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CSWIP 3.1 Welding Inspection

TWI Training & ExaminationTWI Training & ExaminationServicesServices

NonNon--Destructive TestingDestructive Testing

Course Reference WIS 5Course Reference WIS 5

Course notes section reference 15Course notes section reference 15

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Non-Destructive Testing

A welding inspector should have a working knowledge of NDTmethods and their applications, advantages and disadvantages.

Four basic NDT methodsFour basic NDT methods Magnetic particle inspection (MT)

Dye penetrant inspection (PT)

Radiographic inspection (RT)

Ultrasonic inspection (UT)

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Non-Destructive Testing

Surface Crack DetectionSurface Crack Detection

Liquid Penetrant (PT or Dye-Penetrant)

Magnetic Particle Inspection (MT or MPI)

Volumetric InspectionVolumetric Inspection

Ultrasonics (UT)

Radiography (RT)

Each technique has advantages & disadvantages with respectEach technique has advantages & disadvantages with respect

to:to:

Technical Capability and CostTechnical Capability and Cost

Note:Note: The choice of NDT techniques is based on consideration ofThe choice of NDT techniques is based on consideration of

these advantages and disadvantagesthese advantages and disadvantages

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Penetrant Testing (PT)Penetrant Testing (PT)

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Penetrant Testing

Main features:Main 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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Step 1. PreStep 1. Pre--CleaningCleaning

Ensure surface is very Clean normally with the use of a solvent

Penetrant Testing

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Step 2. ApplyStep 2. Apply penetrantpenetrant

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 by capillaryaction.

Penetrant Testing

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Step 3. Clean offStep 3. Clean off penetrantpenetrant

the penetrant is removed after sufficient penetration time (dwell

time).Care must be taken not to wash any penetrant out off any defectspresent

Penetrant Testing

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Step 3. Apply developerStep 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 allowsfor reverse capillary action to take place.

Penetrant Testing

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Step 4. Inspection / development timeStep 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 developmenttime.After full inspection has been carried out post cleaning is generallyrequired.

Penetrant Testing

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ColourColour contrastcontrast PenetrantPenetrant

FluorescentFluorescent PenetrantPenetrant Bleed out viewedBleed out viewedunder a UVunder a UV--A lightA light

sourcesource

Bleed out viewedBleed out viewedunder white lightunder white light

Penetrant Testing

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Penetrant Testing

AdvantagesAdvantages

Simple to use

Inexpensive

Quick results

Can be used on any non-

porous material Portability

Low operator skill required

DisadvantagesDisadvantages

Surface breaking defect only

little indication of depths

Penetrant may contaminatecomponent

Surface preparation critical

Post cleaning required Potentially hazardous

chemicals

Can not test unlimited times

Temperature dependant

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Penetrant Testing

Comparison with Magnetic Particle InspectionComparison with Magnetic Particle Inspection

ADVANTAGESADVANTAGES

easy to interpret results

no power requirements

relatively little training required

can use on all materials

DISADVANTAGESDISADVANTAGES

good surface finish needed

relatively slow

chemicals - health & safety issue

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Any QuestionsAny Questions

Penetrant Testing

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Magnetic Particle testing (MT)Magnetic Particle testing (MT)

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Magnetic Particle Testing

Main features:Main features:

Surface and slight sub-surface detection

Relies on magnetization of component being tested

Only Ferro-magnetic materials can be tested

A magnetic field is introduced into a specimen being tested

Methods of applying a magnetic field, yoke, permanent magnet,

prods and flexible cables. Fine particles of iron powder are applied to the test area

Any defect which interrupts the magnetic field, will create aleakage field, which attracts the particles

Any defect will show up as either a dark indication or in thecase of fluorescent particles under UV-A light a green/yellowindication

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A crack likeA crack like

indicationindication


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Alternatively to contrast inks, fluorescent inks may be used forAlternatively to contrast inks, fluorescent inks may be used for

greater sensitivity. These inks require a UVgreater sensitivity. These inks require a UV--A light source and aA light source and a

darkened viewing area to inspect the componentdarkened viewing area to inspect the component


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Typical sequence of operations to inspect a weldTypical 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

Iterpret the test area

Post clean and de-magnatise if required


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Simple to use

Inexpensive

Rapid results

Little surface preparation

required

Possible to inspect throughthin coatings


Surface or slight sub-surfacedetection only

Magnetic materials only

No indication of defects depths

Only suitable for linear defects Detection is required in two

directions


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Comparison with Penetrant TestingComparison with Penetrant Testing


much quicker than PT instant results

can detect near-surface imperfections (by current flow technique)

less surface preparation needed


only suitable for ferromagnetic materials

electrical power for most techniques

may need to de-magnetise (machine components)

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Ultrasonic Testing (UT)Ultrasonic Testing (UT)

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Main Features:Main Features:

Surface and subSurface and sub--surface detectionsurface detection

This detection method uses high frequency sound waves,This detection method uses high frequency sound waves,typically above 2MHz to pass through a materialtypically above 2MHz to pass through a material

A probe is used which contains aA probe is used which contains a piezopiezo electric crystal toelectric crystal to

transmit and receive ultrasonic pulses and display thetransmit and receive ultrasonic pulses and display the

signals on a cathode ray tube or digital displaysignals on a cathode ray tube or digital display The actual display relates to the time taken for theThe actual display relates to the time taken for the

ultrasonic pulses to travel the distance to the interface andultrasonic pulses to travel the distance to the interface and

backback

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

For ultrasound to enter a material a couplant must beFor ultrasound to enter a material a couplant must be

introduced between the probe and specimenintroduced between the probe and specimen

Ultrasonic Testing

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DigitalDigital

UT Set,UT Set,Pulse echoPulse echo

signalssignals

A scanA scanDisplayDisplay

Compression probeCompression probe checking the materialchecking the material ThicknessThickness

Ultrasonic Testing

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defectdefect

00 1010 2020 3030 4040 5050

defectdefect

echoechoBack wallBack wall

echoecho

CRT DisplayCRT DisplayCompression ProbeCompression Probe

MaterialMaterial ThkThk

initial pulseinitial pulse

Ultrasonic Testing

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Angle ProbeAngle Probe

UT SetUT SetA ScanA Scan

DisplayDisplay

Ultrasonic Testing

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initial pulse

defect echo

defectdefect

defect

0 10 20 30 40 50

CRT Display

0 10 20 30 40 50

initial pulse

defect echo

CRT Display

Skip

Full Skip

Ultrasonic Testing

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Rapid results

Both surface and

sub-surface detection

Safe

Capable of measuring thedepth of defects

May be battery powered

Portable


Trained and skilled operatorrequired

Requires high operator skill

Good surface finish required

Defect identification

Couplant may contaminate

No permanent record

Calibration Required

Ferritic Material (Mostly)

Ultrasonic Testing

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Ultrasonic Testing

Comparison with RadiographyComparison with Radiography


good for planar defects

good for thick sections

instant results

can use on complex joints

can automate

very portable

no safety problems (parallel working is possible)

low capital & running costs

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Ultrasonic Testing

Comparison with Radiography


no permanent record (with standard equipment) not suitable for very thin joints

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Ultrasonic Testing

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Radiographic Testing (RT)Radiographic Testing (RT)

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The principles of radiographyThe principles of radiography

X or Gamma radiation is imposed upon a test object

Radiation is transmitted to varying degrees dependant upon thedensity of the material through which it is travelling

Thinner areas and materials of a less density show as darkerareas on the radiograph

Thicker areas and materials of a greater density show as lighterareas on a radiograph

Applicable to metals,non-metals and composites

Radiographic Testing

R di hi T i

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X Rays

Electrically generated

Gamma Rays

Generated by the decay ofunstable atoms


R di hi T ti

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SourceSource

Radiation beamRadiation beam Image quality indicatorImage quality indicator

10fe16

10fe16

Test specimenTest specimenRadiographic filmRadiographic film


R di hi T ti

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SourceSource

Radiation beamRadiation beam Image quality indicatorImage quality indicator

Radiographic film with latent image after exposureRadiographic film with latent image after exposure

10fe16

10fe16

Test specimenTest specimen

10fe16

10fe16


R di hi T ti

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DensityDensity -- relates to the degree of darknessrelates to the degree of darkness

ContrastContrast -- relates to the degree of differencerelates to the degree of difference

DefinitionDefinition -- relates to the degree of sharpnessrelates to the degree of sharpness

SensitivitySensitivity -- relates to the overall quality of the radiographrelates to the overall quality of the radiograph

Densitometer

Radiographic Sensitivity

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7FE127FE12

Step / Hole type IQIStep / Hole type IQI Wire type IQIWire type IQI



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Wire Type IQIWire Type IQI

Step/Hole Type IQIStep/Hole Type IQI


Radiographic Techniques

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Single Wall Single Image (SWSI)

film inside, source outside

Single Wall Single Image (SWSI) panoramic

film outside, source inside (internal exposure)

Double Wall Single Image (DWSI)

film outside, source outside (external exposure)

Double Wall Double Image (DWDI)

film outside, source outside (elliptical exposure)

Radiographic Techniques


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IQIIQIss should be placed source sideshould be placed source side

FilmFilm

FilmFilm


Single Wall Single Image Panoramic

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IQIIQIss are placed on the film sideare placed on the film side

Source inside film outside (single exposure)Source inside film outside (single exposure)

FilmFilm

Single Wall Single Image Panoramic


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IQIIQIss are placed on the film sideare placed on the film side

Source outside film outside (multiple exposure)Source outside film outside (multiple exposure)

This technique is intended for pipe diameters over 100mmThis technique is intended for pipe diameters over 100mm

FilmFilm



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RadiographRadiograph

IdentificationIdentification

IDIDMR11MR11

Unique identificationUnique identificationEN W10EN W10

IQI placingIQI placing

AA BB Pitch marks indicatingPitch marks indicatingreadable film lengthreadable film length



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RadiographRadiograph



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FilmFilm IQIIQIss are placed on the source or film sideare placed on the source or film side

Source outside film outside (multiple exposure)Source outside film outside (multiple exposure)

A minimum of two exposuresA minimum of two exposures

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



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Shot A RadiographShot A Radiograph

IdentificationIdentification

IDMR12

Unique identificationUnique identification EN W10

IQI placingIQI placing

1 2 Pitch marks indicatingPitch marks indicating

readable film lengthreadable film length

4 3



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Elliptical RadiographElliptical Radiograph

11 22

44 33


Radiography

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Radiography

PENETRATING POWERPENETRATING POWER

Question:Question:

What determines the penetrating power of an XWhat determines the penetrating power of an X--ray ?ray ?

the kilothe kilo--voltage appliedvoltage applied (between anode & cathode)(between anode & cathode)

Question:Question:

What determines the penetrating power ofWhat determines the penetrating power of a gamma ray ?a gamma ray ?

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

Radiography

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Radiography

GAMMA SOURCESGAMMA SOURCES

IsotopeIsotope Typical Thickness RangeTypical Thickness Range

Iridium 192Iridium 192 10 to 50 mm10 to 50 mm (mostly used)(mostly used)

Cobalt 60Cobalt 60 > 50 mm> 50 mm

YtterbiumYtterbium < 10 mm< 10 mm

ThuliumThulium < 10 mm< 10 mm

CaesiumCaesium < 10 mm< 10 mm


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Permanent record

Little surface preparation

Defect identification

No material type limitation

Not so reliant upon operatorskill

Thin materials


Expensive consumables

Bulky equipment

Harmful radiation

Defect require significant

depth in relation to theradiation beam (not good forplanar defects)

Slow results

Very little indication of depths

Access to both sides required

g p g


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Comparison with Ultrasonic ExaminationComparison with Ultrasonic Examination


good for non-planar defects

good for thin sections

gives permanent record

easier for 2nd party interpretation

can use on all material types

high productivity

direct image of imperfections


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g p g

Comparison with Ultrasonic Examination


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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Questions

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QU 1.QU 1. Name four NDT methods

QU 2.QU 2. State the two radiation types used in industrial radiographyand state advantages of each.

QU 3.QU 3. Give the advantages and disadvantages of radiography andconventional ultrasonic inspection.

QU 5QU 5 State the main limitations of dye penetrant inspection.

QU 4.QU 4. Give the main disadvantages of magnetic particleinspection and give at least three methods to magnetise acomponent.

NonNon--Destructive TestingDestructive Testing

15-wis5 ndt 2006

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