Training on NDT

8/8/2019 Training on NDT

1/22

Introduction to Non-Destructive Testing

Codes & Standards of NDT:

American National Standards Institute (ANSI)

ANSI is the primary organization that is responsible for coordinating the activities ofall other standard writing organizations. ANSI primarily reviews and certifiesthat the standards are correct. ANSI has established specific guidelines for theformation of other standard bodies such as ASME and AWS. Recently, several ANSIpiping standards (B31.1, B31.3, B31.4 and B31.8) have been reclassified as ASMEdocuments.

American Society of Mechanical Engineers (ASME)

ASME Codes are among the most widely used in the petrochemical industry and theygovern items such as pressure vessels, boilers, and piping.

The following is a list of the ASME Codes

ASME Code B31.1 ASME Code B31.3 ASME Code B31.4 ASME Code B31.8 ASME Boiler and Pressure Vessel Code, Section I ASME Boiler and Pressure Vessel Code, Section IV ASME Boiler and Pressure Vessel Code, Section V ASME Boiler and Pressure Vessel Code, Section VIIIASME Code B31.1- Power Piping

Pertains to the design, materials, fabrication, test, and inspection of power andauxiliary piping. Typical systems include steam, water, gas, oil, and air servicesthat support electric power generation. Refer to pages A1 through A8 of theAddendum for a more detailed explanation of the scope of ASME Code B31.1.

ASME Code B31.3 - Chemical Plant and Petroleum Refinery Piping

Pertains to the design, materials, fabrication, test, and inspection of chemical pipingsystems. Typical applications include on-plot stripping steam, crude oil, acid, caustic,sour water, and cooling systems that are used to refine petroleum products. Refer topages A14 and A15 of the Addendum for a more detailed explanation of the scope ofASME Code B31.3.

ASME Code B31.4 - Liquid Transportation Systems for Hydrocarbons, Liquid

Petroleum Gas, Anhydrous Ammonia, and Alcohols

Pertains to the design, construction, inspection, testing, operation, andmaintenance of liquid petroleum and anhydrous ammonia piping systems. Typicalapplications include off-shore and off-plot cross-country pipelines, terminals,and tank farms. Refer to pages A39 and A40 of the Addendum for a more detailedexplanation of the scope of ASME Code B31.4

ASME Code B31.8 - Gas Transmission and Distribution Piping Systems


2/22

Pertains to the design, fabrication, installation, inspection, testing, and operationof gas transmission and distribution systems (including gas pipelines), gascompressor stations, and gas metering and regulating stations. Refer to pages A51and A52 of the Addendum for a more detailed explanation of the scope of ASMECode B31.8.

ASME Boiler and Pressure Vessel Code, Section I - Power Boilers

Pertains to the design, material selection, fabrication, inspection, testing, andcertification of power boilers that exceed 15 psi for steam service and that exceed160 psi and/or 250oF for hot water service. Refer to page A60 of the Addendum for amore detailed explanation of the scope of ASME Section I.

ASME Boiler and Pressure Vessel Code, Section IV - Heating Boilers

Pertains to the design, material selection, fabrication, inspection, testing, andcertification of heating boilers that do not exceed 15 psi for steam service or that donot exceed 160 psi and 250oF for hot water service. Refer to page A67 of theAddendum for a more detailed explanation of the scope of ASME Section IV

ASME Boiler and Pressure Vessel Code, Section V - Nondestructive Examination

Provides requirements and methods for NDT that include radiographic,ultrasonic, liquid penetrant, magnetic particle, eddy current, visual examination,leak testing, and acoustic emission. Refer to page A74 of the Addendum for a moredetailed explanation of the scope of ASME Section V.

ASME Boiler and Pressure Vessel Code, Section VIII - Pressure Vessels

Pertains to the design, material selection, fabrication, inspection, testing, andcertification of pressure vessels. The three classes of pressure vessels that arecovered by this code are welded, forged, and brazed. Typical applications includesteam generators, heat exchangers, hydrocrackers, fractionation towers, reformerreactors, and other components that are designed to contain fluids or vapors athigh temperatures and pressures. Refer to pages A77 and A78 of the Addendumfor a more detailed explanation of the scope of ASME Section VIII.

American Society for Nondestructive Testing (ASNT)

ASNT is an organization that is dedicated to NDT. ASNT organizes and distributestechnical information that is specific to NDT.

ASNT SNT-TC-1A - Recommended Practice for Personnel Qualification andCertification in Nondestructive Testing

Provides requirements for the qualification and certification of NDT personnel.

American Welding Society (AWS)

The AWS is an organization that provides standards for the welded fabrication ofstructures and bridges with structural steel and sheet metal.


3/22

AWS D1.1 - Structural Welding Code

Provides acceptance standards and welding requirements for buildings,bridges, and tubular structures. The requirements for the qualificationof weld procedures and welders also are included in this Code.

American Petroleum Institute (API)

API 510 API 620 API 650 API RP-2AAPI 510 - Pressure Vessel Inspection Code

Provides requirements for the maintenance inspection, repair, alteration, andrerating procedures for pressure vessels that are used by the petroleum and chemicalprocess industries. Refer to page A118 of the Addendum for a more detailedexplanation of the scope of API 510.

API 620 -Design and Construction of Large, Welded, Low-Pressure Storage Tanks

Pertains to the design and construction of large, low pressure, above groundstorage tanks. Typical applications include the storage of gases or vapors that resultsfrom refining operations. Refer to page A123 of the Addendum for a more detailedexplanation of the scope of API 620.

API 650 - Welded Steel Tanks for Oil Storage

Provides material, design, fabrication, and testing requirements for above groundatmospheric tanks. Typical applications include the storage of crude and otherliquid petroleum products. Refer to page A130 of the Addendum for a more detailedexplanation of the scope of API 650.

API RP-2A - Recommended Practice for Planning, Designing, and Constructing FixedOff- Shore PlatformsProvides a guide for the design and construction of drilling platforms. Refer to pageA139 of the Addendum for a more detailed explanation of the scope of API RP-2A

NONDESTRUCTIVE

TESTING:

PURPOSE,

ADVANTAGES,

ANDIMPORTANCE

The purpose of nondestructive testing (NDT) is to prevent the prematurefailure ofcomponents or weldments and to improve the reliability and the safetyof production and maintenance operations at the manufacturing facil i ty . NDT isused during fabrication and construction, as well as maintenance repair activities, tocheck and to monitor the condition of equipment that is used in all aspects of oilextraction andrefining.


4/22

NDTisanimportant toolthatallowstheusertofindpotential problemsthatcouldresultin an unexpected failure of piping, vessels, or other components during normaloperation. When a problem is found, it can be fixed before a situation developsthat could result in personnel injury, equipment orproduction loss, or damage to theenvironment.

The role of the Engineer who is responsible for the design, maintenance, oroperation ofmechanical systems is torecognizewhenNDTcanbeusedandshould beused to ensure or to improve the safety, quality, and reliability of Companyfacilities and equipment

The following examples are of how NDT can be used in mechanical inspectionprocessesto improvequality,reliability, andsafety:

1. Tocheck the integrity ofpipelines or vessels thatcontain flammableor toxicSubstances

2. To determine the effects of erosion and corrosion onpipelines, components, andstoragetanks.

3. To identify cracks or weak areas that result from cyclic stresses during normal orsevereserviceconditions.

4. Toobserve operatingcharacteristics ofequipment orsystems

NDT improves reliability through the detection of potential problems that couldresult inpremature system or component failures. Nondestructive tests areperformed

before the first installation, after repairs, and at regularly scheduled intervalsthroughout the life of critical components. The continuous performance ofNDT atregularly scheduled intervals provides an added level of confidence in the continuedreliability of the component or system on which theNDT isperformed. Becausecomponents that are tested through use ofNDT are not destroyed and can stillbeused after they are tested,NDT is more cost effective than any type of destructive

testing. Defects that are identified through use ofNDT during the fabrication of asystemcostlessto repairthandefects thatmustberepairedinthefieldafterthesystemisoperational The capability of NDT to identify discontinuities has also led to anincrease in the initial quality of fabrications and repairs. When aperson whofabricates or repairs a component is aware that the fabrication or the repair willbesubjected toNDT, thatperson is more likely to correctly perform the fabrication orrepairbecauseheknows that theNDTwill identifyany discontinuities.

Importance

NDT can be an extremely effective tool to inspect and to examine systems andcomponents;

however, a solid understanding of theprinciples of the variousNDT methods is

required to properly use NDT. By understanding the basic principles of thevarious NDT methods, an Engineer will be able to determine the most

appropriate NDT method for a given test scenario. Not all of theNDT methods

areequallyeffective. SomeNDTmethods are only capable ofsurfaceexaminations;

otherNDTmethods canexamine theentirevolume ofwelds

or components. SomeNDT methods cannotbe used on nonferrous materials, and

stillother methods are not conducive to extremely corroded or rough surfaces.


5/22

BaseMetalDiscontinuities

A discontinuity is an interruption of the typical structure of a material such as alack ofhomogeneity in the mechanical, metallurgical, orphysical characteristics ofthe material or weldment. Base metal discontinuities areclassified in accord with

the point in the manufacturing process in which such discontinuities occur.

These discontinuities are classified asfollows:

Inherent

PrimaryProcess

SecondaryProcess

Inherent

Inherent discontinuities result from the original melt, casting, or solidification of the

ingotofprimarymetaloralloy.

Primary Process

Primaryprocess discontinuities are formed during the rough shaping and forming ofmetals duringprimaryprocessing such as forging, casting, rolling and drawing

Secondary Process

Secondary process discontinuities are associated with final finishing operationssuch as machiningandheattreatments.

WeldMetalDiscontinuities

Figure 1 shows cracks in welds. Cracks can be either longitudinal (aligned withthe weld bead)or transverse(perpendicular to theweldbead)and theycanoccur fromstresses that are developed during the welding process.Cracks also can be eithersurface or subsurface. Cracks severely reduce the strength of a weld. Welds withcracksarenotreliable. Onlyvery small cracks areacceptable,andsuchcracksareonlyacceptableinnon-critical applications.

Figure 2 shows slag inclusions. Slag inclusions are located within a weld and

they occurwhen gases, impurities, or flux contaminate a slag weld.Slag inclusionsdo not always present aseriousproblemunlesstheyareverylargeoriftherearemanysmallinclusionsina given area. Slaginclusionsweakenthewelds.

Figure3showslackoffusion. Lackoffusiongenerallyislocatedattheweldmetalandbase metal interface and it occurs when the molten weld metal does not completelyfuse with an adjacent weldbeadorwith thebasematerial. Lackof fusionwillalmostalwaysbeclassified as adefect because theweldisnotreliable.


6/22

Figure 4 shows incomplete root penetration. Incomplete root penetration occurswhen the weldmetaldoesnotcompletely penetrate intotherootareaandconsume both

basematerials. Incomplete rootpenetration creates a weak area in the weldment andis unacceptable in critical applications.

Figure5showsweldundercut. Weldundercutisanareainwhichtheactual weldislessthan thespecificcontour. Undercutting resultsinadepression onthesurfaceatthepointat which the weld metal contacts the base metal. As the size of the undercutincreases, the effective cross-sectional area of thebase metal is reduced and causes adecreaseinthestrengthof the base metal.

Figure6showscold lap. Coldlapoccurs when theweldmetalfreezes tooquicklyanddoes notfusewiththesurfaceofthebasemetal. Coldlapismosttypically foundonthecoverpass at thetoeoftheweld.

Figure 7 shows root concavity. Root concavity occurs in weldjoints that are weldedfromone side only, an example of which wouldbepipe.

The following are typical causes of root concavity:

1. Toomuchheat,whichcauses shrinkage

2. Arootopeningthatistoowide

3. Insufficient deposits ofweldmetal

Figure 8 shows a craterpit. Craterpits are located on the weldbead surface and aregenerally associated with Gas Tungsten Arc Welding (GTAW). Crater pits resultfrom the rapid breaking of the electric arc so that the weld puddle freezes tooquickly and shrinks, which leaves asmallvoid.

Figure 9 shows an arc strike.Arc strikes are caused by dragging the electrode overthe surface of the base metal in an effort to initiate an arc for welding.Suchstrikes that are within the weld groove are generally acceptable as long as the arc is

properly preparedandis fullyconsumed intheweld.

Figure 10 shows weldporosity. Weld porosity is caused by inadequate flux orshielding gas coverage, which allows oxygen to contaminate the molten weld metal

prior to solidification. The porosity can be located on the weld surface but istypically located within the weld. Moisture or other contaminants, such as oil, thatare on thebase metal also can vaporize during weldingandcanresultingasbubbles

beingtrappedintheweldmetal.

Defects

Adefect inacomponent oraweld isadiscontinuity orflaw thatwouldprobablyresultinan earlyfailureofthecomponent orweld. Because alldiscontinuities arenotdefects,acceptance criteria mustbe established to identify which discontinuities are acceptable.Past experience has helped to establish the criteria for an acceptable discontinuity.These criteria are known as acceptance criteria and they can be found in theapplicable fabrication and construction codes and standards.The discontinuities must

be compared to the acceptance criteria to determine whethertheyactuallyaredefects.

For example, 1/16" of weld undercut in material that is 1" thick would not be


7/22

acceptable inpiping that iscoveredbyASMEB31.1 (referenceparagraph136.4.2),butsuch an undercut would be acceptable in structural materials that are covered byAWS D1.1 (reference paragraph 8.15.1.5). Also, 1/8" of weld reinforcement on a

pipinggirthweldwitha3/8"wall thickness wouldbe acceptable on an ASME B31.3piping system; however, such a weld reinforcement would notbe acceptable on anASMEB31.1pipingsystemwithamaximum design temperature thatisabove75oF.

IDENTIFYIN GTHECODES,STANDARDS,PROCEDURES,AND

INSTRUCTIONS ASSOCIATE DWITHNONDESTRUCTIV ETESTING

American National Standards Institute (ANSI

ANSIistheprimary organization thatisresponsible forcoordinating theactivities ofallotherstandard writing organizations. ANSIprimarily reviews and certifies that thestandards are correct. ANSI has established specific guidelines for the formation ofother standard bodies such as ASME and AWS. Recently, several ANSI pipingstandards(B31.1,B31.3, B31.4and B31.8) havebeenreclassified asASMEdocuments.

American Society of Mechanical Engineers (ASME

ASME Codes are among the most widely used in thepetrochemical industry and theygovern items such aspressure vessels, boilers, andpiping.

The following is a list of the ASME Codes

ASMECodeB31.1ASMECodeB31.3ASMECodeB31.4ASMECodeB31.8ASMEBoilerandPressureVessel Code,SectionIASMEBoilerandPressureVessel Code,SectionIV

ASMEBoilerandPressureVessel Code,SectionVASMEBoilerandPressureVessel Code,SectionVIII

ASME Code B31.1 -PowerPiping,pertains to the design, materials, fabrication,test, and inspection ofpower and auxiliarypiping. Typical systems include steam,water, gas, oil, and air services that support electric power generation. Refer to

pages A1 through A8 of the Addendum for a more detailed explanation of the scopeof ASMECode B31.1.

ASME Code B31.3 - ChemicalPlant andPetroleum Refinery Piping,pertains to thedesign, materials, fabrication, test,and inspection of chemical piping systems. Typicalapplications include on-plot stripping steam, crude oil, acid, caustic, sour water, andcooling systems that are used to refinepetroleumproducts. Refer topages A14 andA15 of the Addendum for a more detailed explanation of the scope of ASME CodeB31.3.

ASME Code B31.4 - Liquid Transportation Systems for Hydrocarbons, LiquidPetroleum Gas, Anhydrous Ammonia, and Alcohols, pertains to the design,construction, inspection, testing, operation, and maintenance of liquidpetroleum andanhydrous ammonia piping systems. Typical applications include off-shore andoff-plot cross-country pipelines, terminals, and tank farms. Refer topagesA39andA40 of the Addendum for a more detailed explanation of the scope of ASME Code


8/22

B31.4.

ASME Code B31.8 - Gas Transmission andDistribution Piping Systems,pertainsto the design, fabrication, installation, inspection, testing, and operation of gastransmission and distribution systems (including gaspipelines), gascompressorstations,

and gas metering and regulating stations. Refer to pages A51 and A52 of theAddendum for a more detailed explanation ofthescopeofASMECodeB31.8.

ASME Boiler and Pressure Vessel Code, Section I -PowerBoilers,pertains tothe design, material selection, fabrication, inspection, testing, and certification of

power boilers that exceed 15psi for steam service and that exceed 160psi and/or250oF for hot water service. Refer topage A60 of the Addendum for a more detailedexplanation of thescopeofASME SectionI.

ASME Boiler and Pressure Vessel Code, Section IV -HeatingBoilers ,pertainsto the design, material selection, fabrication, inspection, testing, and certification ofheatingboilers that do not exceed 15psi for steam service or that do not exceed 160

psi and 250oF for hot water service. Refer to page A67 of the Addendum for a

more detailed explanation of the scope ofASMESectionIV.

ASME Boiler and Pressure Vessel Code, Section V -Nondestructive Examination ,provides requirements and methods for NDT that include radiographic, ultrasonic,liquid penetrant, magnetic particle, eddy current, visual examination, leak testing,and acoustic emission. Refer topage A74 of the Addendum for a more detailedexplanation of thescopeofASME SectionV.

ASME Boiler and Pressure Vessel Code, Section VIII - Pressure Vessels,pertains to the design, material selection, fabrication, inspection, testing, andcertification ofpressure vessels. The three classes of pressure vessels that arecovered by this code are welded, forged, and brazed. Typical applications includesteam generators, heat exchangers, hydrocrackers, fractionation towers, reformer

reactors, and other components that are designed to contain fluids or vapors at hightemperatures and pressures.Refer to pages A77 and A78 of the Addendum foramoredetailedexplanation ofthescopeofASMESectionVIII.

American Society for Nondestructive Testing (ASNT)

ASNT is an organization that is dedicated toNDT. ASNT organizes and distributestechnical information that is specific toNDT. For example, ASNT developed themanual thatisused asthesupplemental textforthiscourse.

ASNT SNT-TC-1A - Recommended Practice for Personnel Qualification andCertification in Nondestructive Testing,provides requirements for the qualification andcertification ofNDTpersonnel.

American Welding Society (AWS)

The AWS is an organization thatprovides standards for the welded fabrication ofstructures andbridges with structural steel and sheet metal. For thepurpose of thiscourse,onlyAWS D1.1,theStructural Welding Code,willbereferenced.

AWS D1.1 - Structural Welding Code, provides acceptance standards andwelding requirements for buildings, bridges, and tubular structures. The


9/22

requirements for the qualification of weld procedures and welders also areincluded in this Code. Typical applications include structural steel for catwalks,landings,andbuildings.

American Petroleum Institute (API)

API510API620API650APIRP-2A

API 510 - Pressure Vessel Inspection Code, provides requirements for themaintenance inspection, repair, alteration, and reratingprocedures forpressure vesselsthatareusedby the petroleum andchemical process industries. Refer topageA118oftheAddendum foramore detailed explanation ofthescopeofAPI510.

API 620 -Design and Construction ofLarge, Welded, Low-Pressure Storage Tanks,pertains to the design and construction of large, lowpressure, above ground storagetanks. Typical applications include the storage of gases or vapors that results from

refining operations. Refer to page A123 of the Addendum for a more detailedexplanation ofthescopeofAPI620.

API 650 - Welded Steel Tanks for Oil Storage , provides material, design,fabrication, and testing requirements for above ground atmospheric tanks. Typicalapplications include the storage ofcrudeandotherliquidpetroleumproducts. Referto

pageA130oftheAddendum foramoredetailedexplanation ofthescopeofAPI650.

API RP-2A - Recommended Practice for Planning, Designing, and ConstructingFixed Off- Shore Platforms ,providesaguidefor thedesignandconstruction ofdrillingplatforms. Refer to pageA139oftheAddendum foramoredetailedexplanation of thescopeofAPIRP-2A.

Determining TheAppropriateApplicationOfNondestructive TestingMethodsEVALUATIN G THE CAPABILITIES AND LIMITATION S OF VISUAL WELD EXAMINATIONS

Purpose - The purpose of a visual weld examination (VT) is to detect visible surfacediscontinuities ona weldment. VT is themost frequentlyusedmethod ofexamination,

and welders and welding inspectors continuously use VT during welding operations tomakebetterqualitywelds. VT often will identifyproblemsduringwelding thatcanberepaired in process to prevent the discovery of a discontinuity by a subsequentnondestructive test.

Advantages - VT is thequickestand mostcost-effective method ofNDT foruse in theidentification ofa surface discontinuity on a weld.Because the VT method ofNDTrequires the fewest technical and interpretive skills, VT also is the simplestNDT


10/22

method to learn. The use of VT throughout the welding process significantlyimproves the success of subsequent NDT and reduces thecostofrepairs.

Examination Requirements

The tool that is used to perform VT is the human eye. The following are therequirements fortheperformance ofVT:

Visual Acuity - Personnel who perform VT must pass an annual eyeexamination in accordance with industry standards. The eye examination checksfor conditions such as visual acuity, color blindness, and depth perception.

Distance - The examiners eye shouldbe located within 24 inches and at anangleof not less than 30 degrees to the surface of the weld that isbeing examined toconduct a direct visual examination. Mirrors can be used to improve theangleofvision.

Access - If the area tobe examined is not directly accessible, an examination aidcanbeused. Examination aidsarecoveredlaterinthisModule.

Lighting - A flashlight or other additional lighting should be used to sufficientlyilluminate the area that is tobe examined. A minimum of 35 foot candles of lightshould be available for normal visual weld examinations. When performing VTfor small indications, a minimum of 50 foot candles of light should be available. Ifrequired by procedure, a light meter can be used to determine theexactamountofillumination thatisavailable.

Examination Aids

Examination aids sometimes are used to facilitate visual examinations. Thefollowing are examples ofcommonly usedvisual examinationaids:

MirrorsPortableLightingFlashlightsLightMetersStraightEdgesandRulersMagnifying LensesBoroscopesMicroscopes

VideoCamerasWeldGages

When the use of examination aids (such as boroscopes) is necessary to performremote examinations, the image resolution must be at least equal to the imageresolution that is attainable bydirectvisualexamination.

Several types of weld inspection gages are available to simplify the measurements ofcomplex weld configurations when conducting VTs.


11/22

The following are some of the gauges that are generally used:

Cambridge Gage - This gage can measure undercut, weld reinforcement, bevel angle,rootopening, filletweldsize,andjointmismatch.

GAL Hi-Lo Gage - This gage can measure joint mismatch, root opening, and weldreinforcement.

AWSTypeGage -Thisgagealsocanmeasure various sizesofstandard filletwelds.CommonApplications

Thefollowingarecommon applications forvisualweldexaminations

Todeterminethesizeandlengthoffilletweldsonstructuralmembers

To inspect the weld joint fit-up including bevel angle, root opening, land,andcleanliness ofpipingwelds.

Toinspectin-processweldsandcompletedweldspriortoadditionalNDT.

Toinspecttheproperfit-upofsocketweldfittingsonsmalldiameterpipe.

The following are the common discontinuities that can be detected during avisual examination:

Cracks

Slag

Porosity

Undercut

ColdLap

ArcStrikes

EVALUATIN GTHECAPABILITIESANDLIMITATIONSOFLIQUID

PENETRANTTESTING

The Purpose - The purposeofliquidpenetranttesting(PT)istodetectdiscontinuities onthesurfaceofnon-porousmaterials.

Advantages

Read the Introduction to Lesson 2 in the ASNT Manual. The introduction describesthe followingmajoradvantages ofPT:


12/22

Goodsensitivity

Inexpensive

Simple

Widerangeofuses

Principles ofLiquidPenetrant Testing(PT)

PT uses theprinciple of capillary action to detect discontinuities. When a liquidpenetrant is appliedtothesurfaceofamaterial, capillary actionwillcausethepenetrantto enterany small openings that exist on the surface of the material.After the excess

penetrant is removed, a developer is applied to the surface of the material to draw theabsorbed penetrantback out of theopenings. If the application of thedevelopercausesthepenetrant tobe drawnback out of an opening, discontinuities arepresent on thesurfaceof thematerial

PT activity canbebrokendownintothefollowingbasic steps:

Cleanthesurface.

Applythepenetranttothesurfacethatistobeinspected.

Remove theexcesspenetrant

Applyadeveloper.

CommonApplications

Themostcommon useofPT is tocheckweldssuchassocketweldsand

rootpasses onpressure vessels, storage tanks, andpiping systems. PTalso is thebest

method for use in the identification of surface discontinuities on non-magnetic

materials, such as aluminum andstainlesssteel. PTalsocanbeusedonmagnetic steelswhen magnetic particle testing cannot beperformed. The Applications section that

begins onpage 2-17 of the ASNT Manualprovides additional information on the

applications ofPT.

Limitations

Themajorlimitation ofPTisthatitcannot detectsubsurface discontinuities. Becauseofthis limitation, PTisnotasufficientNDTformanycriticalweldmentsinwhichthevolume of the weld must be examined. PT also is not conducive to high

temperature applications and special penetrants anddevelopersarerequiredforeven

moderatetemperature use. PT is performed on materials that have a maximum

temperature of 125oF.Because surface coatings block discontinuity openings,another limitation of PT is that it cannot beperformed on surfaces that are covered

withpaintorwith othercoatingmaterials. ThelengthyPTdwelltime,sometimesup


13/22

to45minutes,canlimitits application.

CommonDiscontinuities

Surface cracks, porosity, undercut, and cold laps are the most common discontinuitiesthatare detectedby PT.Although these discontinuities are open to the surface, the

size of the discontinuity canbe too small to allow detectionby VT; therefore, PT isused. PT ismore sensitive thanVTonsmall,tightimperfections.

EVALUATIN G THE CAPABILITIES AND LIMITATIONS OF MAGNETIC PARTICL E

TESTING

Thepurposeofmagnetic particle testing (MT) is todetect discontinuities thatareopentothe surfaceornearthesurfaceofferromagnetic materials.

Ferromagnetic materials (e.g., iron, steel, and associated alloys) are those materialsthatcanbe strongly magnetized. Paramagnetic materials (e.g., sodium metal) can

be slightly magnetized anddiamagnetic materials (e.g.,copper)cannotbemagnetized.

Advantages

A major advantage of MT is that, for most applications , MT uses portable testequipment that is relatively simple to use.When compared to PT, MT also has thefollowing advantages:

MTislesslaborintensive

Aftertheinitialinvestment, MTislessexpensivetoperform

MTcandetectsomesubsurface defects.

MThaslessposttestclean-up

Principles ofMagnetic Particle Testing(MT)

Magnetic particle testing isbased on theprinciple of magnetism. Magnetism is theability of one ferromagnetic material to attract other ferromagnetic materials.Magnetic fields exist within andaround apermanentmagnet oraround aconductorthatcarriesanelectriccurrent. These magnetic fields are made up of magnetic lines offorce that are perpendicular to the direction of the electric current flow. When a

discontinuity existsinaferromagnetic material, the discontinuity results in a distortionin the magnetic lines of force and creates a leakage field in which the magnetictestingparticles are gathered. The visual gathering of magnetic particles indicatesthatadiscontinuity mayexistinthematerialthatisbeingtested.

Method:

Anelectric current ispassed through a test object to create a magnetic field inthetestobject(i.e.,thetestobjectismagnetized).


14/22

Magnetic particles areappliedtothesurfaceofthemagnetized testobject

Thetestobject isevaluatedforgatheredmagneticparticles

TestEquipment

Various kinds of test equipment are used to establish the magnetic field in the testobject. Portable yokes and prods that are most commonly used during fabricationand construction of petroleum extraction and refining facilities. Large stationaryequipment is mostly used in manufacturing andproduction facilities because thesefacilities require continuousMT.

Thefollowingmethods areused toestablishthemagnetic field:

Indirect Method - This method uses an electromagnetic yoke topass a magnetic fieldthrough the testobject. The testobjectcompletesamagneticcircuitwith the yoke thatresults in the establishment of a magnetic field in the test object. Yokes can use AC,HalfWave(HW)DC,orDCcurrenttoestablishmagnetic fields.

Direct Method - This method usesprods topass electrical current through the testobject.The current thatpasses through the test object establishes the magnetic field.Prods also can use AC, HWDC, or DC current to establish magnetic fields.

TheuseofACcurrentresultsinamagnetic fieldthatisfairlyshallowinthetestaterial;the useofDCcurrentprovidesadeepermagneticfield. However, DCcurrentalsohasmoreofa tendency topermanently magnetize thetestobjects.

TypesofMagnetic Particles andMethodsofApplication

Magnetic particles canbe suspended in liquid or they canbe in the form of a drypowder. Themethod ofapplication depends onthetestsituation. Thefollowingmethods

canbeused:

The wet method uses magnetic particles that are suspended in a liquid such asoil orwater.The magnetic particles maybe fluorescent or non-fluorescent. The mixtureisappliedbyallowingittoflowoverthetestobject.

The dry method uses magnetic particles in the form of a drypowder.Themagneticparticles are non-fluorescent, but the particles are available in different colors.Theparticles are appliedby allowing them to lightly settle on the surface of the testobject. Theparticles mustbeappliedlightlyandevenly tothesurface.

Stress corrosion cracking inpressure vessels consists of micro cracks that are notvisible to the human eye and which are usually undetectable using dry magnetic

particle testing. However, through use of wet fluorescent MT, the stress corrosioncracking can be reliably detected. The wet method of magnetic particle testinggenerallyprovides a more sensitive inspectionbecause thewetmethod isabletodetectminutediscontinuities.

CommonApplications

Magnetic particle testing is used to inspect carbon steel weldments, socket welds onpiping, weld bevel preps, structural fillet welds, valve bodies, shafts of rotatingequipment, pump impellers, machined parts,vessels, andstoragetanks. TheuseofMT


15/22

isparticularly important for vessels and tanks that are susceptible to sulfide stress andhydrogeninducedcracking.

Limitations

The major limitations of MT are that it can onlybe used to find defects that arenear the

surface of ferromagnetic materials, and thatMTcanmagnetize thecomponentthat is under test. MTwillnotfinddeep-seateddiscontinuities; however, thislimitationisprimarily based on whetherACorDCcurrentisusedandthetypeofmagnetic particlethatisused.


The most common discontinuities that are found by MT are surface or near-surface cracks, porosity, undercut,andcoldlap.

EVALUATING THE CAPABILITIE S AND LIMITATION S OFULTRASONIC

TESTING

Thefollowingaretheprimarypurposesofultrasonic testing(UT):

Todetectsurfaceandsubsurfacediscontinuities inmetallicmaterials

Tomeasurethethicknessofmetallic materials

UT, unlike thepreviously discussed methods ofNDT, canbe used to inspect theentire volumeofthetestobject.

Advantages

The following advantages of UT make it a widely used method of testing fordefects in a varietyofsituations:

UTisextremelysensitive

UTdisplaysthesizeandlocationofdiscontinuities

UTcanbeusedonalmost anytypeofmetallicmaterial

UTcanbeusedonallbuttheverycomplexweldments

UTonlyrequiresaccesstoonesideofthetestobject.

UTcanbeperformedthroughuseofportable equipment.

UTissafetoperform.

Principles ofUltrasonic Testing(UT)

UT is a more complex method ofNDT than is VT, PT, or MT. UT uses apulsegeneratortogenerateanelectricalsignalthatissuppliedtoa transducer. The transduceruses this electrical signal to generate and emit ultrasonic energy. The ultrasonic energy


16/22

causes mechanical vibrations (wavepropagation) that are in the form of a sound wavethat travels through a test object. After the wave travels through the test object, thetransducer receives the returnsignal andsends it throughaprocesscircuit. Theoutputof the process circuit is sent to a cathode ray tube. If the wave encounters adiscontinuity inthe test object, thereturnsignalwillreflectthedisruption ofthewave.The ability of the ultrasonic system to detect small defects (e.g., the sensitivity) is afunction ofthewavelength oftheemittedultrasonic energy.

Whenultrasonicenergy (sound wave)istransferred intoamaterial, thedistancethatthewave travels canbe determined through use of an oscilloscope. If the wave does notencounter a discontinuity, only the initial and return signals appearon the oscilloscopescreen. However, if the wave encounters a discontinuity, part of this energy isreflected back and three indications (initial signal, return signal, and reflected signal)willappearon theoscilloscope screen. A qualified inspector can determine theapproximate size and the location of the discontinuity fromtheseindications.

TestEquipment

Thefollowingarethebasictestequipment components thatareusedtoperformUT

Transducer - This device is used to convert energy from one form to another form.As illustrated in Figure 5, UT typically uses piezoelectric devices that deliverstraight or angle ultrasonic beams to detect discontinuities in test objects. Thesedevices (transducers) are usedboth to transmit and receive ultrasonic signals.

Couplant - A couplant is a medium that is used to facilitate the transmissionofultrasonic energybetween the transducer and the test object.

Pulse Generator and Oscilloscope - Thepulse generator is used to generate theinputelectrical signal to the transducer and the oscilloscope is used to display the return

signalonacathode ray tube (CRT).

Other important pieces of test equipment are calibration blocks and referenceblocks. Calibration and reference blocks are used to help ensure that the testequipment isproperly operating. Because the operation of the test equipment candirectly affect the inspectors interpretation of the testresults,properoperationof thetestequipment isextremelyimportant

Additionally, hand held ultrasonic thickness gages also use the contact testingmethod toprovide spot thickness determination. Ultrasonic thickness gagesprovide adigital display of the material thickness and are capable of storing large quantities ofthicknessdata.

CommonApplications

Amajorapplication ofUT is thicknessgagingforcorrosiondetection. UT also isusedto inspect the integrity of weldbevelprep areas, fullpenetration butt welds, and platematerial

Limitations

Because of the many variations of testing methods, UT is the least limited method of


17/22

NDT. However, thefollowing limitations doexist:

UTcanonlybeperformedbyhighlyskilledtechnicians

UTcannot beusedonveryroughsurfaces withoutsurfacepreparation

UTcannot always beusedoncourse grainmaterials(castings).

UTcannotdetectdiscontinuities thatareparalleltotheultrasonic beam

UTcannot beusedtochecksomeweldjointconfigurations (i.e.,socket welds).


UT canbe used to detect both surface and subsurface discontinuities. All of thebasemetal andwelddiscontinuities like cracks, porosity, undercut, incomplete penetration,lack of fusion, slag, and root concavity or convexity. Another commondiscontinuity that is identified through use of UT is an unacceptable decrease inwall thickness thatisduetoerosionorcorrosion.

EVALUATIN G THE CAPABILITIES AND LIMITATION S OF RADIOGRAPHIC TESTING

The purpose of radiographic testing (RT) is to detect surface and subsurfacediscontinuities in variousmaterials.

Advantages

The following are the advantages of RT, and these advantages are similar to theadvantages of UT:

RTisextremelysensitive

RTcanidentifybothsurfaceandsubsurface discontinuities

RTcanbeusedonawidevarietyofmaterials.

RT provides a permanent record that shows the size and locationofdiscontinuities.

RTcanbeusedthroughuseofportableequipment

Principles ofRadiographic Testing(RT)

RT uses radioactive sources (x-ray, gamma ray, or neutron beams) to emit photonsthat penetrate the test object. The energy and wavelength characteristics of these

photonsallow them tobeused topenetrateanymaterial. The physicalcharacteristics of


18/22

the test object determines the amount of the energy beam that passes through thematerial. Any changes in material thickness or density will affect the amount ofenergy that passes through the test object. The portion of the photons that passthrough the test object are used to expose a special type of film. The image that is

produced on the film will show any changes in the density of the areas that areexposed to the penetrating radiation.

SourcesofRadiation

Radiation is the energy that is given off due to a nuclear reaction at the atomic level.This energymaybe in the formofanelectromagnetic waveoraparticulate. Photons,which are small packets of energy that are caused by radioactive decay, displaybothwaveandparticle characteristics.

X-RayMachine

Cobalt60

Iridium192

X-raysaregenerated inelectronic X-raytubesof the linearaccelerator type. The tubesmaybeportable toallowperformance ofradiographic examinations inthefield.

The sources of gamma rays are the disintegrating nuclei of radioactive isotopes.

The followingaretheradioactive isotopesthat are usestoproducegammarays:

Iridium-192 (Ir-192)

Cobalt-60 (Co-60)

DangersofRadiation

Thepenetrating nature of radiographic rayspresents a danger topeople.These rayspass through thebody in the same way in which theypass through the test objectand, if the exposure is excessive, the rays can cause permanent damage to thehuman body. A significant danger exists when sources of radiation are notproperlyhandled. This danger is magnified by the fact that there are no immediate signsthat tell people that they are being exposed to harmful amounts of radiation.Overexposure to radiation may cause radiation sickness, permanentdamage tovital

bodyorgans or,insevere cases,death.

Because of these dangers, specialprecautions and safetyprocedures mustbe strictly

followed by personnel who handle radiation sources. Ionizing Radiation ProtectionRules for a Radiographic Inspection Company, sets the general guidelines that allpersonnel must follow to protect themselves against ionizing radiation. Thisinstruction is usedbypersonnel who are involved in all aspects ofstorage,handling,anduseofradioactive sources.

RadiationMonitoring

Because the senses of the human body cannot detect the presence of radiation,


19/22

special monitoring equipment must be used. Personnel Monitoring Equipment,identifies devices that are used to measure the actual exposure ofpersonnel during the

performance of RT. These devices include filmbadges, dosimeters, and radiationsurvey meters.A radiation survey meter is used to check radiation levels in a given area.Thisinformation is needed to determinepersonnel stay times and shielding requirements.

Radiation Safety

The following are the basic radiation safety techniques that are used to reducepersonnel exposure toionizingradiation:

Time-Astheamount oftimethatisspentneararadiationsource decreases, theexposuretotheradiationdecreases.

Distance - As the distance from a radiation source increases, the exposure totheradiation decreases.

Shielding-Astheamount ofshieldingthatisbetweentheradiationsource andpersonnelincreases,theamount ofexposure decreases

The following are the most important factors that must be considered in the

achievement ofthehighest qualityimage:

Thetype,position, andintensity oftheradiation source

Thethickness, density,andconfiguration ofthetestobject

Thetypeandpositionofthefilm.

Filmprocesstimeandchemical temperatures

FilmQuality

Apenetrameter is used to check the quality of the image that isproduced on theradiographic film. Apenetrameter is typically a wire orblock that is made from thesame material as the test object. The dimensions of thepenetrameter are critical

because the dimensions represent the thickness of the object that isbeing examined.The penetrameter is used to confirm the sensitivity of the radiograph. The

penetrameter is not used to determine the size of discontinuities. Thepenetrameterimage isapermanent recordthatproves thatthe technique that is used toperform theRT produced a good quality radiograph. . ASTM wire type penetrameters and hole

typepenetrameters are commonly used.

CommonApplicationsThemajorapplication ofRT istoexamine criticalfullpenetration weldsin

piping andpressure vessels for discontinuities. Critical welds require a high degreeof confidence because of thepotential hazards that are associated with their failure.RT is an effective waytoachievethisconfidence.

Ingeneral,RTandUTareusedforsimilarapplications. RTalsoisusedto evaluatethe


20/22

effectsoferosionandcorrosiononcomponent andpipingwallthickness

Limitations

Thefollowingarethemajorlimitations fortheuseofRT:

RTonlycanbeperformedbyhighlyskilledtechnicians

RTcannot detect discontinuities thatareperpendiculartotherays.

RTexposes personnelwhoareintheareatoradiation

ThefollowingconditionsmaylimittheuseofRT:

Weldjointgeometry

Accessibility

Because RT that is performed on piping or vessels that contain fluid does notproduce acceptableresults,another limitation is thatpipingsystems andvesselsmustbedrainedprior to theperformance of RT. Alsoaccess isneeded toboth sides ofobject

beingradiographed (source ononeside,filmontheother).


RTisusedtofindbothsurfaceandsubsurface discontinuities. Allofthebasemetalandweld discontinuities are commonly detected through use ofRT. Thesediscontinuities

include cracks, porosity, undercut, incomplete penetration, lack of fusion, slag,tungsten inclusions, and root concavity and convexity.

EVALUATINGTHECAPABILITIE SANDLIMITATIONSOF

ELECTROMAGNETI CTESTING

The purpose of electromagnetic testing (ET) is to detect surface and limitedsubsurface discontinuities in various materials or to measure material properties(such as coating thickness) by checking for changes in eddy currents or magneticfields thataregenerated in thetestobject.

Advantages

The major advantage of ET is that the testing methods canbe specialized to covera wide range of applications. For example, magnetic flux leakage techniques areextensively usedon ferromagnetic materials; eddy current testing can be used onany material that conducts electricity. Otheradvantages areasfollows:


21/22

ETcanproduceindications thatareproportional tothesizeofthediscontinuity.

Principles ofElectromagnetic Testing (ET)

Electromagnetic induction is the basis for the operation of electric generators,motors,

transformers, and electromagnetic testing. Electromagnetic induction is theabilitytoinduce a current into an adjacent object. ET uses alternating current that ispassed through a test coil to induce current into a test object. These inducedcurrents are closed loopcurrentsandtheyareknownaseddy currents. Eddycurrentsareperpendicular to themagnetic fields. ETmeasures thechanges in the impedance ofthetestcoilthatresults from thechanges in theflowofeddycurrents. Thechanges intheflowofeddycurrentsare caused bydiscontinuities inthetestobject. Eddycurrentscannot begeneratedwithaninput ofdirectcurrent.

Asignificantfactor in theability toperformET is themagnetic permeability of the testobject. Magnetic permeability is a measure of the magnetic tendency (ferromagnetic,

paramagnetic, ordiamagnetic) ofamaterialand,becauseeddycurrentsareinducedbyamagnetic field, the magnetic permeability of the test material will have a strong

influence on the eddy current response.

TestEquipment

The specific test equipment that is needed toperform ET depends on the specific testmethod; however, allETrequiressometypeofoscillator(togenerate accurrent), acoil,an impedance detector, and a display unit.ET equipment comes in a variety ofshapes, sizes, and arrangements thatdepend ontherequirements ofthespecifictest.

CommonApplications

ET is a very specialized method ofNDT and is commonly used for the

following reasons:

Toinspectheatexchangertubes

Toperformmagneticfluxleakagetestingofferromagnetic materials

Tocheckdryfilmcoatingthicknessoflinedpipes.

Tocheckmaterialthicknesses.

Limitations

The major limitation of ET is that it will only find discontinuities that arewithin approximately one half inch of the surface. The equipment that is required to

performET is very sophisticated and, as with UT and RT, ET also requires highlyskilled technicians to analyze theresults



22/22

ET can be used to find discontinuities in welds and base metals; therefore, thediscontinuities are the same as those discontinuities that are identified by the othermethodsofNDT. These discontinuities includecracks, incompletepenetration (on thinmaterials), andlackoffusion

SPECIALIZE DTESTINGMETHODS

InfraredInspection

Infraredinspectionusesaspecialcamera (scanningradiometer) thatcapturesrealtimeheat variation data from an electron beam to produce a heat sensed picture(thermogram) that shows theamount ofheatthatisbeingradiatedfromacomponent.

Infrared inspections areused tomonitor forheat loss in the following equipments :

BoilersFurnacesStacksBearingsElectrical switchgearandconnectorsTransformersElectricmotorsCryogenicstoragetanks

HolidayDetector

Protective coatings are used to prevent corrosion in many piping systems andcomponents. Damage to theseprotective coatings can result in a corrosion problem.Small cracks or pinholes that are in a protective coating are called holidays. Aspecial device that iscalled aholidaydetector iscommonly used tocheck the integrityofprotective coatings. The holiday detector works through application of anelectric charge to the pipe wall. After the charge isapplied, thepipe is checked forgrounds. The existence of grounds or arcs indicates thepresence of a defect in the

protective coating. The testequipment thatis usedfordetectiondepends onthespecificapplication.

Acoustic Emission

Acoustic Emission (AE) uses techniques that are similar to UT.Sound waves arepassed through a test object that is subjected to stress to check for discontinuities. Asdiscontinuities develop, they emit mechanical vibrations that can be identified by

the AE transducer. AE is used to check for defects in composite materials, such asfiberglass or plastic. The common defects that are found by AE include cracks,voids, and laminations.

Training on NDT

Documents

Transcript of Training on NDT