass temperature after

completion of welding for 2 to 3 hours.

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Post Weld Heat Treatments

(A) Normalised

(B) Fully Annealed(C) Water-quenched

(D) Water-quenched & tempered

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Post Weld Heat Treatments

The inspector, in general, should ensure that:

• Equipment is as specified

• Temperature control equipment is in good condition

• Procedures as specified, is being used e.g.

o Method of application

o Rate of heating and cooling

o Maximum temperature

o Soak time

o Temperature measurement (and calibration)

• DOCUMENTATION AND RECORDS4/23/2007 573 of 691

Post Weld Heat Treatment Cycle

TemperatureSoakingTemperature

and time at the

attained temperature

heating rate Cooling rate

Variables for heat treatment process must be carefully controlled

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Heating Soaking Cooling

Post Weld Heat TreatmentRemoval of Residual Stress

Strength

500Cr-Mo steel - typical

C-Mn steel - typical

• At PWHT temp. the yield

strength of steel reduced

so that it it is not strong

enough to give restraint.

• Residual stress reduced

to very low level by

straining (typ ical ly < ~

0.5% s train)

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Temperature (°C)

100 200 300 400 500 600 700

Heat Treatment

Recommendations

• Provide adequate support (low YS at high temperature!)

•Control heating rate to avoid uneven thermal expansions

• Control soak time to equalise temperatures

• Control temperature gradients - NO direct flame impingement!

• Control furnace atmosphere to reduce scalingC l li id b i l f i

• Control cooling rate to avoid brittle structure formation

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Post Weld Heat Treatment Methods

Advantages:

Easy to set up

Good portability

repeatability and

temperature uniformity

Gas furnace heat treatment

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Disadvantages:

Limited to size of parts

Advantages:

High heating rates

Ability to heat anarrow band

Disadvantages:

High equipment

HF (Induction) local heat treatment

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Large equipment,

less portable

Advantages:

Ability to vary

heat Ability to

continuously

maintain heat

Disadvantages:

Local heat treatment usingelectric heating blankets

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Disadvantages:

Elements may

burn out or arcing

during heating

Welding Inspector

Cutting Processes

Section 19

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Use of gas flame

Welding GougingBrazing Cutting

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Heating Straightening Blasting Spraying

Regulators

Oxygen regulator Fuel gas regulator

Single stage used when slight rise in deliverypressure from full to empty cylinder

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Regulatortype

Two stage

pressure from full to empty cylinder

condition can be tolerated

used when a constant delivery

pressure from full to empty

cylinder condition is required

Flashback arrestors

Flashback - recession of the flame into or back of the mixing chamber

Flashback

quenched

at the

fl hb k

barrie

Built-

Normal

Reverse

Flashback

Built-in

reverseflow

SAFETY SAFETY SAFETY

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flashback

barrier

r flow

A jet of pure oxygen reacts with iron, that has beenpreheated to its ignition point, to produce theoxide Fe3O4 by exothermic reaction.This oxide isthen blown through the material by the velocity ofthe oxygen stream

Different types of fuel gases may be used for thepre-heating flame in oxy fuel gas cutting: i.e.acetylene, hydrogen, propane. etc

By adding iron powder to the flame we are able

to cut most metals - “Iron Powder Injection”

Oxyfuel gas cutting process

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The high intensity of heat and rapid cooling willcause hardening in low alloy and medium/high Csteels they are thus pre-heated to avoid thehardening effect

Oxyfuel gas cutting equipment

The cutting torch

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Neutral cutting flame

Neutral cutting flame withoxygen cutting stream

Oxyfuel gas cutting related terms

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Oxyfuel gas cutting quality

• Good cut - sharp top edge, fine and even drag lines, littleoxide and a sharp bottom edge

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Cut too fast -pronounced break in

the drag line,irregular cut edge

Cut too slow - top edge ismelted, deep groves in thelower portion, heavy scaling,rough bottom edge

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Preheat flame too high -

top edge is melted,

irregular cut, excess of

adherent dross

Preheat flame too low -

deep groves in the lower

part of the cut face

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Irregular travel speed - uneven

space between drag lines,

irregular bottom with adherent

Nozzle is too high abovethe works - excessivemelting of the top edge,

much oxide

Mechanised oxyfuel cutting

• can use portable carriages or gantry type machines and

obtain high productivity

• accurate cutting for complicate shapes

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OFW/C advantages/disadvantages

Disadvantages:

1) High skill factor

2) Wide HAZ

4) Slow process

5) Limited range ofconsumables

3) Safety issues

Advantages:

1) No need for powersupply, portable

3) Low equipment cost

2) Versatile: preheat,brazing, surfacing, repair,straightening

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consumables4) Can cut carbon and lowalloy steels

5) Good on thin materials

6) Not suitable for reactive& refractory metals

Special oxyfuel operations

• Gouging Rivet cutting

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Special oxyfuel operations

• Thin sheet cutting Rivet washing

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Cutting ProcessesPlasma arc cutting

• Uses high velocity jet of ionised gas through a

constricted nozzle to remove the molten

• Uses a tungsten electrode and water cooled

nozzle

• High quality cutting

• High intensity and UV radiation – EYES !

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Cutting Processes

Air-arc for cutting or gouging

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Air-arc gouging features

• Operate ONLY on DCEP

• Special gouging copper

coated carbon electrode

• Can be used on carbonand low alloy steels,

austenitic stainless steels

and non-ferrous materials

• Requires CLEAN/DRY

compressed air supply

• Provides fast rate of metal removal

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• Can remove complex shape defects

• After gouging, grinding of carbured layer is mandatory

• Gouging doesn‟t require a qualified welder!

Welding InspectorArc Welding Safety

Please discussSection 20

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Safety

• Electrical safety

• Heat & Light – Visible light

– UV radiation - effects on skinand eyes

• Fumes & Explosive Gasses

• Noise levels

• Fire Hazards

• Scaffolding & Staging

• Slips trips and falls

• Slips, trips and falls

• Protection of others fromexposure

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Welding InspectorWeldability Of Steels

Section 21

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Weldability of Steels

Definition

It relates to the ability of the metal (or alloy) to be welded with

mechanical soundness by most of the common welding processes,

and the resulting welded joint retain the properties for which it

has been designed.

is a function of many inter-related factors but these may be

summarised as:

•Composition of parent material

•Joint design and size

•Process and technique

•Access

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Weldability of SteelsThe weldability of steel is mainly dependant on carbon & other alloyingelements content.

If a material has limited weldability, we need to take special measures to

ensure the maintenance of the properties required

Poor weldability normally results in the occurrence of cracking

A steel is considered to have poor weldability when:

• an acceptable joint can only be made by using very narrow range ofwelding conditions

• great precautions to avoid cracking are essential (e.g., high pre-heat etc)

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The Effect of Alloying on Steels

Elements may be added to steels to produce the propertiesrequired to make it useful for an application.

Most elements can have many effects on the properties ofsteels.

Other factors which affect material properties are:

•The temperature reached before and during welding

•Heat input

•The cooling rate after welding and or PWHT

The cooling rate after welding and or PWHT

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Steel Alloying Elements

Iron (Fe): Main steel constituent. On its own, is relatively soft, ductile, with low

strength.

Carbon (C): Major alloying element in steels, a strengthening element with

major influence on HAZ hardness. Decreases weldability.

•typically < ~ 0.25%

Manganese (Mn): Secondary only to carbon for strength, toughness and

ductility, secondary de-oxidiser and also reacts with sulphur to form

manganese sulphide.

< ~0.8% is residual from steel de-oxidation

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•up to ~1.6% (in C-Mn steels) improves strength & toughness

Silicon (Si): Residual element from steel de-oxidation.

•typically to ~0.35%

Steel Alloying Elements

Phosphorus (P): Residual element from steel-making minerals. difficult to reducebelow < ~ 0.015% brittleness

Sulphur (S): Residual element from steel-making minerals

< ~ 0.015% in modern steels

< ~ 0.003% in very clean steels

Aluminium (Al): De-oxidant and grain size control

•typically ~ 0.02 to ~ 0.05%

Chromium (Cr): For creep resistance & oxidation (scaling) resistance for elevated

temperature service. Widely used in stainless steels for corrosion resistance,

increases hardness and strength but reduces ductility.

•typically ~ 1 to 9% in low alloy steels

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Nickel (Ni): Used in stainless steels, high resistance to corrosion from acids,

increases strength and toughness

Molybdenum (Mo): Affects hardenability. Steels containing molybdenum

are less susceptible to temper brittleness than other alloy steels.Increases the high temperature tensile and creep strengths of steel.typically ~ 0.5 to 1.0%

Niobium (Nb): a grain refiner, typically~ 0.05%

Vanadium (V): a grain refiner, typically ~ 0.05%

Titanium (Ti): a grain refiner typically ~ 0 05%

Steel Al loy ing Elements

Titanium (Ti): a grain refiner, typically 0.05%

Copper (Cu): present as a residual, (typically < ~ 0.30%)

added to ‘weathering steels’ (~ 0.6%) to give better resistance to

atmospheric corrosion

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Classification of Steels

Mild steel (CE < 0.4)

• Readily weldable, preheat generally not required if low hydrogenprocesses or electrodes are used

• Preheat may be required when welding thick section material, high

restraint and with higher levels of hydrogen being generated

C-Mn, medium carbon, low alloy steels (CE 0.4 to 0.5)

• Thin sections can be welded without preheat but thicker sections willrequire low preheat levels and low hydrogen processes or electrodes

should be used

Higher carbon and alloyed steels (CE > 0.5)

• Preheat, low hydrogen processes or electrodes, post weld heating andslow cooling may be required

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Process Cracks

• Hydrogen Induced HAZ Cracking (C/Mn steels)

• Hydrogen Induced Weld Metal Cracking (HSLA steels).

• Solidification or Hot Cracking (All steels)

• Lamellar Tearing (All steels)

• Re-heat Cracking (All steels, very susceptible Cr/Mo/V steels)

I t C t lli C i W ld D ( t i l t l )

• Inter-Crystalline Corrosion or Weld Decay (stainless steels)

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CrackingWhen considering any type of cracking mechanism, threeelements must always be present:

• Stress

Residual stress is always present in a weldment, throughunbalanced local expansion and contraction

• Restraint

Restraint may be a local restriction, or through platesbeing welded to each other

• Susceptible microstructure

The microstructure may be made susceptible tocracking by the process of welding

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Cracks

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May occur:

• up to 48 hrs after completion

• In weld metal, HAZ, parentmetal.

• At weld toes

• Under weld beads

• At stress raisers.

Also know as:

Cold Cracking, happens when

the welds cool down.

HAZ cracking, normally occurs

in the HAZ.

Delayed cracking, as it takes

time for the hydrogen to

migrate. 48 Hours normally but

up to 72

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up to 72,

Under-bead cracking, normally

happens in the HAZ under aweld bead

There is a risk of hydrogen cracking when all of the 4 factors

occur together:

•Hydrogen More than 15ml/100g of weld metal•Stress More than ½ the yield stress

•Temperature Below 300oC

•Hardness Greater than 400HV Vickers

•Susceptible Microstructure (Martensite)

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Precautions for controlling hydrogen cracking

• Pre heat, removes moisture from the joint preparations, and

slows down the cooling rate

• Ensure joint preparations are clean and free fromcontamination

• The use of a low hydrogen welding process and correct arc

length

• Ensure all welding is carried out is carried out under controlledenvironmental conditions

• Ensure good fit-up as to reduced stress

• The use of a PWHT

• Avoid poor weld profiles4/23/2007 614 of 691

• Hydrogen is the smallest atom known

• Hydrogen enters the weld via the arc

• Source of hydrogen mainly from moisture pick-up onthe electrodes coating, welding fluxes or from the

consumable gas

Moisture onthe electrodeor grease on

Water vapourin the air ori th

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or grease onthe wirein the

shielding gas

Oxide or grease on

the plate

Hydrogen absorbed

in a long, or

unstable arc

Hydrogen introduced in

weld from consumable,

oils, or paint on plate

Cellulosic electrodes

produce hydrogen as a

shielding gas

Hydrogen

Hydrogen Induced Cold Crack ing

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Martensite forms from γ H2 diffuses to γ in HAZ

Susceptible Microstructure:

Hard brittle structure – MARTENSITE Promoted by:

A) High Carbon Content, Carbon Equivalent (CE)

CEV = %C + Mn + Cr+Mo+V + Ni+Cu

6 5 15B) high alloy content

C) fast cooling rate: Inadequate Pre-Heating

Cold MaterialThick Material

L H t I t

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Heat input (Kj/mm) = Amps x Volts x arc time

Run out length x 103 (1000)

Low Heat Input.

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•HSLA or Micro-Alloyed Steels are high strength steels

(800MPa/N/mm2) that derive their high strength from small

percentage alloying (over-alloyed Weld metal to match the

strength of parent metal)

•Typically the level of alloying is in the elements such asvanadium molybdenum and titanium, nickel and chromium

Strength. are used. It would be impossible to match this micro

alloying in the electrode due to the effect of losses across an

electric arc (Ti burn in the arc)

•It is however important to match the strength of the weld to

the strength of the plate, Mn 1.6 Cr Ni Mo

HICC in HSLA steels

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Hydrogen Scales

List of hydrogen scales from BS EN 1011:part 2.

Hydrogen content related to 100 grams of weld metal

deposited.

• Scale A High: >15 ml

• Scale B Medium: 10 ml - 15 ml

• Scale C Low: 5 ml - 10 ml

• Scale D Very low: 3 ml - 5 ml

• Scale E Ultra-low: < 3 ml

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Potential Hydrogen Level Processes

list of welding processes in order of potential lowest hydrogen

content with regards to 100g of deposited weld metal.

•TIG < 3 ml

•MIG < 5 ml

•ESW < 5 ml

•MMA (Basic Electrodes) < 5 ml

•SAW < 10ml

•FCAW < 15 ml

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Weldability

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Usually Occurs in Weld Centerline

Solidification CrackingAlso referred as

Hot Cracking: Occurring at high temperatures while the weld is hot

Centerline cracking: cracks appear down the centre line of the bead.

Crater cracking: Small cracks in weld centers are solidification cracks

Crack type: Solidification cracking

Location: Weld centreline (longitudinal)

Steel types: High sulphur & phosphor concentration in steels.

Susceptible Microstructure: Columnar grains In direction

of solidification

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Factors for solidification cracking

• Columnar grain growth with impurities in weld metal (sulphur,

phosphor and carbon)

• The amount of stress/restraint

• Joint design high depth to width ratios

Liquid iron sulphides are formed around solidifying grains.

High contractional strains are present

High dilution processes are being used.

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There is a high carbon content in the weld metal

• Most commonly occurring in sub-arc welded joints

• Sulphur in the parent material may dilute in the weld

metal to form iron sulphides (low strength, low melting

point compounds)

• During weld metal solidification, columnar crystals pushstill liquid iron sulphides in front to the last place of

solidification, weld centerline.

• The bonding between the grains which are themselves

under great stress and may now be very poor to maintain

cohesion and a crack will result, weld centerline.

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Avoidance

Deep, narrower weld bead

On solidification thebonding between the grains

may now be very poor to

Shallow, wider weld bead

On solidification thebonding between the

grains may be adequate to

HAZ HAZ

Intergranular liquid filmColumnargrains Columnar

grains

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may now be very poor to

maintain cohesion and a

crack may result

maintain cohesion and a

crack is unlikely to occur

Precautions for controlling solidification cracking

• The use of high manganese and low carbon content fillers

• Minimise the amount of stress / restraint acting on the jointduring welding

• The use of high quality parent materials, low levels of

impurities (Phosphor & sulphur)

• Clean joint preparations contaminants (oil, grease, paints and

any other sulphur containing product)

y p g p )

• Joint design selection depth to width ratios

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Solidification cracking in Austenitic Stainless Steel

• particularly prone to solidification cracking

• large grain size gives rise to a reduction in grain boundary area with

high concentration of impurities

• Austenitic structure very intolerant to contaminants (sulphur,

phosphorous and other impurities).

• High coefficient of thermal expansion /Low coefficient of thermalconductivity, with high resultant residual stress

• same precautions against cracking as for plain carbon steels with extra

emphasis on thorough cleaning and high dilution controls.

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Cracks

Lamellar Tearing

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Lamellar Tearing

Factors for lamellar tearing to occur

Cracks only occur in the rolled plate !

Close to or just outside the HAZ !

Cracks lay parallel to the plate surface and the fusion boundaryof the weld and has a stepped aspect.

• Low quality parent materials, high levels of impurities

• Joint design, direction of stress

• The amount of stress acting across the joint during welding

The amount of stress acting across the joint during welding

• Note: very susceptible joints may form lamellar tearing under

very low levels of stress

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Lamellar Tearing

Susceptible joint types combined with susceptible rolled plateused to make a joint.

High stresses act in the through thickness direction of the plate

(know as the short transverse direction).

T, K & Y joints normally end up with a tensile residual stress

component in the through thickness direction.

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Tee fillet weld Tee butt weld(double-bevel)

Corner butt weld(single-bevel)

Lamellar Tearing

Critical area

Critical

Critical area

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Lamellar Tearing

Modifying a corner joint to avoid lamellar tearing

Susceptible Non-Susceptible

Prior welding both An open corner joint

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Prior welding bothplates may be groovedto avoid lamellar tearing

An open corner jointmay be selected toavoid lamellar tearing

Lamellar Tearing

Precautions for controlling lamellar tearing

• The use of high quality parent materials, low levels of

impurities

• The use of buttering runs

• A gap can be left between the horizontal and vertical

members enabling the contraction movement to take

• Joint design selection

Minimise the amount of stress / restraint acting on the

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• Minimise the amount of stress / restraint acting on the

joint during welding

• Hydrogen precautions

Lamellar TearingCrack type: Lamellar tearing

Location: Below weld HAZ

Steel types: High sulphur & phosphorous steels

Microstructure: Lamination & Segregation

Occurs when:

High contractional strains are through the short

transverse direction. There is a high sulfur content inthe base metal.

Th i l th h thi k d tilit i th b

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There is low through thickness ductility in the base

metal.

There is high restraint on the work

Short Tensile (Through Thickness) Test

The short tensile test or through thickness test is a

test to determine a materials susceptibility to

lamellar tearing

Friction Welded Caps

Short Tensile Specimen

ThroughThickness

Ductility

Sample of Parent Material

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The results are given as a STRA value

Short Transverse Reduction in Area

Restraint

Lamellar Tearing

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High contractional

strains

Lamellar tear

Welding Inspector

Practical Visual Inspection

Section 22

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Leg Length Gauge

G.A.L.

S.T.D.

G.A.L.

S.T.D.

Fillet Weld Gauges

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Throat Thickness Gauge

S i n g l e P u r p

o s e W e l d i n g G a u g e

Root gapdimension

Internal

alignment

HI-LO Welding Gauge

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H I - L O

Plate / Pipe Inspection

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Remember in the CSWIP 3.1 Welding Inspectors

examination your are required to conduct a practical

examination of a plate test weld, complete a thumb

print sketch and a final report on your findings

Time allowed 1 hour and 15 minutes

The code is provided

Plate Inspection Examination

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1) Use a pencil for the arrow lines, but make all

written comments and measurements in ink

3) Do not forget to compare and sentence your

report

2) Report everything that you can observe

4) Do not forget to date & sign your report

5) M k b ti h

Plate Inspection Points

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5) Make any observations, such as

recommendations for further investigation for

crack-like imperfections.

After you have observed an imperfection and

determined its type, you must be able to take

measurements and complete the thumb print report

sketchThe first thumb print report sketch should be in the

form of a repair map of the weld. (i.e. All

observations are Identified Sized and Located)

The thumb print report sketch used in CSWIP exam

will look like the following example

Plate Thumb Print Report

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will look like the following example.

After you have completed your thumb print report

sketch of your test plate the next step is to complete

your final report again the report must be completed in

ink (no pencil).

The report must be completed to your thumb print

sketch, do not leave any boxes empty, every box must

be completed or dashed out. You must also make any

comments you feel are necessary regarding anydefects observed.

Plate Inspection Final Report

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The report form used in CSWIP will look like the

following example.

Remember in the CSWIP 3.1 Welding Inspectors

examination your are required to conduct a

practical examination of a pipe test weld, complete

a thumb print sketch and a final report on your

findings

Time allowed 1 hour and 45 minutes

The code is nominated e.g API 1104

Pipe Inspection

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Welding Inspector

Application & Control of Pre heat

Section 23

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Welding TemperaturesDefinitions

Preheat temperature

• is the temperature of the workpiece in the weld zone immediately before

any welding operation (including tack welding!)

• normally expressed as a minimum Interpass temperature

– is the temperature in a multi-run weld and adjacent parent metal

immediately prior to the application of the next run

– normally expressed as a maximum

Minimum interpass temperature = Preheat temperature

Pre heat maintenance temperature = the minimum temperature in the

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Pre heat maintenance temperature the minimum temperature in the

weld zone which shall be maintained if welding is interrupted and shall be

monitored during the interruption.

Pre-heat Application

Furnace - Heating entire component - best

Electrical elements -Controllable; Portable; Site use; Clean; Component

cannot be moved.

Gas burners - direct flame impingement; Possible local overheating; Less

controllable;Portable; Manual operation possible; Component

can be moved.

Radiant gas heaters - capable of automatic control; No flameimpingement; No contact with component; Portable.

Induction heating controllable; Rapid heating (mins not hours); Large

Induction heating - controllable; Rapid heating (mins not hours); Large

power supply; Expensive equipment

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Measuring pre heat in Welding

Parameters to be measured:

welding current

arc voltage

The purposesof measuring

Demonstration of

conformance tospecified requirements

preheat/interpass

temperature

Welding

processcontrol

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travel speed

shielding gas flow rate

temperature

force/pressure

humidity

Pre-heat Application

Application Of Preheat

• Heat either side of joint

• Measure temp 2 mins after heat removal

• Always best to heat complete component rather than local if

possible to avoid distortion

• Preheat always higher for fillet than butt welds due to

different combined thicknesses and chill effect factors.

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Pre-Heat Application

Manual Gas OperationElectrical Heated

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Elements

Welding Temperatures

Point of Measurement

BS EN ISO 13916

t < 50 mm

A = 4 x t but max. 50 mm

the temperature shall be

measured on the surfaceof the workpiece facing the

welder

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Welding Temperatures

Point of Measurement

BS EN ISO 13916

t > 50mm

A = 75mm minimum

the temperature shall be

measured on the face

opposite to that beingheated

allow 2 min per every 25

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allow 2 min per every 25

mm of parent metal

thickness for temperatureequalisation

Combined Thickness

The Chilling Effect of the Joint

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Combined Thickness

The Chilling Effect of the Joint

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Combined Thickness

Combined chilling effect of joint type and

thickness.

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The Chill Effect of the Material

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Heating Temperature Control

• TEMPILSTICKS - crayons, melt at set temps. Will not measure

max temp.

• Pyrometers - contact or remote, measure actual temp.

• Thermocouples - contact or attached, very accurate, measure

actual temp.

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Temperature Test EquipmentTemperature sensitive

materials:

•crayons, paints and

pills•cheap

•convenient, easy to

•doesn‟t measure the

actual temperature!

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Temperature Test Equipment

Contact thermometer

•Accurate

•Easy to use

•Gives the actual temperature

•Requires calibration

•suitable for moderatetemperatures

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Thermocouple

• based on measuring the thermoelectric potential difference

between a hot junction (on weld) and a cold junction

• accurate method

• measures over a wide range of temperatures

• gives the actual temperature

• need calibration

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Thermistors

• temperature-sensitive resistors

whose resistance varies inversely

with temperature

• used when high sensitivity is

required

• gives the actual temperature

• need calibration

• can be used up to 999°C

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Temperature test equipmentDevices for contactless measurement

• IR radiation and optical

pyrometer

• measure the radiant energyemitted by the hot body

• contactless method, can be

used for remote measurements

• very complex

• for measuring high

temperatures

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Welding Inspector

Calibration

Section 24

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Calibration, validation and monitoringDefinitions:

Measurement = set of operations for determining a value of a

quantity

Repeatability = closeness between successive measuring

results of the same instrument carried out under the same

conditions

Accuracy class = class of measuring instruments that are

intended to keep the errors within specified limits

Calibration = checking the errors in a meter or measuring

device

Validation = checking the control knobs and switches provide

the same level of accuracy when returned to a pre-determined

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Monitoring = checking the welding parameters (and otheritems) are in accordance with the procedure or specification

Calibration and validation

Frequency - When it is required?

once a year unless otherwise specified

whenever there are indications that theinstrument does not register properly

whenever the equipment has been

damaged, misused or subject to severe

stress

whenever the equipment has been rebuild

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or repaired

See BS EN ISO 17662 for details!

Welding parameter calibration/validation

Which parameters need calibration/validation?

depends on the welding process

How accurate?

depends on the application

welding current - ±2,5%arc voltage - ±5%

wire feed speed - ±2,5%

gas flow rate - ±20% (±25% for backing gas flow rate)

temperature (thermocouple) - ±5%

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see BS EN ISO 17662 and BS 7570 for details

PAMS (Portable Arc Monitor System)

What does a PAMS measure?

Welding

current (Hall

effectdevice)

Arc voltage

(connection

leads)Temperature

Wire feed

(tachometer)

Gas flow

(heating

elementsensor)

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Temperature

(thermocouple)(tachometer)

PAMS (Portable Arc Monitor System)

The purposes of

a PAMS

For calibratingand validating

the welding

equipment

For measuringand recording

the welding

parameters

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Use of PAMS

Wire feed speedmonitoring

Incorporated pair of

rolls connected to a

tachogenerator

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Use of PAMS

Shielding gas flowrate monitoring

Heating element

sensor

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Summary• a welding power source can only be calibrated if it has

meters fitted

• the inspector should check for calibration stickers, datesetc.

• a welding power source without meters can only bevalidated that the control knobs provide repeatability

• the main role is to carryout “in process monitoring” toensure that the welding requirements are met during

ensure that the welding requirements are met duringproduction

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Welding Inspector

Macro/Micro Examination

Section 25

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Macro Preparat ion

Purpose

To examine the weld cross-section to give assurance that: -

• The weld has been made in accordance with the WPS

• The weld is free from defects

Specimen Preparation

• Full thickness slice taken from the weld (typical ly ~10mm thick)

• Width of slice sufficient to show all the weld and HAZ on both sides

plus some unaffected base material

• One face ground to a progressively fine finish (grit s izes 120 to ~ 400)

• Prepared face heavily etched to show all weld runs & all HAZ

• Prepared face examined at up to x10 (& usually photographed for records)

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• Prepared face may also be used for a hardness survey

Micro Preparat ion

PurposeTo examine a particular region of the weld or HAZ in order to:-

• To examine the microstructure

• Identify the nature of a crack or other imperfection

Specimen Preparation• A small piece is cut from the region of interest

(typical ly up to ~ 20mm x 20mm)

• The piece is mounted in plastic mould and the surface of interest

prepared by progressive grinding (to grit size 600 or 800)

• Surface polished on diamond impregnated cloths to a mirror finish

• Prepared face may be examined in as-polished condition & then lightly

etched

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• Prepared face examined under the microscope at up to ~ x 600

Macro / Micro ExaminationWill Reveal:

• Weld soundness

• Distribution of inclusions

• Number of weld passes

• Metallurgical structure of weld, fusion zone and HAZ

• Location and depth of penetration of weld

• Fillet weld leg and throat dimensions

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• Visual examination fordefects

• Cut transverse from the

• Ground & polished P400grit paper

• Acid etch using 5-10%

nitric acid solution

• Wash and dry

• Visual evaluation under 5x

magnification

• Visual examination for

defects & grain structure

• Cut transverse from a

• Ground & polished P1200grit paper, 1µm paste

• Acid etch using 1-5%

nitric acid solution

• Wash and dry

• Visual evaluation under

100-1000x magnification

Macro Micro

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• Report on results • Report on results

Metallographic Examination

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