Guide to Pigging - ELEKOMS · 2020. 7. 11. · 1. Purpose of Pigging S e c t i o n I 1.0 Introduction. There are four basic reasons to pig a pipeline: A. Cleaning: Lines are cleaned

TDW Pigging Products & Services

Guide to Pigging

© Copyright 2011All rights reserved.

T.D. Williamson, Inc.

NOTICE

Any operation involving work on pipe containing

liquids or gases under pressure is potentially hazardous.

It is necessary, therefore, that correct procedures be

followed in the use of any equipment to maintain a safe

working environment.

This publication is not intended to replace product

manuals. Please see the appropriate product manuals

for complete instructions/procedures.

P.O. Box 3409Tulsa, OK 74101- 3409 USA

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Fax (918) 446-6327E-mail: [email protected]

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® Registered trademark of T.D. Williamson, Inc. in the United States and foreign countries.

ii

TABLE OF CONTENTS

SECTION I: PURPOSE OF PIGGING

1.0 Introduction .........................................................................................1

2.0 Cleaning ..............................................................................................1

3.0 Batching ..............................................................................................2

4.0 Displacement .......................................................................................3

5.0 Internal Inspection ................................................................................3

SECTION II: PIPELINE DESIGN CONSIDERATIONS

1.0 Introduction .........................................................................................5

2.0 Pipeline Design for Pigging ....................................................................5

SECTION III: PIG LAUNCHING AND RECEIVING TRAPS

1.0 Introduction .........................................................................................9

2.0 Launch and Recovery Procedures ...........................................................10

3.0 Sample Pigging Systems.......................................................................15

SECTION IV: SELECTING THE RIGHT PIPELINE PIG

1.0 Introduction ........................................................................................17

2.0 Pig Selection.......................................................................................18

SECTION V: PIGGING NEW CONSTRUCTION

1.0 Introduction ........................................................................................23

2.0 Selecting the Pig .................................................................................23

3.0 Propelling the Pig ................................................................................24

SECTION VI: ONSTREAM PIGGING OF NATURAL GAS LINES, NATURAL GAS LIQUIDS AND REFINED PETROLEUM PRODUCTS

1.0 Introduction ........................................................................................29


3.0 Speed ................................................................................................31

4.0 Frequency ...........................................................................................32

5.0 Performance .......................................................................................32

SECTION VII: ONSTREAM PIGGING OF CRUDE OIL LINES

1.0 Introduction ........................................................................................33


3.0 Pigging Speed .....................................................................................35

4.0 Frequency ...........................................................................................35

5.0 Performance .......................................................................................36

iii

SECTION VIII: INLINE INSPECTION TECHNOLOGY

1.0 Introduction ........................................................................................37

2.0 Preparing the Line ...............................................................................37

3.0 Inline Inspection ..................................................................................38

4.0 Survey Selection .................................................................................38

5.0 Geometry Inspection ............................................................................39

6.0 Metal Loss Inspection ..........................................................................41

7.0 Seam Weld Inspection and Other Longitudinally Oriented Anomalies ...........43

8.0 Geometry, Metal Loss, Long-Seam, Longitudinal, Hard Spot Inspection .......44

9.0 Crack Inspection .................................................................................46

10.0 Pipeline XYZ Mapping ...........................................................................46

11.0 Leak Detection and Location .................................................................49

12.0 Survey Results ....................................................................................50

SECTION IX: Maintenance, Cleaning and Storage of Pigs and Components

1.0 Introduction ........................................................................................53

2.0 Maintenance .......................................................................................53

3.0 Cleaning .............................................................................................53

4.0 Storage ..............................................................................................55

Appendix I:

Pipeline Pigging Questionnaire .......................................................................57

Appendix II:

Inline Inspection Questionnaire ......................................................................61

Appendix III:

Useful Conversion Factors .............................................................................67

Appendix IV:

Common Acronyms .......................................................................................69

• 1

Purpose of Pigging

S e c t i o n I

1.0 Introduction

Therearefourbasicreasonstopigapipeline:

A. Cleaning:Linesarecleanedtoimproveflow(throughput)andtocontrolinternalcorrosion.

B. SeparatingProducts(Batching):Pigsareofteninsertedbetweentwodissimilarproductstoavoidmixing.Thisisreferredtoasbatchpigging.

C. Evacuation(Displacement):Pigsareusedtodisplaceoneproducttypewithanother.Forexample:Inanewconstructionapplication,theairisdisplacedwithwater,thewaterisdisplacedwithairandthepipedried;thedryairisdisplacedwithnitrogenortheprimaryproducttobemovedthroughthepipeline(oil,refinedproductsorgas).

D. InternalInspection:Federallawrequirespipelineownerstoperiodicallyinspecttheirpipelines.SeeSectionVIIIformoreinformation.MostpipelineoperatorsarerequiredtoimplementanIMP(IntegrityManagementPlan).MostIMP’sincorporatetheuseofinternalinspectionpigs.Theseinspectionpigscomeinavarietyofshapesandsizeswitheachprovidingdatawhichdetectsdents,buckles,metallossandcracking.

2.0 Cleaning

2.1 Increase Pipeline Flow Efficiency

Pigsareruntomaintainlineefficiency.Anydecreaseinpipelineefficiencyreducesthethroughputofapipeline,leadingtolostrevenue.Theimportanceofoperatingathighefficiencyisillustratedbythefollowingexamples:

A. Aonepercentincreaseinefficiencyofanaturalgaspipelinetransporting100millioncubicfeetaday(2.8millioncubicmeters)canincreasethroughputbyonemillioncubicfeetaday(.028millioncubicmeters).

B. Athreepercentincreaseinefficiencyofacrudeorproductpipelinetransporting50,000barrelsaday(135,950cubicmeters)canincreasethroughputby1,500barrelsaday(4,078.5cubicmeters).

Itisdifficulttomakeapipeline100percentefficient.Frictionandotherphysicalfactorsreduceflow.Inanaturalgastransmissionline,compressoroverflowoil,corrosiveelements,millscale,dust,distillate,andcondensationcanformtocoattheinsideofthepipe.Paraffinandsandbuildupincrudelines,increasedliquidsinmultiphasegaslines,andsolidsbuildupinproductlinespresentsomewhatthesameproblem.Inallcases,thecontaminationbuildupincreasesresistancetoflowwhichdecreasespipelineefficiencyorincreasescostoftransmission.

Flow,pressuredrop,andoperatingcostarefactorsusedtodeterminelineefficiency.Shouldalineneedcleaning,apigisinsertedintothestreamtocleanthepipewall,therebyincreasingflow.Figure1showsacleaningpigbeingloadedintolauncher.

Fig 1. Loading a Cleaning Pig

• 2

2.2 Corrosion Control

Pigsareusedtoimproveandmaintaininternalpipecleanlinessbyremovingcontaminatesanddepositsonthepipewall.Periodiclinecleaningwithpigscanremovemanyofthecorrosiveelements.Pigscanalsobeusedwithchemicalcorrosioninhibitorstomitigatetheeffectsofcorrosion.Forexample,aspecialtypigcandistributecorrosioninhibitorontotheinsideofthepipewallsasshowninFigure2.

Corrosivesituationswhichcanberemedied,atleastinpartbypigging,include:

A. Waterandotherfluidswhichsettleoutofgas,crude,orproductsduetoinsufficientflowvelocityforentrainment,intermittentflow,orpressure/temperaturerelatedsolubilitychanges.Thesefluidscancontainoxygen,hydrogensulfide,carbondioxide,chlorine,salts,acidsandothercorrosives.

B. Loosesediment,includingcorrosionproducts,scale,sandanddirt,whichusuallypromoteformationoflocalcorrosioncellsonapipe’sbottomquadrant,especiallyinconjunctionwithconditionslistedabove.

C. Corrosionproductssuchaswaxorothersoliddepositsadheringtothepipewallcanshieldcorrodingareas,therebylimitingeffectivenessofothercorrosionmitigationmeasuressuchaschemicalinhibition.

3.0 Batching

Themixingoftwoproductsastheyarepumpedthroughthelineissometimesreferredtoascontamination.Thereareatleastthreesourcesthatcreatethiscontaminationinaproductspipeline,namely:

A. Flowregime

B. Pipelinedesign

C. Operatingprocedures

Whencontaminationoccursbetweentwoproducts,themixturemustbehandledinsomemanner.Themostfrequentoccurrenceistocutoutthemixtureandre-blenditwithoneofthetwoproductsoranotherproductbeingcurrentlyhandled.

Topreventcontamination,abatchingpig,showninFigure3,isinsertedintothestream,eitherattheinterfaceoratthebeginningandendofabufferbatchwhichisinsertedbetweenthetwoproducts.Whentheproductarrivesatthefinalterminal,contaminationandre-blendingareminimal.

Fig 3. OptionAll™ Batching Pig

Fig 2. V-Jet® Corrosion Inhibitor Pig

• 3

4.0 Displacement

Hydrostatictestinginvolvespurgingasectionofpipelineofallair,fillingitwithwater,andthenpressurizingthelinetoaspecifiedtestpressureforsomeperiodoftime.Uponcompletionofthetest,thewaterisremovedsothelinecangoon-stream.

Displacementpigsareusedtodisplaceairaheadofthehydrostatictestwater,andtodisplacewaterafterthehydrostatictest.

Displacementpigsarealsousedtodisplaceahazardoushydrocarbonmaterialwithaninertgastoperformfieldrepairs.AbidirectionaldisplacementpigisshowninFigure4.Insomecases,multi-cuppedandfoampigscanalsobeusedfordisplacement.

5.0 Internal Inspection

Internalinspectionpigs,sometimesreferredtoas“smartpigs,”areusedtodetectpipeanomalieswhichmayresultinpipefailure,lossoflife,andpropertydamage.RefertoSectionVIIItogainabetterunderstandingofinlineinspection(ILI)pigtechnology.

Fig 5. Magnetic Flux Leakage Tool (Smart Pig)

Fig 4. 24-inch Displacement Pig for Bidirectional Applications

• 5

Pipeline Design Considerations

S e c t i o n I I

Fig 6. Radius

1.0 Introduction

Pipelinesshouldbedesignedtoensureatrouble-freepiggingoperation.Basically,apipelineneedsaconsistentopenborefromstarttofinishifitistobepiggedsuccessfullyandconsistently.Indesigningapipelinetobepigged,thefollowingshouldbeconsidered:

• Lengthofpigrun

• Bendradiusanddegreeofbend

• Valvetype

• Pigpassageindicators

2.0 Pipeline Design for Pigging

2.1 Length of Pig Run (Distance between Launching and Receiving Traps)

Thedistancebetweenpigtrapsisoftendeterminedbyeitherthepumpstationlocations,naturallengthofpipeline,and/ortheavailabilityofasitecapableoflaunchingandreceivingpigs.Thefollowingaremaximumrecommendeddistancesforgivenproducttypes.Theserecommendeddistancesarebaseduponapigbeingabletotraverseadistanceinagivenproductandremainrelativelyeffectivethroughoutthelength.Naturalgaslines,duetothenatureofadrygascontain-ingsandormillscale,tendtobemostabrasive,causingpigstowear-outmorequickly.Crudeoilpipelinesofferanaturallubrication,prolongingthelifeofpigs.

A. 100miles(160km)forgaspipelines.

B. 150miles(240km)forproductlines.

C. 200miles(320km)forcrudeoillines.

2.2 Bends

A. BendRadiusisdefinedas:thearclengthtakenfromtheradiuspointtothecenterofthebend,measuredinpipediameters.SeeFigure6.

B. Eachpigisdesignedtotraverseacertainminimumradiusbend.Onepigmaytraversea1.5DR-90degreebend;anothermaytraversea1.5DR-45degreebendwhileathirdmayonlytraversea3DR-90degreebend.Itiscommontofind1.5DRbendsinnaturalgaslines,3DRbendsinliquidsystems,andpossibly1DRbendsinsmallrefinerypiping,Abendhastwoidentifyingcomponents:1)Bendradius2)DegreeofBend.

C.DegreeofBendisdefinedastheanglechangeindirectionofthepipe,measuredindegrees.ThedegreeofbendinFigure6is90degrees.Mostpigswillnottraverse1DRbendsnormiterbends.Examplesoftypicalbendsinclude:

• Tees

• Laterals

• Pipeinsidediameter

• Dualdiameterlines

• 6

• 1.5DRBend:A1.5DRelbowhasabendradiusequalto1.5timesthenominalpipediameter.A1.5bendina12”pipelinewouldhaveabendradiusof18”andisshowninFigure7.

• 3DRBend:A3DRelbowhasabendradiusequalto3timesthenominalpipediameter.A3DRbendina12”pipelinewouldhaveabendradiusof36”,asshowninFigure8.

• FieldBend:Afieldbendisabendconductedinthefieldduringthepipelineconstruction.Thisisnormallyaccomplishedusingabendingmachineandthebendradiusinusually5DRorgreater.SeeFigure9.

• MiterBend:Miterbendssometimesoccurinolderpipelineswhenthedirectionchangeisaccomplishedbymitercuttingshortsectionsofpipe,thenweldingthemtogethertochangethepipedirection,asshowninFigure10.Today’spipelineconstructioncodesdonotallowtheuseofmiterbendsinenergyrelatedpipelinesduetothepressurecontainingweakness.

1.5x12=18”Radius

12-inchNominalPipe(304.8mm)(12.750-inchactualO.D.)(323.8mm)

18”R.(457.2mm)

Fig 7. 1.5 DR Bend

3x12=36”Radius

36”R.(914mm)


Fig 8. 3 DR Bend

5x12=60”Radius

60”R.(1254mm)


Fig 9. Field Bend

Min. Spacing

Min. I.D

.

Max. Angle

Max. Angle

Fig 10. Miter Bend

• 7

2.3 Valves

Full-opening/Full-borethroughconduitgatevalvesandballvalvesprovideunobstructedpigpassagethroughtheline.However,ifoldergatevalves,suchasthatshowninFigure11areused,comparetheirseatringspacingwiththemaximumseatringspacingspecifiedforthepig.

Ifcheckvalvesareused,thepigmustbeabletospanthebowllength(seeFigure12).Spheresandshortpigswilloftenstopinthebowlandallowtheproducttobypassaroundtheminthisoversizedarea.

Ifmotorizedautomatedvalvesareusedinstationpiping,electricpigsignalindicators(Figures13-15)canbeconsideredasswitchestoopenandclosevalvesasthepigtraversesthroughthestationmainlinepiping.

2.4 Pig Passage Indicators

Pigpassageindicators,showninFigures13-15,areusedtodetectapigpassingagivenpoint.Theyarecommonlyusedtoshowthatapighasleftalauncherorhasenteredthereceivertrap.

Pigsignalindicatorsarealsousedasswitchestoautomaticallycontrolvalvingatpumporcompressorstationsasthepigpassesthrough.

Fig 11. Seat Ring Spacing

Fig 14. PIG-SIG® V with Electrical and Flag Indicators

Fig 15. PIG-SIG® NIXT Pig Passage Indicator

Fig. 13. PIG-SIG® IV Pig Passage Indicators

Fig 12. Sphere in a Check Valve

• 8

2.5. Tees

Inlineteeswithoutletswhichare50percentorgreaterofmainlinepipesizeshouldhaveguidebarsinstalledacrossthebranch.Thispreventsthepigorcleaningelementfromenteringthebranchoutlet.Thecouponshouldbereplacedinthetappedhole(Figure16)onSTOPPLE®fittings.Ontappingtie-infittingsitisrecommendedaflow-throughplugassemblybeinstalled(Figure17).

Avoidweldingteesadjacenttooneanother.Suchfabricationcancauseapigtostopinthelinebecauseofthelargevolumeofbypassaroundthecups.SeeFigure18.

2.6. Laterals

Figure19illustratesanangledlateral.Comparethelateralbranchlengthtopiglength.Thepigmustbeabletospanthelateralopening.

2.7 Pipe Inside Diameter

Drasticchangesinthepipeinsidediameter(ID)shouldbeavoided.Comparethe(ID)ofthelinetothepigcup’sminimumandmaximumpipelineinsidediameter.LineIDchangesshouldbewithinthesespecifications.

2.8 Dual Diameter Lines

Pipelinescontainingdifferentdiametersofpipeshouldbeavoided.However,thereisaselectionofdual-diametercleaning,batchingandinspectionpigs.Werecommendcarefullyselectingadual-diameterpigforthegivenapplication.

Fig 16. Coupon Attached to Completion Plug

Fig 17. LOCK-O-RING® with Guide Bars

Fig 18. Bypassing at Side Openings Causes Pig Stoppage

Fig 19. Typical Lateral

Coupon(rotatedforclarity

STOPPLE®Fitting

Pipeline

• 9

1.0 Introduction

Theprimarypurposeofapiglauncherandreceiveristolaunchand/orreceiveapipelinepiginto/fromapipelinesystemwithoutinterruptionoftheflow.Pipelinesoperate24houraday,sevendaysaweek,365daysayeardeliveringproducttotheirusers.Operatorscannotaffordtoshutdowntheoperatingsystemjusttopigtheline.Besidesthat,itisproductflowthroughthepipelinethatmovesthepigalong.Therefore,apiggingsystemallowsthepigstobelaunchedandreceivedwithoutflowinterruption.

Piglaunchingandreceivingsystemsvaryfromonetoanotherdependingonspecificpurposeandproduct.Variationsincludeplacementofvalves,lengthoflaunch/receivetube,andtypeofclosuredoor,tonameafew.Inrecentyears,thedesignof“standard”launchersandreceivershaschangedbecauseoffederalregulationsrequiringin-lineinspection,thelengthandweightofin-lineinspectiontools,andresultantsafetyconsiderations.Thus,proceduresforoperatingasystemwillvaryfromonesystemtoanother.Specificlaunchandreceiveproceduresmustbedevelopedforeachsystem.Varioussystemsareshownattheendofthissection.AtypicalpiglaunchsystemisshowninFigure20.

Useofalltheidentifiedvalvesisrequiredtocompleteasafeandsuccessfulpiglaunch.Ifthevalvesarenotopenedorclosedinthepropersequence,damagetopigandpipelinesystemmayoccur.Thereforeaprovenoperatingproceduremustbefollowedineachlaunchoperation.

Pig Launching and Receiving Traps

S e c t i o n I I I

Fig 20. Typical Pig Launching System

• 10

2.0 Launch and Recovery Procedures

Duetothevaryingconfigurations,launchingandreceivingproceduresmustbeestablishedforeachuniquesystemdesign.Thefollowingproceduresaretobeusedasguidelinesforabasicpiggingsystemandmaynotbeappropriateforanygivensystem.

Oneofthemostcriticaloperationsisopeningtheclosuredoor(accesstothetrap).Theoperatormustensurethatthetraphasbeendrainedandthatthereisnopressureinsidebeforeopening.Examplesofclosuresshownbelowhaveapressurewarninglockwhichmustbeopenedpriortoopeningtheclosuredoor.Openingthislockprovidesapositiveindicationofwhetherpressureexistsornot.

ShowninFigure21areathreadedclosureforsmallertrapsandaclampringclosure,whichcanbeusedonthelargestclosure.Onthelargerclampringclosure,ratchetassistsareavailabletohelptheoperatoropentheclamprings,thenopenthedoor.Eachofthesetypeshasapressurewarninglockthatmustbeopenedpriortoopeningthedoor.

Thingstorememberinlaunchingandreceivingapig:

•Neveropenorcloseavalvewithoutknowingthespecificfunctionofthatvalve.

•Openandclosevalvesslowly.

•Whentheclosuredoorisopenduringtheinsertionorremovalofapig,thereisariskofexplosivegas-airmixture.Anyignitionsourceshouldbeeliminated.

•Neverstandinfrontaclosuredoorwhenopeningorclosing.

•Beforeattemptingtoopenaclosuredoor,confirmthatthereisnointernalpressureinthetrap.Makesureventanddrainvalvesarefullyopen.

•Wearappropriatesafetyclothingwhenconductingpiggingoperations.

•Haveappropriatesafetyequipmentavailableincaseofemergency.

•Avoidbreathinghazardousmaterial,andalwaysfollowdescribedproceduresforthedisposalofhazardouswaste.

•Thefollowingaregenericlaunchandrecoveryproceduresfortypicaloperatingsystems.Sincetheproceduresforliquidandgassystemsaredifferent,theyarecoveredseparately.Aliquidlaunchermustbedrainedintoasumptankwhereasagaslauncherisnormallyventedtotheatmosphere.

D-500ThreadedClosure

D-2000ClampRingClosure

Fig 21. Trap Closures

• 11

2.1 Launch Procedures Liquid Service *

RefertoFigure22.Startingcondition:Thetrapispressurizedandfullofliquid.ValvesA,BandCareopen.ValvesD,EandFareclosed.

A.CloseMainlineTrapValveAandTrapKickerValveC.

B.DrainthelaunchingtrapbyopeningDrainValveEandallowairtodisplacetheliquidbyopeningVentValve(s)D.

C. Whenthetrapiscompletelydrainedandvented(zeropsig),withvalvesDstillopen,opentheclosuredoorandinsertthepigsothatthefirstcupformsatightfitinthereduceratpointX.Ifalargeandheavyinlineinspectionpig,itcanbepulledintothetrapbyopeningandusingthepullingnozzles.

D. Closeandsecuretheclosuredoor.CloseDrainValveEandleaveVentValve(s)Dopen.Ifthepullingnozzleswereused,closethesevalvesorreplacetheflanges.SlowlyfillthetrapthroughtheTrapKickerValveCandEqualizationValveF,andventtheairthroughVentValve(s)D.Whenfillingiscompleted,closevalve(s)DtoallowpressuretoequalizethenclosevalveCandF.

E. OpenValveAfirstandthenValveC.Thepigisnowreadyforlaunching.

F. PartiallyclosetheMainlineBypassValveB.ThiswillincreasetheflowofliquidthroughValveCandintothetrapbehindthepig.ContinuetocloseValveBuntilthepigmovesoutofthetrapintothemainlineassignaledbythePIG-SIG®pigpassageindicator.

G.Whenthepigleavesthetrapandentersthemainline,openValveBfully.

mainlinebypassvalve

BF

closure

mainlinetrap valve

equalizationvalve

ventvalve

pullingnozzle

ventvalve

DDpressuregauge

A

Ctrapkickervalve

Edrainvalve

pig signal

�owXFig 22. Launching Procedures, Liquid Pipeline

*Thispublicationisnotintendedtoreplaceproductmanuals.Pleaseseetheappropriateproductmanualsforcompleteinstructions/procedures.

• 12

mainlinebypass

valveB

�ow closure

mainlinetrap valve

ventvalve DD

pressuregauge

ventvalve

A

Creturnlinevalve

E drainvalve

X

pig signal

2.2 Receiving Procedures Liquid Service *

Receivingsystemsareslightlydifferentthanlaunchsystems.Themostnotabledifferencesarelengthofpiping,locationofPIG-SIGIndicatorandbypasspiping.

Asinlaunchingapig,receivingapigshouldfollowadescribedsequencetoavoidsimilarproblems.Therefore,thefollowingproceduresshouldbeutilizedtoreceivepigs.RefertoFigure23.

Starting Condition:Trapisemptyatatmosphericpressure.TheMainlineBypassValveB,DrainValve(s)DandVentValveEareopen.TheMainlineTrapValveA,andtheReturnLineValveCisclosed.Theclosuredoorisclosedandsecure.

A. CloseDrainValveE.SlowlyfillthetrapbyopeningReturnLineValveC,ventingairthroughValve(s)D.

B. Whentrapisfull,closeVentValvesDtoallowtrappressuretoequalizewithlinepressurethroughReturnLineValveC.

C. WithReturnLineValveCopen,openMainlineTrapValveA.Thetrapisnowreadytoreceiveapig.

D. Whenthepigarrives,itmaystopbetweentheteepointXandtheMainlineTrapValveA.

E. PartiallycloseValveB.ThiswillforcethepigintothetrapduetoincreasingflowthroughValvesAandC.

F. WhenthepigisinthetrapassignaledbythePIG-SIGpigpassageindicator,openValveBcompletelyandcloseValvesAandC.

G. OpenDrainValveEandVentValvesDanddrainthetrapofliquidandpressure.

H. Afterthetrapisfullydrained(0psig),withvalvesDandEstillopen,opentheclosuredoorandremovethepig.

I. Closeandsecuretheclosuredoor.

Fig 23. Receiving Procedures, Liquid Pipeline


• 13

2.3 Launch Procedures Gas Service *

RefertoFigure24.Startingcondition:Trapispressurizedandfullofgas.MainlineTrapValveA,Main-lineBypassValveBandTrapKickerValveCareopen.VentValve(s)D,DrainValveEandEqualizationValveFareclosed.

A. CloseMainlineTrapValveAandTrapKickerValveC.

B. OpenVentValve(s)DandDrainValveEtoventtraptoatmosphere.

C. Whenthetrapiscompletelyvented(zeropsig)withVentValvesDstillintheopenposition,opentheclosuredoorandinsertthepigsothefirstcupformsatightfitinthereducer(pointX).Ifalargeandheavyinlineinspectionpig,itcanbepulledintothetrapbyopeningandusingthepullingnozzles.

D. Closeandsecuretheclosuredoor.OpenEqualizationValveFtoallowpermitpressureequalizationinfrontofandbehindthepig.Ifthepullingnozzleswereusedtoloadthepig,closethemorreplaceandsecureblindflanges.PurgeairfromtrapthroughVentValvesDandDrainValveEbyslowlyopeningTrapKickerValveC.Whenpurgeiscompleted,closeVentValvesDandDrainValveEtoallowpressureintraptoequalizewithpipelinepressure.Then,closeValvesCandF.

E. OpenMainlineTrapValveA,thenTrapKickerValveC.Thepigisnowreadyforlaunching.

F. PartiallycloseMainlineBypassValveB.ThiswillincreasegasflowthroughValveCandbehindthepig.ContinuetocloseValveBuntilthepigmovesoutofthetrapassignaledbythePIG-SIGscraperpassageindicator.

G.Whenthepigleavesthetrapandentersthemainline,openMainlineBypassValveBfully.

mainlinebypassvalve

BF

closure

mainlinetrap valve

equalizationvalve

ventvalve

pullingnozzle

ventvalve

DDpressuregauge

A

Ctrapkickervalve

Edrainvalve

pig signal

�owX Fig 24. Launching Procedures, Gas Pipeline


• 14

2.4 Receiving Procedures Gas Service *

Pigreceivesystemsareslightlydifferentthanlaunchsystems.Themostnotabledifferencesarelengthofpiping,locationofPIG-SIGIndicatorandbypasspiping.

Asinlaunchingapig,receivingapigshouldfollowadescribedsequencetoavoidsimilarproblems.Therefore,thefollowingproceduresshouldbeutilizedtoreceivepigs.RefertoFigure25.StartingCondition:Trapisemptyatatmosphericpressure.MainlineBypassValveB,VentValve(s)DandDrainValveEareopen.MainlineTrapValveAandReturnLineValveCareclosed.

A. Topurgeairfromthetrap,closeDrainValveE.SlowlyopenTrapKickerValveC.

B. Afterpurging,allowthetrappressuretoequalizetopipelinepressurebyclosingVentValve(s)D,leavingTrapBypassValveCopen.

C. WithTrapBypassValveCstillopen,openMainlineTrapValveA.Thetrapisnowreadytoreceivethepig.

D. Whenthepigarrives,itmaystopbetweenthetee(pointX)andtheMainlineTrapValveA.

E. PartiallyclosetheMainlineBypassValveB.ThiswillforcethepigintothetrapduetoincreasingflowbehindthepigthroughtheMainlineTrapValveAandReturnLineValveC.

F. Afterthepigisinthetrap,asindicatedbythePIG-SIGpigpassageindicator,openMainlineBypassValveBandcloseMainlineTrapValveAandReturnLineValveC.

G. OpenDrainValveEandVentValvesDtoventthetraptoatmosphericpressure.

H. Afterthetrapisvented(zeropsig)anddrained,withvalvesDandEopen,opentheclosuredoorandremovethepig.

I. Closeandsecuretheclosuredoor.

mainlinebypass

valveB

�ow closure

mainlinetrap valve

ventvalve DD

pressuregauge

ventvalve

A

Creturnlinevalve

E drainvalve

X

pig signal

Fig 25. Receiving Procedures, Gas Pipeline


• 15

3.0 Sample Pigging Systems

Piglauncherandreceiversmaylookthesameinapipingandinstrumentationdiagram(P&ID)orschematicdrawing;however,theymaylooktotallydifferentinthefield.Piggingsystemsaredesignedtofitthespecificsofapipelineandoftentofulfillaspecificpurpose.Thefollowingaresomeexamplesofthevariousconfigurationsusedtolaunch/receivepigs.

3.1 Vertical Launcher

Figure26showsaverticalautomatedsystemthatwillholdthreedisplacementpigs.ThislauncherwasinstalledinawaterfloodsystemontheNorthSlopeofAlaska.Thelaunchercanbeoperatedremotelytolaunchpigsonapre-settimescheduletoremovewaterfrompipingbeforefreezingifthesystemwreretofail.

3.2 Standard Pig Launcher

Figure27showsa“standard”piglauncherifthereisanythingsuchasstandard.Itisdesignedtolaunchonepig.Clearlyshownarethemainlinetrapvalve,mainlinebypassvalveandthetrapkickervalve.

3.3 Dual Launcher

Figure28showsauniquecombinationoftwolaunchers,servingtwopipelines,installedonthesameskid.Thissystemwasdesignedforuseinclosequartersonanoffshoredrillingplatform.

3.4 Automated Batch System

Figure29showsa42-inchautomatedbatchsystem.Fivebatchingpigsareloadedandwillbelaunchedin-dependently.Afterloading,alllaunchesaredonefromaremotelocation.Thefivedevicesontopofthebarrelarelaunchpinsthatholdthepigsinposition.Duringlaunchoperations,thevalvesaresequencedandalaunchpinretracted,launchingapig.Pigpassageindicatorsconfirmthelaunch.

Fig 26. Vertical Launcher

Fig 27. Standard Pig Launcher

Fig 28. Dual Launcher

Fig 29. Automated Batch System

• 16

3.5 Sloped Launcher

AsopposedtotheverticallaunchershowninFigure26,thelaunchershowninFigure30isconstructedonaslope.Itholdsfourpigsandisdesignedtolaunchpigsthatwillbatchmultipleproducts.Thepigsarecontrolledbytwolaunchpinsontopofthetrap.Exceptforloading,thetrap,whichhastwotrapkickerlines,isonlineallofthetime.Tolaunchapig,alaunchpinisretractedandthepigslidesdownintotheline.

UNISPHERE™launcherscanbeconstructedinasimilarmanner,withlaunchpinscontrollingthelaunchofasmanyastwelvespheres.AdiagramofoneisshowninFigure31.

3.6 Combo Pig/Sphere Launcher

Whenitisnecessarytorunmultiplespherestoremoveliquidsbutretaintheoptiontorunacleaningpigorinspectiontool,acombinationpig/spherelauncherisdesirable.

3.7 Inline Inspection Pig Launcher

Aninlineinspectionpiglauncherissimilartothestandardlauncherexceptthatithasamuchlongerbarreltoaccommodatethelongerinlineinspectiontools.Clearlyshownarethemainlinetrapvalve,mainlineby-passvalveandthetrapkickervalve.Thereducer,thepointatwhichthebarrelsizereducestopipelinesize,canbeseen.Accessflanges(pullingnozzles)shownonthelinesizepipeprovideaccesstothetrapforpullinganinspectiontoolintothetrap.ThispullingnozzleconfigurationisshownonthediagraminFigure24.

Fig 30. Sloped Launcher

Fig 31. Combo Pig/Sphere Launcher

Fig 32. Inline Inspection Pig Launcher

• 17

1.0 Introduction

Pigsareavailableinavarietyofcombinationstoperformvariousfunctionsinapipeline.Figure33showsanalmostendlesscombinationofpigsthatperformavarietyoffunctionsinseveraldifferenttypesoflines.

Pigsaredesignedtoperformaspecificfunction.Toselectaproperpigconfiguration,theoperatormustknowthefollowingthings:

• PipelineSize

• WallThickness(es):

• MinimumBendRadius(radius&degreeofbend)

• PipelineLength

• ProductMedia(gas,oil,etc.)

• FlowRate/Velocity:

• SideConnections(teesbarred/unbarred)

• ValveType(Valvesshouldbefullbore/fullopening.Valveshaveinternalcavity)

• PiggingApplication

• PiggingHistory

1.1 Pig Components

Pigscanbeconfiguredwithdifferentcomponentstoperformspecificfunctions.Thefollowingisalistofthesecomponentsandtheirfunctions.

A. Brushes:Brushesareusedprimarilyforremovinghardinternaldepositssuchasscaleandcorrosionoffpipewalls.Somebrushesarewear-compensating.Anothertypeofbrushisusedtoremovedepositsfrompitstoallowcorrosioninhibitorsandbiocidestodetercorrosioninthepipeline.

B. Cups:Cupsprovidethesealofthepiginsidethepipelineandpermittheflowinthepipelinetomovethepigalong.Theyalsoprovidesomecleaningofthepipewall.Theyarealsousedforbatchingproducts.

C. Discs:Discsareusedtoenhancecleaningandprovidesupporttothepigwhileinthepipeline.Apigequippedwithdiscsmayrunbidirectionally.

D. Blades:Bladesareusedtoremovesoftdepositssuchasparaffinandsludgethatformonthewallsincrudeoillines.

Fig 33. Variety of Pigs

Selecting the Right Pipeline Pig

S e c t i o n IV

• 18

E. Magnets:Magnetsareusedtoremoveferrousmetalslikemetalchips,usedweldingrodsandironoxidescontainedinblackpowder.Magnetsarealsousedtotripnon-intrusivepigpassageindicators.

F. FoamPigs:Foampigsarenormallyusedindryingpipelinesfollowinghydrostatictesting.

1.2 Reasons for Pigging

A. Construction

1.Removingconstructiondebrisfromtheline.

2.Hydro-test(waterfilling,dewatering).

3.Gauging.

B.Operation

1.Commissioning.

2.Cleaning.

3.Condensate/waterremoval.

4.Productseparation(batching).

5.Applicationofinhibitors.

C.Inspection

1.Tocheckforphysicaldamage(geometry).

2.Todetectmilldefects,corrosion,laminationsorcracking.

D.MaintenanceandRepair

1.Pre-inspectioncleaning.

2.Isolation.

E.Renovation/Rehabilitation.

1.Chemical/gelpigging.

2.Scaleremoval.

3.Cleaningforproductconversion.

4.Decommissioning.

5.Recommissioning.

2.0 Pig Selection

Thefollowingaregeneralguidelinestoapplywhenselectingapig.Completingapigapplicationform,asampleofwhichiscontainedinAppendixI,andprovidingittoyoursupplierwillassisttheminrecommendingapig.

2.1 Cleaning a Line (New Construction, Refined Products, Natural Gas or Crude Oil)

A.Thebestchoiceofapigisonewithdiscs,conicalcups,spring

Fig 34. Pig with Brushes, Cups and Discs

Fig 37. Pig with Spring Mounted Brushes

Fig 38. Pig with Urethane Blades

Fig 35. Pig with Discs Only

Fig 36. Pig with Cups Only

• 19

mountedbrushesorurethaneblades,andbypassports,asshowninFigure34.

B.Discs(Figure35)areeffectiveatpushingoutsolidswhilealsoprovidinggoodsupportforthepig.

C.Conicalcups,showninFigure36,provideexcellentsealingcharacteristics,areabletotraversesignificantreductionsandwearwell.

D.Springmountedbrushes(Figure37)arewear-compensatingandprovidecontinuousforcefulscrapingforremovalofrust,scaleandotherbuildupsonthepipewall.

E.Whencleaningwaxycrudeoilfromthewallsofcrudeoillines,urethanescraperblades,showninFigure38,areoftenpreferredbecausetheyareeasiertocleanthanbrushes.

F.Bypassportsallowsomeofthepipelineproducttoflowthroughthepig,asshowninFigure39.Thishelpsminimizesolidsbuild-upinfrontofthepig.Bypassmayalsoreducethespeedofthepigthroughthepipeline.

G.Whencleaningnewconstruction,pigswithmagneticcleaningassemblies,showninFigure40,arerecommendedforremovingferrousmetaldebrissuchasweldingrods,nutsandbolts,andtools.

2.2 Displacement Applications

Displacementapplicationsincludefillinganddewatering,commissioninganddecommissioningapplications,nitrogenpurging/inertingandbatchingproductsinrefinedproductlines.

Thebestchoicewouldbeafourcuppigwithmulti-lippedconicalcups.

A. Conicalcupswillmaintaincontactwiththepipewall,eveninout-of-roundpipe.Asthepipesizeincreases,theout-of-roundnessconditionbecomesmorecommon.Conventionalcupsanddiscscannotmaintainasealinout-of-roundordentedpipe.

B. Multi-lippedcupshavenumerousindependentsealinglipsoneachcup,suchasthoseshowninFigure41,whichgreatlyimprovesitsabilitytomaintainaseal.

Otheralternativesinclude:

A. FoamPigs.Somefoampigsprovidearelativelygoodsealovershorttomoderatedistances.Thecostsarelowandthereislittleriskofgettingstuck.Lowdensityfoampigsarecommonlyusedinlargenumbersfordryingpurposesafterinitialwaterremoval.

B. Bidirectionaldiscpigsaretypicallyusedinfillinganddewateringoperationsassociatedwithhydrostatictestingwhenthewaterusedtofillthelinehasto

Fig 39. Flow Through Bypass Pushes Debris Ahead of Pig

Fig 40. Pig with Magnets to Collect Debris

Fig 42. Foam Pigs

Fig 43. 6-Disc Bidirectional Pig

Fig 41. Multi-lipped Cup

• 20

bepushedbacktoitssourceaftercompletionofthetest.Ifitispossibletoreverseflow,thispigcanbereturnedtoitslaunchpointifthereisafearofthepiggettingstuck.

2.3 Removing Liquids from Wet Gas Lines

A. UNISPHERE™pigs(Figure44)arethepreferredchoiceforremovingliquidsfromgaslines.

B. Spherepiggingsystemsareusuallydesignedtoautomaticallylaunchandreceivespheres.Anumberofspherescanbeloadedintotheautomaticlauncherandarelaunchedatpredeterminedfrequencies.

C. Atthereceivingendoftheline,aslugcatcherisinstalledtocapturetheliquidpushedinbythesphere.Spheresarelaunchedatafrequencythatpreventsexceedingthecapacityoftheslugcatcher.

D. Atthereceivingend,spheresarecapturedinareceivingtrap.Pigpassageindicatorsareinstalledonthelaunchersandreceiverstocountthespherelaunchesandrecoveries.Alaunchermayalsobeequippedwithverticallaunchpinsthatwillextendandretract,cyclingthelaunchingofspheres.

E. Pipelinesystemsarenormallydesignedfortheuseofspheresorpigs,butnotboth.Systemsdesignedforlaunchingandrecoveryofspheresmayrequiremodificationoflaunchersandreceiversbeforeconventionalpigscanbeused.

2.4 Removal of Ferrous Debris

Debrissuchasweldingrods,bolts,tools,etc.,leftafterpipelineconstruction,mustberemovedbeforeattemptingtoruncorrosioninspectionorothertypesofinspectionpigs.Itisverydifficulttoremovethisdebriswithconventionalpigs.Conventionalpigswillpushtheseobjectsforadistancethenrideoverthem.Themosteffectivewaytoremovethisdebrisisattachingamagneticcleaningassemblytoaconventionalpig.Amagneticcleaningassemblynormallyconsistsofamagneticbeltthatwrapsaroundthebodyofapig.Figure45showstheferrousdebristhatcanbepickedupbymagnetsattachedtothepig.

2.5 Removal of Hard Scale Deposits

Cleaninghard,largedepositsisaspecialapplicationthatwouldnormallybeprovidedbyapipelinecleaningservicecompany.Aggressivepigscombinedwithcleaningfluidsarerequiredforthisapplication.Referredtoaschemicalcleaning,theyareoftenusedwithcleaningdetergentfluidsthathelptoattackthedepositsandkeeptheremoveddebrisinsuspensionwhilebeingpushedoutoftheline.Thispermitsremovaloflargevolumesofsolidsinonepigrun.

Fig 44. UNISPHERE™ Pigs

Fig 46. Portable Separator - to Remove Liquids and Debris from Natural Gas Pipelines

Fig 45. Pig with Magnets to Collect Debris

• 21

A. Thecleaningfluidsarecapturedbetweenbatchingandcleaningpigs.Normally,aslugofthefluidisintroducedinfrontofthefirstpig.

B. Samplesofthedepositsmayberequiredforchemicalanalysisandtodeterminethebesttypeofcleaningfluids.

2.6 Applying Corrosion Inhibitors

Corrosioninhibitorsarenormallyinjectedintothelineonacontinuousbasisandcarriedthroughthelinewiththeproductflow.Often,inhibitorsarebatchedbetweentwopigs.Sincethemajorityoftheflowisinthebottomhalfofthepipe,thereislittleassurancethatthetopwallofthepipe(12o’clockposition)istreatedbytheinhibitor.

Specialpigshavebeendevelopedthatsprayinhibitortothetopofthepipeastheytravelthroughthepipeline,asshowninFigure47.Thisisdonebyusingasiphoningeffectcreatedbybypassflowthroughanorificespecificallydesignedtopickupinhibitorfromthebottomofthepipe.

2.7 Pre-Inspection Cleaning

Priortoconductinganinlinecorrosioninspectionsurvey,thepipelinemustbeclean.Thecleanertheline,themoreaccuratethesurveydata.

Linescarryingrefinedproductsrequireverylittlecleaningwhileacrudeoillinemayrequireextensivecleaning.Dozensofindividualpigruns,oroneormoretrainpigs(twoorthreepigscoupledtogetherwithflexibleconnectors)mayberequired.Trainpigsnormallyhavemultiplediscs,cups,extrabrushesandmagneticcleaningassemblies.

Chemicalcleaning,describedinparagraph2.5,mayberequiredonlonglinescontainingexcessiveparaffin,ironoxideorothersolids.

2.8 Cleaning Lines with Known Internal Corrosion

Specialpigsavailableforthisapplicationhaveindependentscrapingwiresthatwillgointoapittobreakupandremovedeposits.Suchdeposits,ifleft,wouldpreventcorrosioninhibitorsfromgettingintothecorrosionarea.SuchapigisshowninFigure48.Brushesonconventionalpigswillnotextendintopitsintheline.

Fig 47. Corrosion Inhibitor Distributed to Top of the Pipe

Fig 48. PitBoss™ Pigs

• 22

2.9 Cleaning Internally Coated Lines

Thepreferredchoiceforthisapplicationisapigwithdiscsandcups.Becauseofthecharacteristicsofepoxycoatings,discsandcupswillnormallyremovedepositswithoutharmingthecoating.

Conventionalcleaningpigswith“prostran”brushesorpolyurethanebladesisanotheroptionforcleaninginternallycoatedpipe.

2.10 Pigging Offshore Pipelines

Offshorepipelinesusuallyrequirespeciallydesignedpigsinordertoaccommodate:

A. Veryheavywallpipe.

B. Largevariationsinwallthicknessesduetodifferentdesigncodesforplatformandriserpipingversussubseamainlinepipe.

C. Lateralsandwyefittingsareoftenusedwhichrequireextralongpigs.

Effectivepigscanbeprovidedforthesesystemsbutmayrequirespecialdesignfeatures.

Fig 49. Urethane Blades and Plow

• 23

1.0 Introduction

Pigginganewconstructionline,beforeitisplacedinservice,isdoneforanumberofreasons.Firstofall,theoperatorwantstoremoveconstructiondebrisleftinthepipe.Thelinemustbefilledwithwaterandhydrostaticallytested.Oncehydro-testingiscompleted,thewatermustberemoved.ThelinethenmustbeinspectedusingaGeometryInspectionTooltoassurethelineisfreeofdentsorbuckles.Thelinemustbefurthercleanedanddriednormallytoadewpointspecification(-20ºFto40ºF).

• Ifthepurposeofpiggingistoensurethatthelinehasafullroundopeningfromoneendtotheother,agaugingpigcanbeused.Thegaugingpigwillalsoremovemostconstructiondebrissuchasskidsandweldingrods.

• Ifthepurposeistocleanrust,dirt,ormillscale,astandardcleaningpigcanbeutilized.

• Ifthepurposeofpiggingistofillwithhydrostatictestwater,adisplacementpigisused.

2.0 Selecting the Pig

2.1 Gauging Pigs

A. TheKALIPER®360Surveydevice,showninFigure50,isaself-contained,instrumentedtoolwhichrecordssizeandlocationofpipediameterreductions.Itcandetectdents,buckles,flatspotsandconstructiondebris.TheKALIPER360toolcanalsodetectachangeinpipewallthickness.Additionally,theKALIPER360toolwillprovideinformationontheo-clockpositioningoftheanomaly.

B. Aconventionalgaugingpig,showninFigure51,isequippedwithaslottedaluminum“gaugingflange”.Thisgaugeplatepigwillprovidelimitedinformationonminimumborewithinagivensectionofpipe.

2.2. Cleaning Pigs

TDWcleaningpigsmayemploymagnetsforremovalofferrousmetals,discsandcleaningelements,includingbrushesorurethaneblades.Brushescanbeusedinnewlineconstructiontoremovemillscaleorconstructiondebris.Figure52isanexampleofapigwithwear-compensatingbrushes.

2.3. Displacement Pigs

Displacementpigsarealsousedfordisplacingairandhydrostaticwaterpriortocommissioninganewpipeline.Theycanbeusedbidirectionally(runinbothdirections).

Fig 52. Cleaning Pig with Wear-Compensating Brushes

Fig 51. Conventional Gauging Pig

Fig 50. KALIPER® 360 Inspection Tool

Pigging New Construction

S e c t i o n V

• 24

A. Abidirectionalpig,showninFigure53,iseffectivefordisplacingairorhydrostatictestwater.Thebidirectionalpigmaybeleftinthelinewhilethetestisbeingconducted,thenreversedforwaterremovalifdesired.

B. Theurethanediscisaneffectivecleaningelement,providespigsupportandcanrunbidirectionally.

C. TheOptionAll™BatchingPig,showninFigure54,canbeusedtodisplaceairorhydrostatictestwater.Itisfittedwithpolyurethaneconicalcupsthatpermitthepigtopassoverobstructionsinthelinewithoutpigdamage.Conicalcupsconformtoout-of-roundpipe,providingacontinuousseal.

D. TheInflatableUNISPHERE™,showninFigure55,isaseamless,liquidcastpolyurethaneball.Itwilltraverseshortradiusbendswherethebodytypepigwillnot.UNISPHEREPigsareidealforremovingliquidsfromnaturalgaslineswherefrequentrunsarerequired.Automatedspherelaunchersandreceiversarenormallyusedintheseapplications.TheycanbesizedtomatchmostpipeIDs,rangingfromstandardwalltoultra-thinwallpipe.

UNISPHEREPigsarefilledcompletelywithliquid(usuallyglycoland/orwater).Theinflatingvalveisremovedandliquidispoureddirectlyintothesphere.Thevalveisreplacedandthesphereissizedbypumpinginadditionalliquid.

3.0 Propelling the Pig

3.1 Speed

Themosteffectivespeedforpiggingduringconstructionisconsideredtobe1to5miles(1.60to8km)perhour.Pigvelocitiesmuchgreaterwillcausethepigstobecomelesseffective.

3.2 Propelling the Pig with Air

Manytimesagaugingorcleaningpigispushedwithairthroughshorttestsectionsofpipe.Itisrecommendedthatthelinebeprepackedwith50-100psiandcarefullycontrolledasthepigsarepropelledthroughtheline.

WARNING: High speed runs through bends can cause damage to the pipeline, the pig, or both.

Fig 55. Inflatable UNISPHERE™ Pigs

Fig 54. OptionAll™ Batching Pig

Fig 53. 6-Disc Bidirectional Pig

• 25

Table1listsvariouspipesizes,recommendedcubicfeetperminute(CFM)andmeterscubedperhour(m3/h),atatmosphericconditions.

Table 1. Compressed Air Required vs. Pipe Size

PipeSize(in.) mm CFM@150psi M3/h

6 200 100 170

12 300 300 510

18 450 700 1,190

24 600 1,200 2,040

30 750 1,900 3,230

36 900 2,800 4,750

42 1,050 3,800 6,450

48 1,200 5,000 8,500

A. Pigsoftenrequiremorepressuretostartmovement.Dependinguponpiggingapplication,compressorsshouldbeabletodeliverthedesiredCFMat150psi.

B. Thepigwillstalliftheairoutputvolumeisnotlargeenoughtofillthelineatauniformrateandpressure.Ifthepigstops,pressurewillbuilduntilthepressurereachesasufficientlevel,thenthepigwillbepropelledatahighrateofspeedandwillcontinueatthisrateuntiltheflowandpressureisinsufficienttokeepitmovingconsistently.Thisiswhyitisimportanttohavesufficientflow,pressureandexperienceinconductingthisoperation.

3.3 Propelling the Pig with Water

A. Waterisoneofthemorecommonfluidsusedtopropelpigsthroughanewline.

B. Whenahydrostatictestisconducted,apigisplacedaheadofthewatertoremoveairfromtheline.Itiscriticaltoachieveacompletelinefill,allowingnoairinthehydrostaticwaterlinefill.

C. Theprincipalconsiderationforfillingthelineis:

1.Wateravailabilityandfillrate.Itisrecommendedtosizefillpumpsthatwillfillthelineatarateof1mphorgreater.

2.Fillpumpsareconsideredhighvolume-lowpressurepumps.

• 26

D. Table2listspumprecommendationsfordifferentsizepipe.Theflowratesshowninthetablewillpropelthepigataspeedofapproximatelyonemile(1.6km)perhour.Thefollowingformulamaybeusedtodeterminethespeedofthepig.

S=,where:

S=speed,milesperhour

GPM=gallonsperminute

d=Insidediameterofpipe,ininches

TABLE 2. Pump Recommendations vs. Pipe Size

PipeSize(in.) mm GallonsPerMinute(GPM) LitersPerMinute(LPM)

6 200 150 570

12 300 500 1,900

18 450 1,000 3,800

24 600 2,000 7,600

30 750 3,000 1,400

36 900 4,500 17,000

42 1,050 6,000 22,700

48 1,200 8,000 30,300

E. Hydrostatictestpumpsareconsideredlowvolume-highpressure.Atestpumpmusthavetheabilitytoincreasethelinepressuretothetestpressure.Ahighpressurepumpratedat95gallonsperminute(gpm)at5,000psi(360litersperminute,LPM,at345bar)shouldbesuitableforthepressurizingoperation.

Positionofwaterdisplacementpigorpigs

Inletforgastopushpigsoutofheads

Inletforeitherwaterorgas

Rearpositionofairdisplacementpig

Blow-Off Blow-Off

Fig 56. Launching Test Header for Filling Two Test Stations

Positionofwaterdisplacementpig

Positionofwaterandairdisplacementpigsat

completionofwatertransfer

ReceivingHeadLaunchingHead

Rearpositionofairdisplacementbeforewatertransfer


Blow-Off

Blow-Off

Fig 57. Launching and Receiving Test Header for Water Transfer from One Section to Another

.278

d2

• 27

Positionofwaterdisplacementpigorpigs


Inletforeitherwaterorgas


Fig 58. Launching Test Header Equipped for Filling of One Test Section Only

Gasinlet

Waterfillinlet

Waterfillanddraintaps

Inletforgastopushpigoutofhead

PositionofNo.3waterremovalpig




Fig 59. Multiple Pig Launching Test Header

F. Oncompletionofthepressuretest,thewatercanbedisplacedbypushingthedisplacementpigwithair.Pigspeedshouldberegulatedbycontrollingtheflowofwateroutofthedischargeendofthesection.

3.4 Launching and Receiving Test Headers and Traps

A. Pigscanbelaunchedinnewpipelinesbyprovidingaheader/trapontheupstreamendoftheline.Theheader/trapwillallowthepushingfluidtoenterbehindthepig.

B. Areceivingheader/trapisnecessaryonthedownstreamendoftheline.Thereceivingheader/trapwillallowthefluidtoexitaheadofthepig.

C. Figures56,57,58and59arefourgeneraltypesofdesignforlaunchingandreceivingtestheaders.Figure56isforfillingtwosectionsinoppositedirections.Figure57transferswaterfromonesectionthathasbeentestedintoanothersectiontobetested.FillingatoneendofasectiononlyisshowninFigure58.AsetupforrunningseveralpigsisshowninFigure59.Thesetestheadersmaybeandoftenarereplacedwithtemporarypigtrapswithvalvesthatallowformultiplepigruns:cleaning,fill,dewatering,inspectionanddrying.

• 28

• 29

1.0 Introduction

1.1 Raw Gas (Gathering Systems)

Rawnaturalgastypicallyconsistsofmethanecontainingvaryingamountsofthefollowing:

A. Heaviergaseoushydrocarbonssuchasethane,propane,normalbutane,isobutaneandpentanes

B. Watervaporandliquidwater

C. Liquidhydrocarbons.

D. Acidgasessuchascarbondioxide,hydrogensulfide,andmercaptanssuchasmethanethiolandethanethiol.

Producedgasfromthewellheadistransportedtoprocessingplantsthroughanetworkofgatheringpipelines,whichareusuallysmall-diameterlines.Acomplexgatheringsystemcanconsistofthousandsofmilesofpipes,interconnectingmorethan1000wells.

1.2 Processed Gas (Transmission Systems)

Processedgasisthatgaswhichistransportedviatransmissionlinesfromtheprocessingplanttotheutilityandpowercompanies.

1.3 Refined Products

Refinedpetroleumproductsarederivedfromcrudeoilsthroughprocessessuchascatalyticcrackingandfractionaldistillation.Severalexamplesofrefinedpetroleumproductsandtheirpropertiesinclude:

A. Gasoline:Alightweightmaterialthatflowseasily,andmayevaporatecompletelyinafewhours.

B. Kerosene/JetFuel:Alightweightmaterialthatflowseasilyandevaporatesquickly.

C. No.2FuelOil:Alightweightmaterialthatflowseasilyandiseasilydispersed.

D. No.4FuelOil:Amedium-weightmaterialthatflowseasily,andiseasilydispersediftreatedpromptly.

E. LubricatingOil:Amediumweightmaterialthatflowseasilyandiseasilydispersediftreatedpromptly.

F. No.5andNo.6fueloil,BunkerBandBunkerC,arealsorefinedproducts,butareincludedinSectionVII.

Onstream Pigging Natural Gas Lines, Natural Gas Liquids and Refined Petroleum Products

S e c t i o n VI

• 30


Ifthepurposeofpiggingistoremoveinternalbuild-uponthepipewallwhichmayshieldcorrodingareas,acleaningpigshouldbeutilized.

Ifthepurposeofpiggingistoremovecorrosiveorheavyliquids,adisplacementpigorspherecanbeutilized.

Ifmorethanonetypeofproductistransportedthroughapipeline,batchingpigscanbeusedtoseparatetheproducts.

2.1 Cleaning Pigs

TDWcleaningpigsemployfourtypesofcleaningelements:brushes,urethaneblades,discsandmagnets.

A. Brushescanbeusedifthelinecontainsmillscaleorharddepositsadheringtothepipewall.Figure60isanexampleofapigwithsteelwirebrushes.

B. Urethanebladescanbeusedtoremovesoft,sludgedeposits.Figure61isanexampleofapigwithurethaneblades.

C. Bypassportsareincorporatedintomostcleaningpigs.Byopeningtheby-passplug(s),partoftheflowisdivertedthroughoraroundthepigbodytocreateturbulenceaheadofthepig.Thishelpstokeepforeignmattersuspendedinfrontofthepiginsteadofallowingthedirttoaccumulateinandaroundthecupsandcleaningelements.Figure62showsdebrissuspendedinfrontofthepig.

2.2. Batching/Displacement Pigs

A. TDWbatching/displacementpigsemploymultiplecupsordiscsthatmaintainasealthroughbendsandfull-diameterbranchopenings.

B. TheVANTAGE®VPig,showninFigure63,isfittedwithconicalcupsthatpermitthepigtopassoverobstructionsinthelinewithoutpigdamage.Conicalcupsconformtoout-of-roundpipe,providingacontinuousseal.

C. TheInflatableUNISPHERE™Pig,showninFigure64,isaseamless,liquidcastpolyurethaneball.Itwilltraverseashortradiusbendwhereabodytypepigwillnot.TheycanbesizedtomatchanysizepipeIDrangingfromstan-dardwalltoultrathinwallpipe.Twoinflatingvalvesareincorporatedforuseinsystemsthatdonothaveoversizebarrelsforsphereinsertionorremoval.

UNISPHEREPigsarefilledcompletelywithliquid(usuallyglycoland/orwater).Oneinflatingvalveisremovedandliquidispoureddirectlyintothesphere.Thevalveisreplacedandtheballissizedbypumpinginadditionalliquid.Anyhandpumpcapableofpumpingfluidat250psi(17bar)canbeused.

Fig 64. Inflatable UNISPHERE™ Pigs

Fig 60. VANTAGE® Plus Pig with Brushes

Fig 61. VANTAGE® Plus Pig with Blades

Fig 63. Batching Pig

Fig 62. Debris Suspended in Front of the Pig

• 31

1447QPb

P(Fpv)2d2

3.0 Pigging Speed

Normally,pigsarerun“onstream”withthespeedbeingthesameasthestreamvelocity.However,themostefficientspeedsforbodytypepigsare3-7mph(4.8-11.2kmperhour).

Thespeedofcleaningpigscanbevariedslightlybyopeningthebypassport(s).

Howfastdoesgasmoveinapipeline?Thefollowingformulaprovidesacloseapproximationofthespeedofgas.

S=,where

S=Speed,milesperhour

Pb=Absolutebasepressure(barometric)(pressureatcompressor)

P=Absolutelinepressure,

Fpv=SupercompressibilityFactor(SeeTable3)

d=Insidediameterofpipeininches

Table 3. Super-Compressibility Factors Fpv Base Data – 0.6 Specific Gravity Hydrocarbon Gas

Pressure 20ºF(-7ºC) 60ºF(16ºC) 100ºF(38ºC)

psig bar Fpv Fpv2 Fpv Fpv2 Fpv Fpv2

200 13.8 1.0212 1.0428 1.0160 1.0323 1.0123 1.0248

400 27.6 1.0442 1.0904 1.0327 1.0665 1.0247 1.0500

600 41.4 1.0690 1.1428 1.0499 1.1023 1.0370 1.0754

800 55.2 1.0955 1.2001 1.0674 1.1393 1.0492 1.1008

1000 69.0 1.1231 1.2614 1.0847 1.1766 1.0609 1.1255

1200 82.7 1.1506 1.3239 1.1013 1.2129 1.0719 1.1490

1400 96.5 1.1764 1.3839 1.1166 1.2468 1.0818 1.1703

1600 110.0 1.1978 1.4347 1.1298 1.2764 1.0904 1.1890

1800 124.0 1.2126 1.4704 1.1400 1.2996 1.0974 1.2043

2000 138.0 1.2202 1.4889 1.1470 1.3156 1.1026 1.2157

• 32

4.0 Frequency

Thefrequencyofpigrunsandthenumberofpigstoberunwilldependontheconditionsexistingintheline.Eachsectionofasystemcanhavedifferentrequirements,dependingonvaryingaccumulationsofdirt,ironoxide,liquids,etc.

Thesectionsclosesttoproductionoftenhavecondensatesaswellassomedirtthatwasnotremovedatthedehydratingplant.Allsectionsmayhaveaccumulationsofcompressoroilfromtimetotime.Periodicefficiencytestsshouldbemadeoneachsectiontodeterminepiggingschedule.Thecostofrunningapigcanbecomparedtotheefficiencydrop(andassociatedlossinthroughput)todeterminetheeconomicsofpigging.

5.0 Performance

Apig’sperformancecanbedeterminedbyseveralmethods:

A. Measurableincreaseinlineefficiency.

B. Measurableincreaseinthroughput.

C. Pressuredrop.

D. Dewpointdifferentialbeforeandafterpigging.

E. Amountofforeignmatterinthepigreceiver.

F. Amountofliquidsinareservoirbarrel.

G. Reducedcorrosion.

• 33

1.0 Introduction

Crudeoilisthetermforunprocessed,orunrefinedoil,asitcomesoutofthewell.Itvariesincolorandinviscosity.Itcontainshundredsofdifferenthydrocar-bons,basicsedimentsandwaterthathavetobeseparatedbyrefiningintodiffer-enttypesofhydrocarbonstoproduceproductssuchasgasoline,plastics,etc.

1.1 Light Crude

Lightcrudeoilisalowviscositycrudeoil,normallywithalow-waxcontent.

1.2 Heavy Crude

Heavycrudeisanytypeofcrudeoilwhichdoesnotfloweasily.Itpresentsspecialchallengeswithregardtotransportingbyapipeline.Bitumen,fromthetarsandsinCanada,isconsideredtobeextraheavycrudeasitdoesnotflowatallinambientconditions.Tofacilitateflow,extra-lightformsofoilorliquidnaturalgasareaddedatregulardistancesinpipelines.

1.3 Waxy Crude Oils

Wheneverawaxyoilcomesincontactwithacoldpipewall,solidparaffincrystalscanprecipitateanddepositonthepipewallsurface.Eventually,thismaysignificantlyreduceorevenblocktheareaopentoflow.

A. Waxycrudesarewidespreadintheworld.Themajorproblemsrelatedtothetransportationofthiscrudethroughpipelinesisnotjustcrystallizationoftheirwaxcontentatlowtemperatures,buttheformationofdepositswhichdonotdisappearuponheating.Theywillnotbecompletelyremovedbypigging.

B. Waxycrudesarenotcleanand,inadditiontowax,theycontainotherorganicssuchasasphalteneandresin.Theseotherheavyorganicsdonotgenerallycrystallizeuponcoolingand,forthemostpart,theymaynothavedefinitefreezingpoints.Asaresult,applicationofchemicalanti-foulantsandfrequentpiggingbecomenecessary.

C. Severalmethodshavebeenusedtoremoveparaffindeposits,includingmechanicallyscrapingthepipewalls(pigging),contactingtheparaffindepositswithvariousorganicsolventsystemsandtheapplicationofhotoilsorexternalheat.RefertoSectionIVforinformationoncleaningpigs.Figure65showscleaningpigsafterarunthroughacrudepipelinewithparaffindeposits.

Onstream Pigging Crude Oil Lines

S e c t i o n VII

Fig 65. Cleaning Pigs Packed with Paraffin

• 34

1.4 Sour Crude

Sourcrudeiscrudeoilcontainingsulfur.Whenthetotalsulfurlevelintheoilsisgreaterthan0.5percent,theoiliscalled“sour.”Itisgenerallylowinparaffin,andnotwaxy.

A. Impuritiesneedtoberemovedbeforethislowerqualitycrudecanberefinedintogasolineanddieselfuel.Thisresultsinhigherpricedfuelsthanthosemadefromsweetcrude.

B. Sourcrudecanbetoxicandcorrosive,especiallywhentheoilcontainshighlevelsofhydrogensulfide.Atlowconcentrations,theoilhasthesmellofrotteneggs,butathighconcentrations,theinhalationofhydrogensulfideisinstantlyfatal.

C. Athighlevelsofhydrogensulfideandpressure,somesteelswillfailduetosulfidestresscracking.Whentheseconditionsexist,normalspringsteelsandbrushbristleswillbreakunderverylittleload.Alternativematerialsarerequiredforsprings,andstainlesssteelwiresforbrushes.Moststructuralsteelsusedforpigbodiesarenotaffectedbytheseconditions.

1.5 Refined Products

Somerefinedproducts,becauseoftheirweightanddensity,areincludedinthissectionalso:

• No.5FuelOil(BunkerB):Amedium-weighttoheavyweightmaterial.Preheatingmaybenecessaryincoldclimates,andthisfueloilisdifficultifnotimpossibletodisperse.

• No.6FuelOil(BunkerC):Aheavyweightmaterialthatisdifficulttopumpandrequirespreheatingforuse.Thisfueloilmaybeheavierthanwater,isnotlikelytodissolve,isdifficultorimpossibletodisperse,andislikelytoformtarballs,lumpsandemulsions.


Ifthepurposeofpiggingistoremoveforeignmatterandparaffindepositsorscalewhichmayshieldcorrodingareas,acleaningpigcanbeutilized.

Ifthepurposeofpiggingistoseparateproductsorremoveunwantedliquidsandcorrosionproducts,abatching/displacementpigcanbeutilized.

RefertoSectionIVforselectionoftheproperpigtodothejob.

Bypassportsareincorporatedintomostcleaningpigs.Byopeningthebypassplug(s),partoftheflowisdivertedthroughoraroundthepigbodytocreateturbulenceaheadofthepig.Thishelpstokeepforeignmattersuspendedinfrontofthepiginsteadofallowingthedirttoaccumulateinandaroundthecupsandcleaningelements.

• 35

3.0 Pigging Speed

Normally,pigsarerun“onstream”withthespeedbeingthesameasspeedofflowthroughthepipeline.However,themostefficientspeedsforbodytypepigsare3-7mph(4.8to11.3kmperhr.).Flowcanbedeterminedusingthefollowingformula.AppendixIIIcontainshelpfulconversionfactors.

S=,where

S=Speed,MPH

Q=Throughput,bpd

d=Insidediameterofpipeininches

Thespeedofcleaningpigscanbevariedslightlybyopeningthebypassport(s).

4.0. Frequency

Thefrequencyofpigruns,andthenumberofpigstoberun,willdependontheconditionsexistingintheline.Eachsectionofasystemcanhavedifferentrequirements,dependingonvaryingaccumulationsofdirt,paraffin,liquids,etc.

Periodicefficiencytestsshouldbemadeoneachsectiontodeterminepiggingschedule.

Thecostofrunningapigcanbecomparedtotheefficiencydrop(andassociatedlossinthroughput)todeterminetheeconomicsofpigging.

0.0081xQ

d2

• 36

5.0. Performance

5.1 Cleaning Pig Performance

Acleaningpig’sperformancecanbedeterminedbyseveralmethods:

A. Measurableincreaseinlineefficiency.

B. Measurableincreaseinpumpefficiency.

C. Measurableincreaseinthroughput.

D. Pressuredrop.

E. Amountofforeignmatterinthepigreceiver.

F. Milliporetest.

G. Reducedcorrosion.

5.2 Batching Pig Performance

Abatching/displacementpig’sperformancecanbedeterminedbyseveralmethods:

A. Pigonoroffstream.

B. Lengthofinterface.

C. Amountofcontaminationatinterface.

D. Reducedcorrosion.

• 37

1.0 Introduction

Inlineinspection(ILI)techniqueshavebeenusedsincethe1960stohelpassessintegrityofpipelines.Whilenotarequirementthiswasthebestmethodtodeterminewhetherapipelinewasfit-for-service.In2001,theUnitedStatesOfficeofPipelineSafety(OPS)introducednewfederalrulesandregulationsrequiringliquidpipelineownersandoperatorstoinspecttheirlinesfordefectswhichcouldcausefailuresinhighconsequenceareas.Twoyearslater,theOPSextendedtheseregulationstoincludenaturalgaspipelinesystems.

Stringentregulationscalledforpipelineownerstomakeintegrityassessmentsusinghydrostatictesting,ILIorDirectAssessment(DA).MostoperatorselecttoutilizeILItoolssincetheyprovidedetailedinformationaboutthepipeline’scondition.PrescriptiverepairsbasedonILIdatawereestablishedincludingimmediate,60-dayand180-daytimeframesforhazardousliquidsoperatorsandimmediate,one-yearandmonitoredfornaturalgastransmissionoperators.ThetwoprimaryusesofILItoolsaretodetectandquantifyborechanges(suchasdents,ovalitiesandexpansions)andmetalloss(suchascorrosionandgouging).From1990through2009,excavationdamage,whichincludesthirdpartydamage,accountedfor20.3percentofallSignificantIncidentsrelatedtoonshorehazardousliquidspipelines;excavationdamageinonshorenaturalgastransmissionlinesequatedto22.0percentforthesametimeperiod.Corrosion,anotherleadingcauseofSignificantIncidentsamongonshorehazardousliquidsandnaturalgastransmission,accountedfor23.6percentand18.6percentrespectivelyofallincidentcauses.SeeFigures66and67formoredetailsonSignificantIncidentCausesforU.S.onshorepipelines.Whilethislevelofhistoricaldetailisnotavailableinallregions,similarthreatsareknowntoexistwhichindicatetheneedforassessmentstosecurepublicsafetyandprolongassetlife.

2.0 Preparing the Line

Pre-surveypreparationsshouldnotbecurtailedinanattempttoreducetheoveralltimeandthecostofasurvey.Thisisinvariablycounter-productivebecausearerunisalltoooftenrequired,whichimmediatelyeliminatesanygainsthatmayotherwisehavebeenmade.

Waxdeposits,ferrousmaterialandotherdebriscanaffecttheperformanceofintegrityinspections.Athoroughcleaningprogramisusuallyessentialpriortotheinspectionrun.Thecleanerthepipe,themoreaccuratetheinspectionresults.PleaserefertoSectionIVformoredetailsoncleaningoptions.

Priortorunninganyinspectiontoolitisrecommendedtolaunchagaugingpigtoconfirmpipelinebore.Thisisacost-effectivewaytodeterminewhetherthescheduledinspectiondevicewillbeabletonegotiatetheline.Pipelinesbeinginspectedforthefirsttimearerecommendedtohaveaseparategeometryinspectionperformed.Thisinstrumentedtoolwillconfirmpipelineboreandobtaininformationaboutthegeneralpipelineconfiguration,includingfittingwallthickness,bendradius,degreeanddirection.Gatheringthisinformationonaline

Inline Inspection Technology

S e c t i o n VII I

22.4%

3.9%1.3%

20.9%

20.3%

7.6% 23.6%

SignificantIncidentCauseBreakdownNational,HazardousLiquidOnshore,1990-2009

Source:PHMSASignificantIncidentsFilesOctober29,2010

ALLOTHERCAUSES

CORROSION

EXCAVATIONDAMAGE

INCORRECTOPERATION

NATURALFORCEDAMAGE

MATERIAL/WELD/EQUIPMENTFAILURE

OTHEROUTSIDEFORCEDAMAGE

Fig 66. Pipeline and Hazardous Materials Safety Admin-istration Hazardous Liquids Significant Incident Cause Breakdown for years 1990 through 2009. Significant Incidents are those incidents reported by pipeline operators when any of the following conditions are met: 1) Fatality or injury requiring in-patient hospitalization. 2) $50,000 or more in total costs, measured in 1984 dollars. 3) Highly volatile liquid releases of 5 barrels or more or other liquid releases of 50 barrels or more. 4) Liquid releases resulting in an unintentional fire or explosion.

8.3%

4.4%

2.2%

Source:PHMSASignificantIncidentsFilesOctober29,2010

ALLOTHERCAUSES

CORROSION

EXCAVATIONDAMAGE

INCORRECTOPERATION

NATURALFORCEDAMAGE

MATERIAL/WELD/EQUIPMENTFAILURE

OTHEROUTSIDEFORCEDAMAGE

23.0%

21.7%

22.0%

18.6%

SignificantIncidentCauseBreakdownNational,NaturalGasTransmissionOnshore,1990-2009

Fig 67. Pipeline and Hazardous Materials Safety Administration Natural Gas Transmission Significant Incident Cause Breakdown for years 1990 through 2009. Significant Incidents are those incidents reported by pipeline operators when any of the follow-ing conditions are met: 1) Fatality or injury requiring in-patient hospitalization. 2) $50,000 or more in total costs, measured in 1984 dollars. 3) Highly volatile liquid releases of 5 barrels or more or other liquid releases of 50 barrels or more. 4) Liquid releases resulting in an unintentional fire or explosion.

• 38

notpreviouslyinspectediscriticaltothesuccessofsubsequentinspections.Incaseswherethelinehasbeenpreviouslyinspectedagaugingpigrunmaybesufficientpriortolaunchinganinspectiontool.Theinspectionserviceprovidercanassistindeterminingbestpathforwardtohelpensurethetoolrunissuccessful.

3.0 Inline Inspection

Inlineinspectionservicesutilizean“intelligentpig”toprovideinformationaboutthepipeline.Inspectiontoolswillmeasureandrecordboththemagnitudeandthepositionofanomaliesorfeaturestheyaredesignedtodetect.Thesetoolswillbeusedtoinspectthelinewhileitisinservice.TheILItoolgathersthedatawhichistheninterpretedbytechniciansoranalyststodevelopareportontheconditionoftheline.

TheinformationprovidedbytheseILIservicescoversawiderangeofpipelinefeatures.Thetwomostcommonaremetalloss,includinginternalandexternalcorrosion,andgeometricanomaliessuchasdents,ovalitiesandpipelineexpansions.Otherpipelinethreatsincludelongitudinalseam-weldanomalies,longitudinalfeaturesinthepipebody(i.e.gouging)andstresscorrosioncracking.

4.0 Survey Selection

Onceriskrankinghasbeenperformedincludingpipelinesegmentsrequiredforinspection,threatidentificationforeachsegment,HighConsequenceArealocations,etc.thenextstepistodrafttherequirementsorscope-of-workfortheinformationrequired.ManyILIcompaniescansupportbuildingtheinspectionrequirementsifnecessary.Thescope-of-workcanthenbematchedwithtechnologycapabilitiesandserviceproviders.

Havingdeterminedthetypeofsurveyrequired,theselectionoftheindividualpigorservicecompanytocarryoutthesurveywilldependonanumberoffactors:

• Thepipelinespecifications,whencomparedwithvarioustoolspecifications,willautomaticallyeliminatesomeoptions.Wherethepigspecificationsareclosetotherequirements,orwheresomeparticulardataisunpublished,itisrecommendedtocontactthesupplierforclarification.Frequently,intelligentpigscanbeeasilymodifiedtomeetaparticularrequirement.

• Assumingthereismorethanoneinstrumentedpigwhichseeminglymeetstherequirements,thereareanumberofotherconsiderationssuchastrackrecordoftheserviceprovider,levelofcustomerservice,availabilityandaccuracyofresults,andtheoverallcostoftheinspection.

CompletionofaPipelineQuestionnaire,whichrequestsspecificinformationaboutapipelinerequiringinspection,istypicallythenextstageinthesurveyselectionprocess.Examplesofpertinentinformationincludepipelinediameter,lengthofline,wallthicknesses,producttype,pressure,flow,bendradius,launcherandreceiverdimensionsandsoon.Whiletheinformationrequestedbytheinspectioncompanymayseem

• 39

excessive,thedataisextremelyimportanttohelpingensurefirstrunsuccessandaccuracyofresults.AsamplequestionnaireiscontainedinAppendixII,whichincludesallinformationrequiredpriortoaninspection.

Understandingthethreatstoagivenpipelineisrequiredinordertoensuretheappropriatetechnologyisselectedforidentificationofthosethreats.Thefollowingsectionswilldetailspecificinspectiontechnologiesandtheircapabilities.

5.0 Geometry Inspection

Apipelineisapressurevesselandissubjectedtorelativelyhighstresslevelsandoftentocyclicpressures.Beingburiedprovidesahighlevelofprotection,butitcannotprovidecompleteprotection.Therearenaturalhazardssuchasearthquakes,landslides,subsidenceandfloods.Therearealsothemorecommonriskssuchasthirdpartydamage.

Anyoftheseeventsmaycausephysicaldamage,resultingindents,buckles,gougesetc.,buttheyrarelycausethelinetoruptureimmediately.Mostly,theyresultindeformationoftheline.Suchdeformationsmayhavegraveconsequencesoveraperiodoftime.Therefore,itisvitallyimportantthateverysignificantdeviationfromtheoriginalshapeofapressurevesselisinvestigated.Toinvestigatethesedeviations,itisnecessarytofindthem,andthisisthemainpurposeoftherangeofpigswhicharedesignedtolocateandmeasurereductionsindiameter.Furthermore,U.S.regulationsrequireremediationofdentsviaprescriptiverepaircriteria.

5.1 Gauging Pigs

Thegaugingpighasbeenusedformanyyearstoverifyreductionsintheinternaldiameter.Thisisacleaningpigequippedwithamildsteeloraluminumplate.Gaugeplatesaremachinedtoapercentage,commonly95percent,ofthenominalinsidediameterofthepipeline.Itisimportanttonotethattherearenoodometers,sensorsorelectronicsonboardthetool.Thisisabasicmethodtoprovepipelinebore.Ifthepigisremovedfromthereceiverwithdents,scratchesorotherabrasionstotheplate,measurementsaretakentodetermineiftheminimumboreasdetectedbythegaugeplateissufficientforinspectiontoolpassage.Apigthatsuccessfullynegotiatesthepipelinewithoutdamagetotheplateisassumedtorevealthepipelinedoesnothavereductionsindiametergreaterthanthepredeterminedpercentageamount,andsafepassageofsubsequentinspectiontoolsisexpected.Insomecasesadamagedgaugepigrunmayresultintheneedtomakeaseparategeometryinspectiontobetterunderstandwhatcauseddamagetothegaugeplate.AgaugingpigisshowninFigure68.

5.2 Geometry Tools

Geometryinspectionsareperformedtoidentifychangestotheinternaldiameterofthepipelinecausedbyovality,dents,partiallyclosedvalves,changesinwallthickness,etc.Geometrytoolsweredesignedtoaccuratelydetectandquantify

Fig 68. Gauging Pig

• 40

thesechangesinpipelinebore.Thesetoolsareequippedwitharms,orfingers,whicharespringloadedinordertokeepthempressedagainstthepipewall.Theymayeithercontactthepipewalldirectly,orindirectlybybeingmountedinsidethedrivecupattherearofthetool.Anychangeindiametercausesthesearmsorfingerstomovemechanically.Thesemovementsarethenrecordedinonboardelectronicsalongwithodometerinformationforsizingandlocationoftheanomaliesalongthepipeline.

TheTDWKALIPER®pigwasintroducedinthe1960stoovercometheuncertaintiesleftwhenusinggaugepigs.Itusedanodometerwheeltomeasurethedistancetraveledandastylustoindicatetheextentofthedentdamage.Skilledanalysiscouldnotonlyprovideameasureofthereductionbutalsoareliableestimateofitsshapeandphysicallocation.

TheKALIPERtechnologyhasbeencontinuouslyadvancedtoincreaseperformanceandresolution.TheKALIPER360,showninFigure69,containsanelectronicpackageandcomputeranalysisthatgreatlyenhancesboththeaccuracyandlevelofdetailreportedversustheoriginalKALIPERtechnology.Thistechnologywillreportthelocation,clockorientationandseverityoftheanomalydetectedwithintwopercentoftheoutsidepipediameter.KALIPER360wasprimarilydesignedforuseinnewconstructiongeometryapplicationstoprovepipelineboreafterconstruction.Itssingle-body,lightweightdesignispropelledeasilywithcompressedairafterhydrostatictestingofnewlyconstructedpipelines.

5.3 Deformation Tools (DEF)

Deformationtoolsprovideanunparalleledlevelofaccuracyinmeasuringdentsandovalitiesthatrivalshandmeasurements.Thesetoolsalsodetectandaccuratelysizeothercrucialanomaliessuchaspipeexpansionsandgirth-weldmisalignments.ExamplesofgeometricanomaliesareprovidedinFigures70through71b.

Eachlineonthegraphisindicativeofasensororarmonthetool(refertoFigure73forviewoftoolconfiguration).Dataontheleftrevealsthedentasdepictedinrawdata.Thecross-sectionontherightshowsvariousdiameterreadingsandminimumboreatthedentlocation.Notethedentappearstobeat7o’clock.Deformationdataprovidesdetailssuchasminimum,averageandmaximumbore,calculatedwallthickness,orientation,individualarmdeflection,etc.atanyprescribeddistanceinterval.

Thetopexampleshowsasectionofthreejointsoflargediameterpipe.Thejointinthecenterexhibitsanincreaseintheinsidediameterofthepipethatreachesamaximumdiameternearthedownstreamgirthweld.Theoutwardmovementofthesensorarmsisnotedbyanupwarddeflectionofthetracesandalighteningofthebackgroundgrayscale.Theincreaseddiameterendsabruptlyatthegirthweld.Thecross-sectiononthebottomshowstheexpandedpipeorientationfrom10o-clockto4o’clockaroundthecircumference.Theorangecirclerepresentsnominalinternaldiameterwhilethebluerepresentsactualinternaldiameterdue

Fig 69. KALIPER® 360 Geometry Inspection Tool

Fig 70. Dent from High Resolution Deformation Tool

Fig 71a. Expanded Pipe

Fig 71b. Expanded Pipe

GirthWeld

Areaofnominalpipe

GirthWeld GirthWeld GirthWeld

Areaofexpanded

pipe

• 41

Fig 73. Deformation Tool: each arm rides independently and travels along the internal diameter with direct pipewall contact.

Fig 72. Dent strain analysis. DEF inspection data provides high-quality representation of dent shape. Local dent strain can be estimated by analyzing the deformed shape.

toexpansionatthelocation.

DifferingfromKALIPER360,measurementarmsridedirectlyontheinternalpipewallratherthanbehindacupforincreasedsensitivity.Armspacingisalsosignificantlytighter,averaging0.50incheswhencontractedintheinternaldiameter.Highresolutiondatafromthesetoolsisalsoutilizedforinducedmaterialstrainanalysis,asshowninFigure72.

DEFtechnologycanbejoinedwithothertoolstoobtainmultipledatasetsfromasingleinspection.ADEFtoolisshowninFigure73.

6.0 Metal Loss Inspection

Corrosionisoneofthemostcommonpipelinethreats,nexttoexcavationdamage,andcanbecategorizedintwomainareas:internalandexternal.Externalcorrosionmayresultfromdisbondedcoatingsorcoatingdamage,straycurrents,inadequatecathodicprotectiontonameseveral.Internalcorrosioncausesarelinkedtodebris,waterandothercorrosivecontaminants.Billionsofdollarsarespentannuallytomitigatecorrosionanditscause.Utilizingadvancedinstrumentedtoolsformetallossinspectionisacriticalcomponentofapipelineoperator’sintegritymanagementprogram.

ThetwomaininspectiontechniquesusedtodetectandquantifycorrosionareMagneticFluxLeakage(MFL)andUltrasonics(UT).TheseapproachestometallossinspectiondifferinthatMFLisanindirectmeasurementofamagneticfieldwhileUTisadirectmeasurementofthepipewall.Eachhasitsadvantagesanddisadvantagesasaresult.Somearelistedbelow.

SizingAccuracy:

• UTsizingtolerancesaretighterthanMFLduetodirectmeasurementtechnique

LineCleanliness:

• PipelinecleanlinessiscriticaltosuccessfulinspectionthoughUTrequirescleanlinesstoanextremelyhighlevelforaccurateinspection

InspectableWallThickness:

• UThasdifficultyinspectinglowerwallthicknesswhileMFLmayhavedifficultywithsignificantlythickwalldependingonpipediameter

ToolVelocities:

• MFLgenerallyhasnominimumvelocityspecificationandcanberunupto7mph(3m/s)whileUTrequiresveryslowspeedsrangingfrom0.2to2mph(0.1to1.0m/s)

Couplant:

• MFLrequiresnocouplant,thusitcanberuninamultitudeofinspectionmediums.UTrequiresacouplantsimilartoaUTprobe,whichlimitsapplication.

MFLwillbedetailedinSection6.1.

Directionofflow,topofpipe

• 42

6.1 Magnetic Flux Leakage (MFL)

MFLtoolshavebeenusedtoinspectpipelinesformetallosssincethe1960s.Atthattimeonlythebottomquadrantwasinspected.Thetechnologyadvancedtoincludefullcircumferenceinspectionalongwithdepthrangesofanyindicatedmetalloss.Thisrobusttechnologycontinueditsevolutiontoincludeanomalydimensionssuchasdepth,lengthandwidth;increasedsamplingdistance,sensorcount,resolutionandinspectionranges;andlatertheabilitytobecombinedwithothertechnologiessuchasdeformationtoolsforenhancedanalysisandoperationalimprovementsforthepipelineowner.

Thetechnologyworksbyinducingmagnetismintothepipewallto“saturation.”Sensorsorientedwithinthemagneticfieldthendetectanychanges.Iftherearenoconditionsthatdisturbthefieldno“leakage”occurs.Whenthefieldisdisturbedthesensorsorientedwithinthefielddetectthechangesandrecordtheinformation.Thisinformationisstoredonboardthetoolandlaterdownloadedforanalysis.Allchangesinthemagneticfieldarerecorded,includinggirthwelds,valves,fittings,metalloss,extrametal,casingsandotherpipelinefeatureswithferrouscharacteristics.Metallossisalsocategorizedbetweeninternalandexternalanomaliesviaasecondarysetofsensorsspecificallydesignedforthispurpose.SeeFigure74formoredetailsonthemagneticfield.

HistoricallyMFLtoolsweredesignedwithasolidmagnetizerusingwirebrushestoinducemagnetism(seeFigure75).

Solidmagnetizersworkwellinliquidlines,areabletonegotiate1.5Dbendsandgenerallyhavetheabilitytonegotiateupto15%reductions.Thisdesign,however,hasnotbeenconducivetosuccessfullyinspectingnaturalgaspipelinesduetothedragandfrictioncreatedbythedesign.Therefore,anothermagnetizerdesignexistsforinspectingpipelinesincompressiblemediums(seeFigure76).Thisdesignallowsforupto25%reductioncapabilityandsignificantlyreduceddragduetoitscollapsiblenatureanduseofskidplatestotransfermagnetismversus

Fig 74. Magnetic Flux Leakage Principle: (A) magnets are oriented in opposing poles to create a magnetic

current. (B) mechanism used to transfer magnetism into the pipewall, usually wire brushes or skid plates. Refer to

Figures 75, 76, 77 and 78 for more details on types of magnetizers and how they appear on a physical ILI tool.

Fig 75. Solid Body Magnetizer: note the fixed body design, wire brushes to transfer magnetism and ring of

sensors mounted around circumference.

Fig 76. Collapsible (floating) Magnetizer. On right: note the separate magnetizer bars with plates to transfer

magnetism; each bar contains its own sensors. On left: cross-section view showing collapsibility once the tool is

inserted into the pipeline.

• 43

Fig 77. MFL Tool with Fixed Brush Magnetizer

Fig 78. MFL Tool with Collapsible Magnetizer

Fig 79. Patch of Metal Loss Detected by an MFL Tool.

wirebrushes.Asaresult,lesspressureisrequiredtomovethetool.Thiscreatesamoreconsistentvelocityprofileandhelpseliminatespeedexcursionsoutsideoftheupperlimits.Theresultissuccessfulmagnetizationofthepipewallandaccuracyinthereporteddata.ActualphotosofeachtoolcanbefoundinFigures77and78.

7.0 Seam Weld Inspection and Other Longitudinally Oriented Anomalies

Insufficientqualityandmanufacturingpracticesofpipebuiltpriorto1970hascreatedintegritythreatsoutsideofdeformationsandmetalloss.Longitudinalseamweldanomaliessuchaslack-of-fusionandhookcrackshaveresultedinflawsthatgoundetectedbyMFLortraditionalUT,andmanyhaveresultedinleaksorruptures.Additionally,therearevariouslongitudinallyorientedanomaliesthatgoundetectedinMFLduetotheirorientationtotheaxialmagneticfield.

InSection6.1theMFLtechniquewasdiscussedindetail;magnetismisinducedinthepipewall,changesinthepipewalldisturbthemagneticfieldandsensorsorientedinthefieldrecordthechanges.Anomaliesthatarenarrow;i.e.littleornowidtharoundthepipecircumference,andlongitudinalinnaturecangoundetectedbyMFL.ThiscanoccursimplybecausethereisnotenoughwidthtodisturbtheaxialmagneticfieldinducedbyMFLtools.AsaresulttheMFLtechniquewasmodifiedtoorientmagnetismtransversely,orcircumferentially,tobisectlongitudinalfeaturesandthuscreatethe“leakage”requiredtodetectsuchanomalies.RefertoFigure80.

Fig 80. Axial MFL is excellent at detecting volumetric flaws or anomalies with circumferential width. Longitu-dinally oriented anomalies can go undetected by axial MFL. Circumferential or transverse MFL was developed to detect those anomalies oriented longitudinally and narrow in width.

AxialMFL

NotDe-tected

Detected

CircumferentialMFL

• 44

Fig 81. TFI: Magnetism induced circumferen-tially between poles as depicted here creates inspection gaps where magnets are located.

An offset magnetizer is required to ensure one-hundred percent coverage is achieved.

Fig 82. SMFL: Magnetism induced diago-nally or spirally along the pipeline. This design facilitates one-hundred percent

coverage with a single magnetizer.

Fig 83. SMFL and MFL magnetizers com-bined for superior seam assessments and

metal loss inspection with a single tool.

7.1 Transverse Field Inspection (TFI)

TFItoolsweredevelopedtodetectlongitudinallyorientedanomalies.Thesetoolsinducemagnetismataninety-degreeangle,orcircumferentially,ratherthanalongtheaxisaswithMFLtools.Thisdesignallowsfordetectionofseamweldandotherlongitudinalanomalies,thoughitsdesigncreatessomedisadvantages.Inordertoinducemagnetismaroundthecircumference,andachieveone-hundredpercentcoverage,twooffsetmagnetizersmustbeutilized.Thismakesforalongertoolandwouldrequiremultipleinspectionsifthereisaneedformetalloss,deformationandlongitudinallyorientedanomaliesinasingleinspection.SeeFigure81.

7.2 Spiral Magnetic Flux Leakage (SMFL)

Aninnovativeapproachtodetectingseamweldandlongitudinalanomaliesinthepipe-bodyresultedinSMFL.Thistechnologyprovidesassessmentofthelongitudinalpipeaxisinasinglecompactmagnetizer(seeFigure82).ThebenefitiscompleteassessmentoflongitudinalanomaliesanditsabilitytobecombinedwithMFLforsuperioraccuracy(refertoFigure83).InmanycasesTFIwillindicate“crack-like”or“possiblecrack-like”anomalies,causingthepipelineoperatortomakeverificationdigs.WhenpairingSMFLwithMFLthereisextremeclaritybroughttoseamdefectsandwhethertheyaretruly“crack-like”,i.e.lackoffusion,hookcracks,etc.(seeFigure84).TheseenhancedresultsbroughtaboutbyfusingMFLandSMFLdataresultsinreducedexcavationsforthepipelineoperatorandthussignificantcostssavingsrelativetostand-aloneTFI.

8.0 Geometry, Metal Loss, Long-Seam, Longitudinal, Hard Spot Inspection

Untilrecently,inspectingforvariouspipelinethreatsrequiredmultipleinspections.Withinthelasttenyears,combiningdeformationwithMFLbecamethestandardformanyinspectionserviceproviders.Theseadvancementsassistedboththeinspectioncompanyandpipelineoperator.Theserviceprovideronlyhadtomanageonetool,andintegratingbothdatasetsintoasinglefinalreportenhancedtheanalysisprocess.Forthepipelineoperator,theyonlyneededtoscheduleproductforoneinspectionandtrackasingletool,amongotherbenefits(seeFigure85forexampleofadeformationandMFLcombinationtool).

Whenanoperatorrequiredgeometry,metallossandseamassessments,multipleinspectionswerestillrequired.Thatis,untilrecentdevelopmentsincreatingamultipledatasetplatformthatcanincludeDeformation,MFL,SMFLandResidualsensorsfordetectionofhardspotsandmechanicalstrain.Combiningthesedatasetsonasingletoolbuildsuponthebenefitstoboththeinspectioncompanyandpipelineoperatorasdescribedpreviously.Notonlyaregeometry,metalloss,long-seamandstrainanomaliesdetectedandreported,analyzingalldatasetsfromasingleinspectionproducessuperiorresultscomparedwithperformingindividualinspections.

• 45

MFL SMFL

Fig 84. Data from an MFL+SMFL inspection. MFL data on the left indicates two slight metal loss anomalies. The SMFL data on the right confirms those two anoma-lies but also reveals a planar seam-weld feature that is not detected in MFL.

Fig 85. Example of a “combination tool” with deforma-tion and MFL datasets.

• 46

RES

SMFL

DEF

MFL-ID/OD

Forexample,Figure86,isindicativeofthebenefitsofutilizingamultipledatasetapproach.Additionalstraincausedbyapotentiallyinsignificantdentbydepthpercentagecanimpactprioritizationofsuchanomalies.OntopoftheidentifiedstrainisconfirmationofmetallossinthedentfromtheSMFLdata.DuetothenatureofthemetallossshapeitisnotdetectedinMFL(referbacktoSection7.0fordetailsonthissubject).Figure87showsanexampleofamultipledatasettoolusedtoprovidethedatarepresentedinFigure86.

9.0 Crack Inspection

Crackingcancomeinmanyforms,suchasstresscorrosioncracking(SCC),andgoesundetectedbyanyofthepreviouslymentionedtechnologies.Themostcommonlyused,andwidelyaccepted,technologyforcrackdetectionisUltrasonicTechnology(UT).ThesameoperationalrequirementsexistaswithUTtoolsformetallossinspection,includinglinecleanliness,toolvelocityrangeandrequiredcouplant.UTcracktoolsdifferfromUTmetallossinspectiontoolsmainlyintheangleofthetransducer.AnemergingtechnologyforcrackdetectionisElectromagneticAcousticTransducer(EMAT).

WhileimplementationofEMATtechnologyisdifferentfromUTtheapproachissimilar:transmitasonicwaveintothepipewalltodetectcracking.UTutilizesapiezoelectrictransducertoimpartasonicwavetoamaterialthrougha“mechanical”couplant.Iftheacousticwaveisaltered,areflectionoccursandareflectedwaveindicatesananomalyispresent.UTtransducersimpartandmeasurethesonicwaveandreflections.EMATreliesonaninteractionbetweenamagneticfieldandawirecoiltoimpartasonicwavewithinthepipewall.Eddycurrentscreatedbythewirecoilinteractwithmagneticfieldtoimpartsonicwaveswithintheinspectedmaterial.Iftheacousticwaveisaltered,areflectionoccursandareflectedwaveindicatesananomalyispresent.EMATsensorsetsutilizetransmittersandreceiverstoimpartandthenreceivethereflectedsignals,re-spectively.Figure88graphicallydepictsthedifferencebetweenUTandEMAT.

10.0 Pipeline XYZ Mapping

Submetermappinginformationforapipelinecanbeextremelyvaluable.Usesincluderefininggeographicinformationsystem(GIS)data,pipelinedisplacement,bendingstrain(Figure89)andpinpointlocationofanomaliesinthefield.Dataisprovidedviaanonboardinertialmeasurementunit(IMU)inconjunctionwithanabove-groundsurvey.Controlpointsmustbeestablishedalongthepipecenterlinetrajectoryspacedatperiodicintervalsbetweenthelauncherandreceiver.Thesecontrolpointsareusedtoprovidecoordinateupdatestoaidthefinalprocessingoftheinertialdatagatheredfromtheinstrumentsonboardtheinspectionvehicle.

Fig 86. Data from a multiple-dataset tool; dent with metal loss. First from top left reveals dent with mechanical strain in Residual Data; top right is the deformation data showing the dent in raw data and orientation in the cross-section view; bottom left is MFL data inclusive of ID/OD data which also depicts the dent but does not show metal loss; bottom right screen from left is the SMFL data which reveals the long-seam and the dent; note that in this view metal loss in the dent is confirmed.

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Fig 87. 10-inch multiple dataset tool. From right to left: drive section including odometers, Spiral MFL, Deformation with IDOD Sensors, MFL and Residual Sensors (SMFL+DEF+IDOD+MFL+RES).

Fig 88. Ultrasonic Technology (UT) versus Electromagnetic Acoustic Transducer (EMAT)

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Mostcontrolpointswillalsoserveaslocationsfortooltrackingbymeansofabovegroundmarkers(AGMs).

Forinspectionstoberunattoolspeedsatorabove1m/s(3.3ft/s),selectcontrolpointlocationsspacednomorethan2km(1.24mi)apartalongthepipecenterlinetrajectory.Forinspectionsslowerthan1m/s(3.3ft/s),selectcontrolpointlocationsspacedsuchthatthetoolwillpassacontrolpointevery20to30minutes.Closerintervalswillimprovetheaccuracyofthedataprovided.Whenselectinglocationsandconsideringsurveystrategiesateachlocation,rememberthattheeventualcoordinatesofinterestarelocatedalongthecenterlineofthepipeline.

Requiredlocations:

• Launcherdoor,upstreamweldoflauncherreducer,andlaunchervalve

• Receiverdoor,downstreamweldofreceiverredu

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