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NON-DESTRUCTIVE TESTING IN

THE OFFSHORE INDUSTRY

Lecture 12

30 May 2015

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1.Introduction in Nondestructive testing.

2.Discontinuities , origin and classification3.Visual testing.

4.Liquid penetrant inspection method.

5.Process control and interpretation of liquid penetrant inspection

6.Ultrasonic inspection method

7.Ultrasonic inspection equipments and materials.8.Ultrasonic inspections process control and safety.

9.Magnetic particle testing theory10.Magnetic particle inspection applications and interpretations

11.Eddy current inspection method.12.Application on eddy current inspection

13.Acoustic emission testing.

14.Thermal infrared testing.

Topic

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10. Magnetic particle inspection

applications and interpretations

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EQUIPMENT AND ACCESSORIES

Stationary Units - A stationary unit is referred to as a wet

horizontal unit and usually has capabilities for producinglongitudinal and circular fields. Some units will also be capable of

demagnetizing the parts, although this is usually accomplished

with a separate demagnetizer. Figure below illustrates a typical

wet horizontal stationary unit.The units have head and tail

stocks (similar to a lathe) with

electrical contact that the part

can be clamped between.

A circular magnetic field is

produced with direct magnetization.

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Most units also have a movable coil that can be movedinto place so the indirect magnetization can be used toproduce a longitudinal magnetic field. Most coils have fiveturns and can be obtained in a variety of sizes.

The wet magnetic particle solution is collected and held in

a tank. A pump and hose system is used to apply theparticle solution to the components being inspected. Someof the systems offer a variety of options in electrical currentused for magnetizing the component (AC, half wave DC, orfull wave DC). In some units, a demagnetization feature is

built in, which uses the coil and decaying AC.

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Portable Equipment

Permanent Magnets

Permanent magnets can be used for magnetic particle inspectionas the source of magnetism (bar magnets or horseshoe magnets).

The use of industrial magnets is not popular because they arevery strong (they require significant strength to remove them fromthe surface, about 250 N for some magnets) and thus they aredifficult and sometimes dangerous to handle.

However, permanent magnets are sometimes used by divers forinspection in underwater environments or other areas, such asexplosive environments, where electromagnets cannot be used.Permanent magnets can also be made small enough to fit intotight areas where electromagnets might not fit.

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Electromagnetic Yokes

An electromagnetic yoke is a very common piece of equipment that isused to establish a magnetic field. A switch is included in the electricalcircuit so that the current and, therefore, the magnetic field can beturned on and off. They can be powered with AC from a wall socket or

by DC from a battery pack. This type of magnet generates a very strongmagnetic field in a local area where the poles of the magnet touch thepart being inspected.

Permanent magnets

Producing a Longitudinal Field

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Prods

Prods are handheld electrodes that are pressedagainst the surface of the component being

inspected to make contact for passing electricalcurrent (AC or DC) through the metal. Prods aretypically made from copper and have an insulatedhandle to help protect the operator. One of the prods

has a trigger switch so that the current can bequickly and easily turned on and off. Sometimes thetwo prods are connected by any insulator, as shownin the image, to facilitate one hand operation. This isreferred to as a dual prod and is commonly used forweld inspections.

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Portable Coils and Conductive Cables

Coils and conductive cables are used to establish alongitudinal magnetic field within a component. When a

preformed coil is used, the component is placed against

the inside surface on the coil. Coils typically have three

or five turns of a copper cable within the molded frame.A foot switch is often used to energize the coil.

Producing a Longitudinal Field

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Portable Power Supplies

Portable power supplies are used to provide the necessary electricity to the

prods, coils or cables.Power supplies are commercially available in a variety of sizes. Small power

supplies generally provide up to 1,500A of half-wave DC or AC. They are small

and light enough to be carried and operate on either 120V or 240V electrical

service.

When more power is necessary, mobile power supplies can be used.

These units come with wheels so that they can be

rolled where needed.

These units also operate on 120V or 240V electrical

service and can provide up to 6,000A of ACor half-wave DC.

M ti Fi ld I di t

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Magnetic Field Indicators

Determining whether a magnetic field is of adequatestrength and in the proper direction is critical whenperforming magnetic particle testing. There is

actually no easy-to-apply method that permits anexact measurement of field intensity at a given pointwithin a material. Cutting a small slot or hole into thematerial and measuring the leakage field thatcrosses the air gap with a Hall-effect meter isprobably the best way to get an estimate of theactual field strength within a part. However, sincethat is not practical, there are a number of tools andmethods that are used to determine the presence

and direction of the field surrounding a component.

H ll Eff t M t (G M t )

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Hall-Effect Meter (Gauss Meter)

As discussed earlier, a Gauss meter is commonlyused to measure the tangential field strength on the

surface of the part. By placing the probe next to thesurface, the meter measures the intensity of the fieldin the air adjacent to the component when amagnetic field is applied. The advantages of this

device are: it provides a quantitative measure of thestrength of magnetizing force tangential to thesurface of a test piece, it can be used formeasurement of residual magnetic fields, and it canbe used repetitively. The main disadvantage is that

such devices must be periodically calibrated.

Pi G

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Pie Gage

The pie gage is a disk of highly permeable material divided intofour, six, or eight sections by non-ferromagnetic material (suchas copper). The divisions serve as artificial defects that radiateout in different directions from the center. The sections arefurnace brazed and copper plated. The gage is placed on thetest piece copper side up and the test piece is magnetized.After particles are applied and the excess removed, theindications provide the inspector the orientation of the magneticfield. Pie gages are mainly used on flat surfaces such as

weldments or steel castings where dry powder is used with ayoke or prods. The pie gage is not recommended for precisionparts with complex shapes, for wet-method applications, or forproving field magnitude. The gage should be demagnetizedbetween readings.

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Slotted Strips

Slotted strips are pieces of highly permeable

ferromagnetic material with slots of different widths.

These strips can be used with the wet or dry method.

They are placed on the test object as it is inspected. The

indications produced on the strips give the inspector ageneral idea of the field strength in a particular area.

M i P i l

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Magnetic Particles

The particles that are used for magnetic particle inspection are a

key ingredient as they form the indications that alert the inspectorto the presence of defects.

Particles start out as tiny milled pieces of iron or iron oxide. Apigment (somewhat like paint) is bonded to their surfaces to givethe particles color.

The metal used for the particles has high magnetic permeabilityand low retentivity.

High magnetic permeability is important because it makes theparticles attract easily to small magnetic leakage fields from

discontinuities, such as flaws.Low retentivity is important because the particles themselvesnever become strongly magnetized so they do not stick to eachother or the surface of the part.

Particles are available in a dry mix or a wet solution.

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Dry Magnetic Particles

Dry magnetic particles can typically be purchased in red, black,

gray, yellow and several other colors so that a high level ofcontrast between the particles and the part being inspected can

be achieved. The size of the magnetic particles is also very

important.

Dry magnetic particle products are produced toinclude a range of particle sizes.

The fine particles have a diameter of about

50 mwhile the course particles have a

diameter of 150 m(fine particles are more than 20 times lighter

than the coarse particles). This makes fine particles more

sensitive to the leakage fields from very small discontinuities.

Color contrast coatings are available in several colors, including

blue, red, gray, and black.

Th ti l h i l i t t

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The particle shape is also important.

Long, slender particles tend align themselves along

the lines of magnetic force.

However, if dry powder consists only of elongatedparticles, the application process would be less than

desirable since long particles lack the ability to flowfreely.

Therefore, a mix of rounded and elongated particles

is used since it results in a dry powder that flows welland maintains good sensitivity.

Most dry particle mixes have particles with L/D ratios

between one and two.

Wet Magnetic Particles

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Wet Magnetic Particles

Magnetic particles are also supplied in a wet suspension such as wateror oil. The wet magnetic particle testing method is generally moresensitive than the dry because the suspension provides the particles withmore mobility and makes it possible for smaller particles to be used (the

particles are typically 10 mand smaller) since dust and adherence tosurface contamination is reduced or eliminated.

The wet method also makes it easy to apply the particles uniformly to arelatively large area.

Wet method magnetic particles products differ from dry powder productsin a number of ways. One way is that both visible and fluorescentparticles are available. Most non-fluorescent particles are ferromagneticiron oxides, which are either black or brown in color.

Fluorescent particles are coated with pigments that fluoresce whenexposed to ultraviolet light.

Particles that fluoresce green-yellow are most common to takeadvantage of the peak color sensitivity of the eye but other fluorescentcolors are also available.

Also, both visible and fluorescent wet suspended particles are availablein aerosol spray cans for increased portability and ease of application.

S f C

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Summary of Technique Choices

It is obvious that there are many options and choices

to consider when developing the most suitable

technique for the part to be inspected. In order to

provide the optimum inspection approach, some of

the key areas to be evaluated include:Material type

Part configuration

Dimensions

Surface condition

Type and location of discontinuities anticipated

Code and specification requirements

Customer-specific requirements

O th k th h i f t h i

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Once these are known, the choice of technique canbe made. These key items should be considered:

Type of current (AC, HWDC, FWDC)

Wet suspension or dry particles

Visible or fluorescent particles

Direct or indirect magnetization Continuous or residual

Stationary or portable equipment

The best combination can be determined throughqualification by validation through the use ofcontrolled test specimens.

There are many variables to consider when deciding upon the

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There are many variables to consider when deciding upon thebest inspection technique for a particular application. A listing ofsome of the considerations and options follows.

Considerations

Customer requirements - specifications, standards, ordrawing requirements

Equipment availability - AC/DC, stationary, portable, black

light, etc.AC power availability - needed for all except permanent

yokes or magnets

Part size requirements - e.g., will it fit into a wet horizontalunit?

Part location - will it require portable equipment?

Types of discontinuities anticipated - orientation and location

Retentivity of test material - must be high if residualtechnique is to be used

Options

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Options

AC or DC (HWDC or FWDC) Magnetizing Current

Use AC for surface discontinuities or those that would beexpected during in-service inspection.Use DC for deeper penetration and possible detection ofslightly subsurface discontinuities.

Continuous or ResidualUse the residual technique for inspection of highly retentivematerials, especially where large batches are to be inspected.Use the continuous technique for all other applications,especially where higher sensitivity is required.

Wet or Dry Particle Application

Wet particles have better mobility, but generally lowerpermeability. Use wet for small surface discontinuities orservice-induced discontinuities. Use dry for slightly subsurface

discontinuity detection.

Color Contrast or Fluorescent Particles

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Color Contrast or Fluorescent Particles

Color contrast does not require a darkened viewing area orblack light illumination, however, the sensitivity will belower than that of fluorescent particles. Use color contrast

for field inspections where highest sensitivity is notrequired. Use fluorescent where maximum sensitivity isessential.

Stationary, Mobile, or Portable Units

In a production or maintenance facility, the versatility of thewet horizontal unit makes it the ideal choice; however,many applications involving immovable or large testobjects eliminate this possibility, resulting in the need for

mobile or portable units.

Amperage to be Used

Will be determined based on specification and standard

requirements and the test part dimensions.

Amperage Selection

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Amperage Selection

Many international standards give tables of current valuesbased on the type of currentavailable in the magnetizing

equipment, the sensitivity required, and the componentgeometry and material. In the absence of a specified standard,the following general rules of thumbhave been widely used.

For direct circular magnetization of basically round sections use

a range of 300800 amps per inch diameter (1232 amps/mm).This is usually 500 amps per inch (20 amps/mm) based onpeak value for full-wave rectified current. Values above 500amps/inch diameter (20 amps/mm) are only recommended forlow-permeability materials or for slightly subsurface

discontinuity detection.

Example 1.

For a 1.5 inch diameter bar, 9 inch long, 1.5 inch 500 ampsper inch = 750 amps.

For central conductor circular magnetization of

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For central conductor circular magnetization ofhollow round components with conductor barplaced concentrically with the component, the

same current values stated above would apply,based on the outer diameter or inner diameter,depending on which surface is to be examined.

Example 2:

Tubular component, 2 inch outside diameter, 1.5inch inside diameter, using a 1 inch diametercentral conductor (looking for OD discontinuities),2 inch outside diameter 500 amps per inch =

1000 amps.

Dry Particle Inspection

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Dry Particle Inspection

In this magnetic particle testing technique, dry particles are

dusted onto the surface of the test object as the item ismagnetized.

Dry particle inspection is well suited for the inspections

conducted on rough surfaces. When an electromagneticyoke is used, the AC current creates a pulsating magneticfield that provides mobility to the powder.

Dry particle inspection is also used to detect shallow

subsurface cracks.

Dry particles with half wave DC is the best approach wheninspecting for lack of root penetration in welds of thin

materials.

Steps for performing dry particles inspection:

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Steps for performing dry particles inspection:

Surface preparat ion - The surface should be

relatively clean but this is not as critical as it is withliquid penetrant inspection. The surface must befree of grease, oil or other moisture that could keepparticles from moving freely. A thin layer of paint,

rust or scale will reduce test sensitivity but cansometimes be left in place with adequate results.Any loose dirt, paint, rust or scale must beremoved.

Some specifications require the surface to be coatedwith a thin layer of white paint in order to improve thecontrast difference between the background and theparticles (especially when gray color particles are used).

A l i th t i i f U

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Apply ing the magnet iz ing force - Use

permanent magnets, an electromagnetic yoke,

prods, a coil or other means to establish the

necessary magnetic flux.

App ly ing dry magnet ic part ic les - Dust on a

light layer of magnetic particles.

Blowing of f excess powder - With the

magnetizing force still applied, remove the

excess powder from the surface with a few

gentle puffs of dry air. The force of the air needsto be strong enough to remove the excess

particles but not strong enough to remove

particles held by a magnetic flux leakage field.

T i ti th t i i f If the

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Term inating the magnet izing force - If the

magnetic flux is being generated with an

electromagnet or an electromagnetic field, the

magnetizing force should be terminated. Ifpermanent magnets are being used, they can

be left in place.

Inspect ion for indicat ions - Look for areaswhere the magnetic particles are clustered.

Wet Suspension Inspection

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Wet Suspension Inspection

Wet suspension magnetic particle inspection, more commonlyknown as wet magnetic particle inspection, involves applying

the particles while they are suspended in a liquid carrier. Wetmagnetic particle inspection is most commonly performed usinga stationary, wet, horizontal inspection unit but suspensions arealso available in spray cans for use with an electromagneticyoke.

A wet inspection has several advantages over a dry inspection.First, all of the surfaces of the component can be quickly andeasily covered with a relatively uniform layer of particles.Second, the liquid carrier provides mobility to the particles foran extended period of time, which allows enough particles tofloat to small leakage fields to form a visible indication.Therefore, wet inspection is considered best for detecting verysmall discontinuities on smooth surfaces. On rough surfaces,however, the particles (which are much smaller in wetsuspensions) can settle in the surface valleys and lose mobility,rendering them less effective than dry powders under these

conditions.

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Steps for performing wet particle inspection:

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Steps for performing wet particle inspection:

Surface preparat ion - Just as is required with dry

particle inspections, the surface should be

relatively clean. The surface must be free of

grease, oil and other moisture that could prevent

the suspension from wetting the surface andpreventing the particles from moving freely. Any

loose dirt, paint, rust or scale must be removed.

Some specifications require the surface to be coated

with a thin layer of white paint when inspecting using

visible particles in order to improve the contrast

difference between the background and the particles

(especially when gray color particles are used).

Apply ing suspended magnet ic par t ic les - The

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Apply ing suspended magnet ic par t ic les Thesuspension is gently sprayed or flowed over thesurface of the part. Usually, the stream ofsuspension is diverted from the part just before the

magnetizing field is applied.Apply ing the magnet iz ing force - The

magnetizing force should be applied immediatelyafter applying the suspension of magnetic

particles. When using a wet horizontal inspectionunit, the current is applied in two or three shortbusts (1/2 second) which helps to improve particlemobility.

Inspect ion for indicat ions- Look for areas wherethe magnetic particles are clustered. Surfacediscontinuities will produce a sharp indication. Theindications from subsurface flaws will be lessdefined and lose definition as depth increases.

Light Requirements When Using Visible Particles

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Light Requirements When Using Visible Particles

Visible particles inspections can be conducted usingnatural lighting or artificial lighting. However, sincenatural daylight changes from time to time, the use ofartificial lighting is recommended to get better

uniformity.

Artificial lighting should be white whenever possible

(halogen lamps are most commonly used).

The light intensity is required to be 100 foot-candles(1076 lux) at the surface being inspected.

Light Requirements When Using Fluorescent Particles

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g q g

Ultraviolet Lighting

When performing a magnetic particle inspection using fluorescentparticles, the condition of the ultraviolet light and the ambient white lightmust be monitored. Standards and procedures require verification oflens condition and light intensity. Black lights should never be used witha cracked filter as the output of white light and harmful black light will be

increased. Also, the cleanliness of the filter should also be checkedregularly. The filter should be checked visually and cleaned asnecessary before warming-up the light.

Most UV light must be warmed up prior to use and should be on for atleast 15 minutes before beginning an inspection.

For UV lights used in component evaluations, the normally acceptedintensity is 1000 W/cm2 at 38cm distance from the filter face. Therequired check should be performed when a new bulb is installed, atstartup of the inspection cycle, if a change in intensity is noticed, or

every eight hours of continuous use.

EVALUATION OF TEST RESULTS AND REPORTING

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EVALUATION OF TEST RESULTS AND REPORTING

The evaluation of test results is the most critical stage in themagnetic particle inspection process and greatly relies on the

qualifications of the inspector.

The ability of an inspector to observe an indication dependsupon the correct application of the proper techniques, andusing equipment and accessories that are functioning correctly.

Another consideration is the inspectors ability to perform thetest correctly. Competence should have previously beendemonstrated by satisfying qualification requirements.

The qualification process should also include a visionexamination to prove visual acuity and ability to distinguish thecolors associated with the MT technique to be used.

Classification of Indications

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Once detected, the indications should be classified as

either false,nonrelevant,or relevantbefore final

evaluation.

False Indications

False indications can be produced by improper handling and do not relate to

the partscondition or use. An example is magneticwriting.This is typicallyproduced by the formation of indications at local poles that are created whenthe part comes in contact with another magnetized part prior to or duringinspection. This can be eliminated by demagnetization and repeating theinspection.

Magnetic writing is most likely to occur when using the residual method,through poor handling that allows the individual parts to touch. The continuoustechnique may require the demagnetization of parts before the next inspectionto preclude the possibility of magnetized components touching. This type offalse indication can be eliminated through careful handling.

Other sources of false indications may be caused through the use ofexcessively high magnetizing currents or inadequate precleaning of the parts toremove oil, grease, corrosion products, and other surface contaminants.

Nonrelevant Indications

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o e e a t d cat o s

These are the result of flux leakage due to geometrical orpermeability changes in the part.

Examples of geometric causes include splines, thread roots,gear teeth, keyways, or abrupt section changes.

A concern with these conditions is that they may also be stressrisers and could be the origin for fatigue-induced cracks.

These conditions are therefore some of the most critical; thepossibility that one of these nonrelevant indications can conceal

a crack must be considered.

Other potential sources of nonrelevant indications includelocalized permeability changes in the part, which may be due tolocalized heat treatment or variations in hardness, and may

also occur at the fusion zone of a weld.

Relevant Indications

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Relevant Indications

These are produced by flux leakages due to

discontinuities in the part.

When these discontinuities are not in compliance

with a code, they are classified as rejectable.

If they meet the acceptance criteria they areconsidered to be acceptable discontinuities.

Discontinuities that do not permit the part to be usedfor its original purpose or can potentially cause the

part or fail are classified as defects.

Reporting

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Reporting

When the parts have been inspected and all

indications evaluated, it will be necessary to preparea report detailing the results of the test and, ifapplicable, the size, location, and orientation ofdiscontinuities found. This report may varyconsiderably from company to company, but as aminimum, it should meet customer requirements andshould typically include the following data:

1. Contract and customer

2. Inspection company

3. Date of inspection

4. Inspectorsname and qualification and certificationlevel

5. Report number or identification

6 Applicable codes specifications or procedures

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6. Applicable codes, specifications, or procedures,including type and technique of inspection

7. Acceptance criteria

8. Component description, part number, and serialnumber

9. Flux line direction with respect to discontinuityorientation

10. Other identification details as requested in thecontract; for example, batch or order number.

11. Material batch number (particles, liquid carrier,

etc.)12. Results of inspection, including recording ofindications as detailed below

13. Signature or inspection stamp of inspector

APPLICATIONS

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APPLICATIONS

The magnetic particle test method is effective forthe detection of surface and slightly subsurface

discontinuities in ferromagnetic parts. It can be

used as an inspection tool at all stages in the

manufacture and end use of a product.

Primary Processing

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y gWhen the original material has become solid, it must be workedand formed to produce a rough shaped product. During theseprocesses, the part is said to be in its primary processingstage. Typical primary processes include, forging, casting,rolling (hot and cold), extrusion, and drawing. During theseprocessing operations, discontinuities may be produced orexisting discontinuities may be modified. Examples of primaryprocessing discontinuities detectable by magnetic particletesting include:

Forging burstsForging laps

Rolling laps, seams, and stringers

Rolling seams

Laminations (at the edges of plates and sheets)Casting shrinkage (at the surface)

Casting inclusions (at the surface)

Casting cold shuts (at the surface)

Casting hot tears (at the surface)

Secondary Processing

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Secondary Processing

After rough shaping the metal in the primaryprocessing stage, it is further refined and shaped to

produce finished products. This stage is referred toas secondary processing and can include suchprocesses as machining, grinding, plating, and heattreatment. These secondary processes may also

produce discontinuities or change the appearance ofexisting ones. Examples of secondary processingdiscontinuities detectable by magnetic particletesting include:

Quench and heat cracksGrinding cracks (or checks)

Machining tears

Plating cracks

Welding

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Welding

When parts are joined together by a welding

process, numerous discontinuities may be created.

Examples of the welding processes are found inChapter 2. The following is a list of welding related

discontinuities that may be detected by magnetic

particle testing when at or close to the surface.Cracks (longitudinal, transverse, and crater)

Lack of fusion

Incomplete penetration (if accessible)Entrapped slag

Inclusions

Overlap or coldlap

Service

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Service

When the part is put into service and subjected to

stresses and environments that may be

detrimental to its structure, service discontinuities

may result. Those that are detectable by

magnetic particle testing include:

Fatigue cracks

Stress corrosion cracks

Static failure cracks (overstressed structures)

Types of ComponentsE l f t i l t t d t th t b i t d i th

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Examples of materials, structures, and parts that may be inspected using themagnetic particle test method include:

Ingots

Billets

SlabsBlooms

Bar stock

Sheet

Rod

Wire

Castings

Shafts (plain, threaded, or splined)

Welds

Bearings and bearing races

Nuts and bolts

GearsCylinders

Discs

Forgings

Tubular products

Plate

Industrial Sectors

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Industrial Sectors

Magnetic particle testing has many applications

throughout industry including but not limited to thefollowing sectors:

Petrochemical

ConstructionAircraft and aerospace

Automotive

DefenseNuclear

Transportation

Shipping (marine)

Advantages

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g

The following are advantages of magnetic particle testing as compared toalternative NDT methods.

1. Test results are virtually instantaneous, in that indications will form within one

ortwo seconds of particle application. No developing or processing times areinvolved.

2. Permanent records of indications can be produced using photography,magnetic rubber, or transparent tape techniques.

3. MT can be applied in-situ, without the need for an AC power supply, by

using permanent magnets or battery-powered yokes.4. Indications are easy to interpret.

5. The indications formed by the particles closely represent the shape and typeof the discontinuity.

6. Training and experience requirements prior to becoming certified aresignificantly less stringent than for UT, RT, or ET, since MT is a relatively simple

process.7. MT equipment can be much less expensive than other NDT equipment.Depending on the degree of automation or scale of operation, it may also bemore economical than many other NDT methods.

8. Virtually any size or shape of component can be inspected.

9. Inspections can be performed during all stages of manufacturing.

10. Test part surface preparation is less critical than with penetrant testing.

11. MT can be used to inspect through metallic andt lli ti l ti ith t h i It

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p gnonmetallic coatings or plating with some techniques. Itshould be noted, however, that a reduction in sensitivitywill occur as the thickness of the coating increases.Maximum coating thickness should be established throughqualification tests or stipulated in customer specificationsor code requirements.

12. There are no known personnel hazards associatedwith the process because the magnetic fields generated

are of short duration; however, the usual electric shock,manual lifting, and chemical (petroleum distillate)precautions apply. Additionally, the parts may becomeheated during the process if high-amperage current isapplied for an extended period.

13. Many parts can be inspected simultaneously if usingthe residual magnetism technique.

14. MT can be automated for certain production lineapplications.

Limitations

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Limitations

The following are limitations of magnetic particle testing as compared toother NDT methods.

1. It is only effective for the examination of ferromagnetic materials.2. Discontinuity detection is limited to those at or near the surface.

3. Demagnetization may be required before, between, and afterinspections.

4. Discontinuities will only be detected when their major axis interruptsthe primary flux lines. This necessitates inspection in more than onedirection to assure discontinuity detection regardless of orientation.5. Some magnetic particle testing techniques may cause damage to thepart as a result of arcing or localized overheating of the parts (forexample, when using DC prods).

6. Paint and/or coating removal is necessary from localized areas on the

part to facilitate good electrical contact when using direct magnetizationtechniques.

7. Uniform, predictable flux flow through the parts being tested may notbe possible due to complex shapes.

8. Nonrelevant indications due to abrupt changes in component profileor local changes in material properties may make interpretation difficult.

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Examples

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Crane Hook with

Service Induced Crack

Fluorescent, Wet Particle Method

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Gear with



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Splined Shaft with

Service Induced Cracks


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Large Bolt with



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Lack of Fusion in SMAW Weld

Visible, Dry Powder Method

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Toe Crack in SMAW Weld


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Throat and Toe Cracks in

Partially Ground Weld

Movies links

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http://www.youtube.com/watch?v=4P3DzZzXwa8

http://www.youtube.com/watch?v=N1emHJD0-1E

http://www.youtube.com/watch?v=T_7LZ3lZFJ0http://www.youtube.com/watch?v=dQoB7jpxSe8
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END

ndt lecture12 2015

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