Analysis of Natural Gas Transmission Pipeline Releases and ...

AnalysisofNaturalGasTransmissionPipelineReleasesandMitigationOptionsforPipelineMAOPReconfirmation

March,2017

Preparedfor:TheInterstateNaturalGasAssociationofAmerica(INGAA)Preparedby:ProcessPerformanceImprovementConsultants,LLC(P-PIC)

AnalysisofNaturalGasTransmissionPipelineReleasesforPipelineMAOPReconfirmationandMitigationOptions

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Acknowledgement

Theobjectiveofthisreportistoanalyzethehigh-levelimpactofnaturalgastransmissionpipelineMAOPreconfirmationasoutlinedinthePipelineandHazardousMaterialsSafetyAdministration(PHMSA)“SafetyofGasTransmissionandGatheringPipelinesNoticedofProposedRulemaking”(NPRM),issuedbyPHMSAandpublishedintheFederalRegisteronApril8,2016.P-PIC’sanalysisprovidesanoverviewofthepotentialnaturalgasreleasesconnectedtoaspectsoftheNPRMandreviewscalculationsandmitigationoptionsoutlinedinthePHMSAPreliminaryRegulatoryImpactAnalysisandtheM.J.Bradley&Associatesreport“PipelineBlowdownEmissionsandMitigationOptions,”preparedfortheEnvironmentalDefenseFundandthePipelineSafetyTrustinJune2016.P-PICdevelopedhigh-levelmodelstorecalculateaspectsofmileageandpotentialgasreleases,derivedfromasubsetoftransmissionoperatorsrepresentingasignificantportionofinterstatenaturalgaspipelinemileageintheU.S.andfromasetofassumptionsbasedonoperatorinputandserviceproviderfeedback.Noinformationshouldbeattributedtoasingleoperatororserviceprovider,butinsteadshouldbeattributedtothemajorityofinterstatenaturalgaspipelineoperations.Participationinthisstudydoesnotimplyagreementwiththestudy’sconclusions.Wethankalloperatorsandserviceprovidersforprovidingdatausedinthisanalysis.

TableofContents

1.Summary.........................................................................................................41.1PHMSABlowdownCalculations.......................................................................................................61.2M.J.BradleyReportCalculations.....................................................................................................71.3P-PICAnalysisandModelingMethodology................................................................................81.4RecalculatingBlowdownMileageEstimate.................................................................................91.5EstimateofTotalGasReleaseWithoutMitigation...............................................................121.6EstimatedTotalGasandMethaneReleaseCalculations....................................................141.7ComparisonofMethaneReleaseCalculations........................................................................162.0InterstateMitigationOptionAnalysis..........................................................172.1Flaring......................................................................................................................................................202.2PressureReductionwithIn-LineCompressors.....................................................................212.3PressureReductionwithMobileCompressors......................................................................222.4LowPressureDiversion...................................................................................................................232.5Stopples...................................................................................................................................................23

3.ResultsofAnalysis.........................................................................................24

ListofTables

Table1:PHMSAMAOPReconfirmationMileageReportedinRIA................................10Table2:PHMSAPressureTestandILIUpgradeMileageReportedinRIA.................10Table3:M.J.BradleyMileageUsedInReport.....................................................................11Table4:P-PICMileageToReconfirmMAOPWithoutValve-to-ValveSpacing.........11Table5:P-PICTotalBlowdownWithValve-to-ValveSpacing.........................................12Table6:PHMSAWeightedAveragePipeDiameter(inches)...........................................13Table7:P-PICEstimatedWeightedAveragePipelinePressure(psi)...........................14Table8:P-PICEstimatedTotalGasRelease.........................................................................16Table9:EstimatedMethaneReleaseComparisonOver15Years...............................16Table10:P-PICEstimatedMileageforMitigationOptions(Interstate)......................18Table11:P-PICEstimatedGasReleasedwithMitigation(Interstate).........................19Table12:P-PICEstimatedTotalVolumeofMethaneReleasesfrom...........................19ReconfirmingMAOP......................................................................................................................19

1.SummaryThePipelineandHazardousMaterialsSafetyAdministration(PHMSA)publishedits“SafetyofGasTransmissionandGatheringPipelinesNoticeofProposedRulemaking”(NPRM)1andPreliminaryRegulatoryImpactAnalysis(PRIA)inApril2016toaddresscongressionalmandatesfromthe2011PipelineSafety,RegulatoryCertainty,andJobCreationAct2andsubsequentrecommendationsfromNationalTransportationBoard(NTSB)andU.S.GovernmentAccountingOffice(GAO).ThePRIAjustifiestheNPRMbyprovidingthatitssocietalbenefitsoutweightheannualcostsoftheNPRMtoindustry,whichthePRIAestimatesatapproximately$270-310.8millioninbenefitscomparedto$47.4millionincostsannually.PHMSAgrantedaninitial60-daypubliccommentperiodontheNPRM,thenextendedforanadditional30days,closingonJuly7,2016.Over400commentsweresubmittedtothedocketfromavarietyoftradeorganizations,operators,publiccitizensandnon-governmentalorganizations.InreviewinganddevelopingcommentsontheNPRM,oneofthemajorareasofconcernforthenaturalgastransmissionpipelineindustryfocusedontheNPRM’sproposedrequirementsforreconfirmingmaximumallowableoperatingpressure(MAOP)forcertainpipelinesegmentinHighConsequenceAreas(HCAs),ModerateConsequenceAreas(MCAs),andClass3and4locations.3,4ThemethodsforreconfirmingMAOPspecifiedintheproposedruleincludeahydrostaticpressuretest(“hydrotest”)oraseriesofIn-LineInspections(ILIs)aspartofanEngineeringCriticalAssessment(ECA).IndustrycommentsweregenerallysupportiveofPHMSA’sgoalsinrequiringMAOPreconfirmation.However,extensiverequirementsproposedforECAsintheNPRMmaydiscourageoperatorsfromemployingtheECAapproach,andindustrycommentshavesuggestedthattheMAOPreconfirmationrequirementswillsubstantiallyincreasepressuretestingfornaturalgaspipelineindustryoverthenext15years.5

1PipelineSafety:SafetyofGasTransmissionandGatheringPipelines,81Fed.Reg.20,722(Apr.8,2016)2PublicLaw112-903CommentsoftheInterstateNaturalGasAssociationofAmericaregarding“PipelineSafety:SafetyofGasTransmissionandGatheringPipelines(DocketID:PHMSA-2011-0023),http://www.ingaa.org/File.aspx?id=29912&v=ccaef774(July7,2016).4CommentsoftheAmericanGasAssociationontheSafetyofGasTransmissionandGatheringPipelinesProposedRule,https://www.aga.org/sites/default/files/aga_comments_-_gas_transmission_gathering_lines_nprm_-_july_2016.pdf(July2016).5Id.


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DuringthecommentperiodfortheNPRM,EnvironmentalDefenseFund(EDF)andPipelineSafetyTrust(PST)submittedaM.J.Bradley&Associates(“M.J.Bradley”)studyevaluatingthenaturalgasreleasesconnectedwiththeproposedruleandwaystomitigatethosereleases.6TheM.J.BradleyreportestimatesthetotalvolumeofthegasreleasesthatcouldresultfromhydrostaticpressuretestingtoreconfirmMAOPforcertainsectionsoftransmissionpipeline.7Suchreleases,oftenreferredtoas“blowdowns,”areusedtoremovenaturalgasfrompipelinesegmentssothatpressuretestingcanbecompletedsafely.Inaddition,theM.J.Bradleyreportdescribesavarietyofmitigationmethodstoreducegasreleases:gasflaring,pressurereductionusingin-lineorportablecompressors,gasinjectiontoanear-bylow-pressureline,andapplyingstopplestolimitblowdownmileage.Thereportestimatescostsandbenefitsforeachmitigationmethodandcalculatesthereductioninreleasevolumesassociatedwitheachmethod.ThisreportisintendedtocontinuedevelopingthegasreleaseimpactsontransmissionpipelinesassociatedwiththeNPRM,andrecognizestheworkM.J.Bradleyandothershavemadeinquantifyingthesereleases.Addingmoreoperatorinputandsystemdataintotheanalysisanddiscussinginnovativepracticesandtechnologiesfacilitatescontinueddialogueonthisimportanttopic,andprovidesthebestoutcomeforminimizinggasreleaseswhileaccomplishingtheimportantpipelinesafetygoalsoftheNPRM.P-PICprovidesareviewandanalysisofkeycalculationsandmethodologiescontainedinthePHMSAPRIAandM.J.Bradleyreport.Thereviewincludesevaluatingindustrydatacomparedtothetheoreticalmodelsoutlinedineachreport.Assuch,thisreportdevelopsnewmodelstoquantifythetotalvolumeofgasreleasesassociatedwiththenewMAOPreconfirmationrequirementandaccountsforsystemvariations,mileageimpactsandoperationalconstraints.SelecttransmissionoperatorsprovideddatabyanalyzingpartsoftheirsystemandprovidinginputonthefollowingfactorsrelatedtoMAOPreconfirmation:

• EstimatedHCAandMCAmileagerequiredtoundergoMAOPreconfirmationpertheNPRM

• Estimatedtotalmileagethatwouldundergopressuretestingduetovalve-to-valvespacing

6“AnalysisofPipelineandHazardousMaterialsSafetyAdministrationProposedNewSafetyRules:PipelineBlowdownEmissionsandMitigationOptions,”http://pstrust.org/wp-content/uploads/2015/10/PHMSA-Blowdown-Analysis-DRAFT-FINAL-30jun16.pdf(June2016)7Apipeline“blowdown”isanevacuationofnaturalgasfromthepipelinesegmentthatreducespressureinthatsegmenttoatmosphericpressure.Pipelinesmustbegas-freeandatatmosphericpressuretobeginthehydrotestingprocess.


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• Averagepressureanddiameterdata• Systemcharacteristicsandpercentageoftimemitigationoptionsarenot

feasibleduetosystemconstraintsBasedontheanalysis,P-PICprojectsthatthegasreleaseestimatescontainedinPHMSA’sPRIAandtheM.J.BradleyreportunderestimatethetotalvolumeofgasthatwouldbereleasedfortransmissionoperatorstocomplywiththeMAOPreconfirmationrequirement.ThekeyconclusionsofP-PIC’sstudyinclude:

• Substantiallylargergasrelease—OperatorswillusepressuretestsastheprimarymethodforreconfirmingMAOPunderPHMSA’sNPRM,andvalve-to-valvespacinggreatlyimpactstotalpressuretestmileage.Therefore,P-PICestimatesthatthetotalvolumeofgasreleasesforMAOPreconfirmation,beforemitigation,wouldbeapproximately25timesthatreportedinthePRIAandtheM.J.Bradleyreport.

• Mitigationoptionsdohavelimits—TherearefivemitigationoptionsoutlinedintheM.J.Bradleyreportthatoperatorsmayemploywhenpracticableandcost-effective.However,notallblowdownscanbemitigated,andmitigationoptionsmaynotrecoverallofthegaswithinapipeline.

1.1PHMSABlowdownCalculationsPHMSAconductedacostandbenefitanalysisoftheNPRM,whichoutlinedtheamountofmileageimpactedbytheproposedrequirementtoreconfirmMAOP.ThePreliminaryRegulatoryImpactAnalysis(PRIA)contendsthatatotalof11,757milesofpipelinewouldneedMAOPreconfirmationand,ofthat,3,148mileswouldrequireapressuretestorILIupgradethatwouldincludeablowdown.8PHMSAestimatesthat3,148milesofblowdownswouldrelease62,216MCFofmethaneintotheatmosphereeachyear,whichcorrespondsto65,012MCFperyearofnaturalgasreleases,asmethaneisnottheonlycomponentofnaturalgas.9Thisnumberwascalculatedbyusingaweightedaveragediameterofpipelineandassumesa400poundspersquareinch(psi)averageoperatingpressureforinterstateandintrastatepipelinesandaweightedaveragediameterof22.0inchesforinterstatepipelinesand15.2inchesforintrastatepipelines.PHMSAmultipliedthevolumeofnaturalgasreleasesperyear(65,012MCF)by15yearstogeneratethetotalvolumeofmethanereleasesover15years;thisappearstobeanerror.

8PHMSApressuretest(PT)andILIUpgrademileageforinterstateandintrastatearefoundinTable3-50and3-54(page.64and65ofthePRIA).9SeeTable3-55:TotalEmissionsPerYearfoundonpage65inthePRIA.


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PHMSAshouldhaveuseditsestimateforthevolumeofmethanereleasesperyear(62,216MCF)forthiscalculation.ThesecalculationsassumethatreconfirmingMAOPforonemileofpipewillonlyrequireonemileofpipetobeblowndown;thesecalculationsdonotaccountforthevalve-to-valvemileagethatmustbeisolatedtoaccommodateahydrotestorILImodifications.PHMSAalsosubtractsbaselineintegrityassessmentmileagefromtheestimatedtotalmileagerequiredtoreconfirmMAOPtoestimatethenetblowdownmileageassociatedwiththeNPRM.

1.2M.J.BradleyReportCalculationsTheM.J.Bradleyreportoutlinesaslightlydifferentmileageestimate.ThereportusesthePHMSAtotalmileageforpressuretestwithoutsubtractingoutthebaselineintegrityassessmentmileage.Assuch,thetotalmileageusedintheM.J.Bradleyanalysisis3,509totalmilesforinterstateandintrastatethatwouldincludeapressuretestorILIupgrade.TheM.J.Bradleyreportrecognizesthehighlyvariedsystemandoperationalparameters,suchasdiameterandoperatingpressure,whichsignificantlyimpacttheoverallvolumeofgasreleases.M.J.BradleyreviewedPHMSA’smethodologyandagreeswiththeiroverallapproach;however,M.J.BradleycaveatsthattherearemanyuncertaintiesthatPHMSA’sPRIAdoesnottakeintoaccount,includingaveragepressureandaveragelengthofblowdownsegments.ToestimatethetotalvolumeofgasreleasesassociatedwiththeMAOPreconfirmationrequirements,M.J.BradleyutilizesPHMSAannualreportdatatodeterminetheaveragepipediametersforinterstateandintrastatepipelines.Table2intheM.J.Bradleyreportillustratesthediametersusedintheircalculationandtheweightedaverageofthosediameters.SimilartothePHMSAPRIA,theM.J.Bradleycalculationsuseanaveragediameterof22inchesforinterstatesystemsand15.2inchesforintrastatesystems,anda400-psiinitialpipelinepressurevalue.TheM.J.Bradleyreportrecognizesthatthispressureestimatemaybeunsupportedduetoalackofavailabledataonaverageinterstateandintrastatesystempressures.However,thereportdoesprovidearangeaslowas200psiupto1500psi.TheM.J.BradleyreportestimatesthatreconfirmingMAOPwillresultin20,291metrictons(1,060,657Mcf)ofmethaneovera15-yearperiod.Additionally,theM.J.BradleyanalysisidentifiesfivemitigationmethodstoreducegasreleasesassociatedwithblowdownsforMAOPreconfirmation,andsuggeststhatemployingoneormoreofthesemethodsmayreducemethanereleasesby


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50%-90%.Themostcosteffectivemethodidentifiedinthereportisusingin-linecompressionortransferringtoalow-pressuresystem.

1.3P-PICAnalysisandModelingMethodologyPHMSA’sPRIAunderestimatestheamountofmileageimpactedbytheNPRMwhenimplementingtherequirementswithintheMAOPreconfirmationtopicarea.ThePRIAassumesoperatorswouldoverwhelminglyuseILIstoreconfirmMAOP.TheNPRMwouldallowMAOPreconfirmationusing“Method3,”whereoperatorscouldutilizeECA,incorporatingdatafromILIruns,inlieuofpressuretesting.However,industrycommentershavegenerallysuggestedthattheECAapproachproposedintheNPRMisoverlycomplicated,burdensome,andimpracticable.10,11Therefore,theamountofpipethatwouldexperienceblowdownsforpressuretestingwouldfarexceedPHMSA’scalculations.Additionally,PHMSAsubtractsmileageforotherbaselineintegrityassessmentprogramsfromitsestimatesforMAOPreconfirmationblowdownmileage.IndustrycommentershavesuggestedthathydrotestsforMAOPreconfirmationwouldbeaccomplishedonadifferenttimelineandprocessthanbaselineintegritymanagementassessments.12MAOPreconfirmationisaone-timeactivitywiththegoalofconfirmingpipelinematerialstrength,whereasintegritymanagementisacontinuousprocessdesignedtoevaluateandmitigatetherangeofongoingthreatstoaspecificpipeline.ThemajorityofbaselineintegritymanagementassessmentsutilizeILI,nothydrotesting,soMAOPreconfirmationwouldlikelybeanentirelyseparateprogram.Assuch,INGAAcommissionedaseparatesurveyofitsmemberoperatorstoestimatetheamountofmileagethatwouldbeimpactedbytheMAOPreconfirmationrequirementsoutlinedintheNPRM.OperatorswereaskedtoconductasystemanalysistodeterminetheamountofmileagethatwouldrequireMAOPreconfirmationandthemethodtheywouldusetoperformthework.OperatorsprovidedmileageestimatesforbothpipelinesectionsrequiringMAOPreconfirmation,andalsovalve-to-valvespacingthatwouldimpacttotalblowdownmileage.Over100,000milesofinterstateandintrastatemileswereassessedfromanumberofdiversesystems.Systemswereuniqueintermsofgeographiclocations,sizesandpressures,andrepresentroughly44percentofallinterstate

10CommentsoftheInterstateNaturalGasAssociationofAmericaregarding“PipelineSafety:SafetyofGasTransmissionandGatheringPipelines(DocketID:PHMSA-2011-0023),http://www.ingaa.org/File.aspx?id=29912&v=ccaef774(July7,2016).11CommentsoftheAmericanGasAssociationontheSafetyofGasTransmissionandGatheringPipelinesProposedRule,https://www.aga.org/sites/default/files/aga_comments_-_gas_transmission_gathering_lines_nprm_-_july_2016.pdf(July2016).12Id.


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andintrastatemileage.13RespondentsvoluntarilyparticipatedintheanalysisbypullingdatafromatleastoneoftheirpipelinesystemsandestimatingtheamountofmileagethatwouldbeimpactedbyMAOPreconfirmationrequirementsintheNPRM.Operatorswerethenpromptedtoestimatethepercentoftheblowdownmileagewhereamitigationtechniquecouldbeappliedandtherelativecostofthemitigation.Datawascollectedandmodeledtoreflectrangesfromoperatorinput,andfinallyextrapolatedfortheentireindustry.P-PIC’sanalysisaimstoestimatethetotalvolumeofgasreleasesassociatedwiththeMAOPreconfirmationrequirementsintheNPRMascurrentlyproposed.Tocreatethemodel,thefollowingstepswereusedtoestimatetheblowdownmileageandassociatedgasreleases:

1. EstimatethemileageofpipesegmentsrequiredtoreconfirmMAOP,includingconsiderationsforvalvespacing

2. Estimatethetotalvolumegasreleasesfromblowdowns,usingoperatorpressureanddiameterdata

3. Estimatethemileageforwhicheachmitigationoptioncouldbeused

1.4RecalculatingBlowdownMileageEstimateMileageisanimportantcomponentincalculatingthetotalvolumeofgasreleasesassociatedwiththerequirementtoreconfirmMAOP.AsshowinTable1,Table2andTable3,therearedifferentnumbersreportedinthePRIA,intheM.J.Bradleyreport,andbyindustry.ThissectiondiscussesthevariousmileageestimatesandP-PIC’sapproachtoaccountingforthesectionofpipethatmustbeisolatedduringpressuretesting.PHMSABlowdownMileageEstimatesPHMSAcalculatesmileageusingthe2014PHMSAAnnualReportdataandinaddition,usescertainassumptions,suchastheestimatedpercentofMCAmileageassumedtobepiggable,todeterminethetotalMAOPreconfirmationmileage.P-PICassumesPHMSA’smileagecalculationsareanaccuraterepresentationofindustrytransmissionmileage.Table1reflectsmileageoutlinedinthePRIAinTopicArea1.

13TotalInterstatemileageisbasedon2014PHMSAdataasreportedinthePRIAinTable3-1:OnshoreGasTransmissionMileagebyPercentSMYS,foundonpage33.Totalmileageisreportedas278,003totalinterstateandintrastatemiles.


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Table1:PHMSAMAOPReconfirmationMileageReportedinRIALocation Untested

HCA>30%SMYSMileage1

InadequateRecordsMileage2

UntestedHCAOperatingat20-30%SYMS3

UntestedClass3,Class4HCA3

MCAMileageClass1andClass23

InterstateClass1 59 79 3 0 630Class2 19 97 2 0 538Class3 357 1,109 41 888 0Class4 0 1 0 0 0IntrastateClass1 10 32 1 0 78Class2 13 34 4 0 147Class3 451 2,886 213 724 0Class4 3 126 3 1 0Subtotal 912 4,364 267 1,613 1,393Source:PHMSA2014AnnualReportdata.Reportablein-serviceincidentsincelastsubpartJpressuretestdatawasnotincludedintheRIA.

PHMSAseparatelycalculatedthemilesthatwouldrequireablowdownduetopressuretestsandILIupgrade.TheresultoftheestimationiscontainedinTable3-50inthePRIAandequatesto3,146milesofblowdown.NotethatPHMSAestimatesthatallMCAmileagewouldrequireanILIasopposedtopressuretest.Inaddition,PHMSA’scalculationsubtractsmileagefromcompliancewithMAOPreconfirmationrequirementsfromHCApressuretestmiles.

Table2:PHMSAPressureTestandILIUpgradeMileageReportedinRIALocation Untested

HCA>30%SMYSMileage1


UntestedHCAOperatingat20-30%SYMS3


MCAMileageClass1andClass23

InterstatePressureTest 2 36 59 36 0ILIUpgrade 23 267 0 259 0IntrastatePressureTest 47 566 191 109 0ILIUpgrade 118 1,174 0 259 0Subtotal 190 2,043 250 663 0Source:PHMSAdatacontainedonpage64andpage65oftheRIA.

M.J.BradleyBlowdownMileageEstimateM.JBradleycitesPHMSA’sPRIAasthebasisfortheirestimated3,509totalmilesofblowdown.ThetotalmileagedoesnotbackoutthecurrentcompliancerequirementstocompleteintegritymanagementassessmentsinHCAsegmentsunderSubpartOofthePipelineSafetyRegulations.Assuch,theM.J.Bradley


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estimateisslightlyhigherthanPHMSA’stotalpressuretestandILIupgrademileage.

Table3:M.J.BradleyMileageUsedInReport

Location TotalMileageInterstate 776Intrastate 2,733Subtotal 3,509Source:M.J.BradleyReportpage12.

P-PICBlowdownMileageEstimateP-PIC’sblowdowncalculationsusethetotalmileagereflectedinTable1,withtheadditionofreportablein-serviceincidentmileagesincelastpressuretest,whichaddsanadditional468milesofblowdown.ThisadditionalmileagewasnotincludedinthePRIA,butwouldberequiredtoundergoMAOPreconfirmation,pertheNPRM.

Table4:P-PICMileageToReconfirmMAOPWithoutValve-to-ValveSpacingLocation Untested

HCA>30%SMYS

Mileage1


UntestedHCA

Operatingat20-30%SYMS3


MCAMileageClass1

andClass23

ReportableIn-Service

IncidentsincelastPressure

TestInterstate Class1 59 79 3 0 630 354Class2 19 97 2 0 538Class3 357 1,109 41 888 0 Class4 0 1 0 0 0 Intrastate Class1 10 32 1 0 78 114Class2 13 34 4 0 147Class3 451 2,886 213 724 0 Class4 3 126 3 1 0 Subtotal 912 4,364 267 1,613 1,393 468Source:PHMSA2014AnnualReportdata.Reportablein-serviceincidentsincelastsubpartJpressuretestdatawasnotincludedintheRIA.Mileagebasedonindustrydata.P-PICassumesthatallmileagerequiringMAOPreconfirmationwillbepressuretestedasopposedtoanyothertypeofassessmentapproach,basedonindustrycommentsregardingtheimpracticablenatureoftheECAapproachasproposedintheNPRM.14,15EveniftheproposedECAapproachcanbeusedtoreconfirm

14CommentsoftheInterstateNaturalGasAssociationofAmericaregarding“PipelineSafety:SafetyofGasTransmissionandGatheringPipelines(DocketID:PHMSA-2011-0023),http://www.ingaa.org/File.aspx?id=29912&v=ccaef774(July7,2016).15CommentsoftheAmericanGasAssociationontheSafetyofGasTransmissionandGatheringPipelinesProposedRule,https://www.aga.org/sites/default/files/aga_comments_-_gas_transmission_gathering_lines_nprm_-_july_2016.pdf(July2016).


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MAOPinselectcases,P-PIC’sgasreleaseestimatesserveasabookendforthepotentialimpactsoftheproposedMAOPreconfirmationrequirements.Thus,summingthesubtotalsinTable4,thetotalblowdownmileageduetoMAOPreconfirmationusedinP-PIC’sanalysisis9,017milesofpipeline.Thisissubstantiallylargerthanthe3,148milesoutlinedinPHMSA’sPRIAorthe3,509milesoutlinedintheM.J.Bradleystudy,andreflectsoperatorfeedbackthatpressuretestingforMAOPreconfirmationwillgenerallyoccurseparatelyfromintegritymanagementprogramassessments,asdiscussedabove.Itisalsocriticaltoconsidertheimpactofvalve-to-valvespacingonthetotalmileagethatwouldbeblowndownforMAOPreconfirmation.Usingonlythetotalmileageforcalculatingthevolumeofgasreleasesunderestimatesthetotalimpact.Typically,whenconductingahydrotest,operatorswillneedtoblowdownthecompletesegmentbetweentwovalves,evenifonlyashortsectionwithinthesegmentrequiresMAOPreconfirmation.AnalysisofparticipatingoperatordatademonstratesthatforeverymileofpipelinerequiringMAOPreconfirmation,4to6milesofpipelinewillneedtobeblowndowntoaccommodateahydrotest,eventhoughMAOPreconfirmationisnotrequiredonthisextramileage16.Table5recalculatestotalblowdownmileagebasedonthesechangesandgivesamorerealisticviewoftheamountofpipelinemileagethatwillbeimpactedbytheMAOPreconfirmationrequirementsintheNPRM.P-PICestimatesanaverageoffivepipelinemilesmustbeblowndownforevery1mileofpipelinerequiringMAOPreconfirmation,basedonthe4-6milerangeindicatedbyoperatordata.

Table5:P-PICTotalBlowdownWithValve-to-ValveSpacingMileage IndustryPT

MileageEstimate

withoutValvetoValve

IndustryPTMileagewithValvetoValvespacingevery

4miles

IndustryPTMileagewithValvetoValvespacingevery

6miles

AveragePTMileagewithValve-ToValveSpacing

Interstate 4,177 16,708 25,062 20,885Intrastate 4,840 19,360 29,040 24,200Totals 9,017 36,068 54,102 45,085Source:Industrysystemdata

1.5EstimateofTotalGasReleaseWithoutMitigationThetotalvolumeofgasreleasesisdependentonseveralfactors,includingpipelinediameter,pressure,temperature,andotherfactors.Gasreleasesareassociatedwithnormalmaintenanceoperations,includingblowdownsrelatedtopressuretestsandupgradingpipelinefacilities,inadditiontoothergas-operatedpneumatic

16Basedonoperatorsystemdataanalysis.


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devicesthatsometimesreleasegas.However,thegasreleaseestimatesinP-PIC’sanalysisonlyapplytoblowdownsassociatedwiththespecificrequirementsforMAOPreconfirmationoutlinedintheNPRM.AsitrelatestoMAOPreconfirmation,themileagereportedinTable5wouldresultinasubstantialvolumeofgasreleases.Themajorityofnaturalgasiscomposedofmethane(95.7percent),whilecarbonaccountsfor1.3percentandtheremainderisothertypesoffluidequals3.0percent17.GasreleasesarecalculatedonapermilebasisandtakeintoconsiderationpipelinediameterasproposedbyM.J.Bradleyandaveragesofoperatingpressuredataprovidedbyparticipatingoperators.Forsimplicitypurposes,thisanalysisdoesnottakeintoaccounttheaverageblowdownlength,whichtheM.J.Bradleyreportestimatesat15miles,onaverage,andoperatorsestimatebetween10-22miles.PipelineDiameterEstimateM.J.BradleyaggregatedpipelineoperatordataannuallysubmittedtoPHMSAtocalculatetheweightedaveragepipelinediameterforinterstateandintrastatepipelines.Thedatawasorganizedintothreecategories:lessthan12inch,12-34inchesandgreaterthan34inches.Thefollowingtableisare-creationofTable2intheM.J.Bradleyreport.Thepercentageofpipelinemileageisbasedonthe2014annualreportpresentedinPHMSA’sPRIA.TotalaveragemileagefromTable2aboveismultipliedbythepercentageofweighteddiameterstoestimateblowdownmileageforeachdiameterrange.

Table6:PHMSAWeightedAveragePipeDiameter(inches)SizeBin WTDAvg.

Diameter1%OfPipelineMileage2

BlowdownMileage3

Interstate<12inches 8.0 27% 5,639

12-34inches 24.3 57% 11,904>34inches 37.8 16% 3,342

Totals 22.0 - 20,885Intrastate

<12inches 8.2 56% 13,55212-34inches 21.7 37% 8,954>34inches 38.7 7% 1,694

Totals 15.0 - 24,2001.Foranalysispurposes,thisreportusesthePHMSAandM.J.BradleyaveragediametersfromTable2:WeightedAveragePipeDiameter(inches),TransmissionPipelines(page10ofthereport).2.Basedon2014AnnualReportdataforGasTransmissionoutlinedinthePRIATable

17Seetable3-46intheRIA.SourceiscitedbasedonEnbridgeandSpectraestimatesandreflectsthepercentvolumeofthecompositionofnaturalgas.


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3-47:ProportionofGasTransmissionMileagebyDiameter(page63ofthePRIA).3.BlowdownmileageiscalculatedbyusingaveragemileageestimatesfromTable2ofthisreportmultipliedbythepercentageofpipelinediameter.

PipelinePressureEstimateOneofthekeyassumptionsinthePHMSAPRIAisthattheaverageoperatingpressureofpipelinesystemsisapproximately400psi.Thisisaninaccurateandunsubstantiatedassumptionthatimpactsthegasreleasecalculationsignificantly,especiallyasitrelatestointerstatepipelines.TheM.J.Bradleyreportsaddressesthisaspect(startingonpage10),butM.J.Bradleydoesnotdetermineamoreappropriateaveragepressure,duetoalackofindependentdata.Operatorswereaskedtoanalyzetheirsystemandreportonthepressures.Similartothemethodforestimatingdiameter,pressureshavebeengroupedintothreecategoriestoarriveatanaveragepressure.

Table7:P-PICEstimatedWeightedAveragePipelinePressure(psi)SizeBin WTDAvg.

Pressure(PSI)

%OfPipelineMileage2

WeightedAverage(PSI)

Interstate<500 409 1% 4.09

500-1,000 680 85% 578>1,000 1,234 14% 172.76Totals - - 754.85

Intrastate<500 200 36% 71

500-1,000 750 61% 456>1,000 1020 3% 31Totals - - 558

Source:OperatorsystemdataprovidedtoINGAA

1.6EstimatedTotalGasandMethaneReleaseCalculationsTocalculatethetotalvolumeofgasreleasesduringblowdowns,thePHMSAPRIAusedthefollowingequation(page37ofthePRIA):

GasReleased(Vb)=(28.798x(Tb/Pb))x(Pavg/(ZavgxTavg))xD2)/100

Vb=Volumeofgasreleasedpermile(Mcf)Tb=Temperatureatstandardconditions(70°F)Pb=Pressureatstandardconditions(14.7psi)Pavg=PressureatblowdownconditionsZavg=Compressibilityfactoratpackedconditions(0.88)Tavg=Temperatureatpackedconditions(70°F)


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D=Insidediameterofpipelineininches

TheM.J.BradleyreportaddressesinaccuracyinthegascompressibilityfactorreportedinthePHMSAPRIA,whichusesavalueof0.88,whichdoesnotcorrectlycorrespondtoa400psipressure.M.J.Bradleyusesavalueof0.926,whichmorecorrectlyreflectsthepressureof400psig.However,a400psigagaindoesnotaccuratelyreflecttheaveragepressuresupportedthroughoutpipelinesystems.Inaddition,M.J.Bradleycorrectlyusesanabsolutescaleforthetemperaturevaluesintheequation(Kelvin),whichwasundefinedinthePHMSAPRIA.P-PICconferredwithanumberofsourcesanddeterminedthatthegascompressibilityfactorshouldbecalculatedusingthePengandRobinsonequationofstate,whichisconsistentwiththecompressibilityfactorintheM.J.Bradleyreport.18P-PICusedthePHMSAequationwithacorrectedcompressibilityfactor,temperaturescaleanddiameter.P-PICuseddegreesRankineinsteadofKelvinfortemperature,anabsolutepressureinsteadofgaugepressure,andacompressibilityfactorfromthesamesourceasM.J.Bradley.P-PICoptedtoalignwiththeM.J.Bradleycalculationforconsistencywhencomparingtotalgasreleaseestimates.

GasReleased(Vb)=(28.798x(Tb/Pb))x(Pavg/(ZavgxTavg))xD2)/100

Vb=Volumeofgasreleasedpermile(Mcf)Tb=Temperatureatstandardconditions(520°R)Pb=Pressureatstandardconditions(14.7psi)Pavg=PressureatblowdownconditionsZavg=Compressibilityfactoratpackedconditions(0.88)Tavg=Temperatureatpackedconditions(530°R)D=Insidediameterofpipelineininches

Table 8 below summarizes P-PIC’s blowdown gas release calculations, based onthemileage,diameter,andpressureestimatesdiscussedaboveforpipelinesthatwouldbe required toundergoMAOP reconfirmationper theNPRM. Blowdownmitigation options are addressed later in this report, so Table 8 assumes noblowdownmitigationsareemployed.

18BlueSourceCanada,BlowdownProtocolforPipelineSystems,AppendixAGASDEVIATIONFACTORQUANTIFICATION,April2011.http://pacificcarbontrust.com/assets/Uploads/Protocols/Blowdown-ProtocolApr-14.pdf.


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Table8:P-PICEstimatedTotalGasRelease

SizeBin 12” 14-34” 36”+Interstate

Weighted1 27% 57% 16%Mileage 5639 11,904 3,342

GasReleaseperMile2 207 886 2,035TotalGasRelease(MCF,15Yr3) 1,169,107 10,541,595 6,801,799

MethaneRelease(MCF,15Yr4) 1,118,836 10,088,306 6,801,799MethaneRelease(MCFperYear) 74,589 672,554 453,453

IntrastateWeighted1 57% 37% 7%

Mileage 13,794 8,954 1,694GasReleaseperMile2(MCF) 154 659 1,514

TotalGasRelease(MCF,15Yr3) 2,127,743 5,899,117 2,565,403TotalMethane(MCF,15Yr4) 2,036,250 5,645,455 2,455,091

MethaneReleaseperYear(MCF) 135,750 376,364 163,6731.BasedonpercentagescontainedinthePHMSAPRIA2.BasedonpressurefromTable6anddiameterscontainedinthePRIAandroundedpressureof750psi,usingequationcontainedinthePHMSAPRIAwithmodificationsoftemperatureandzfactor.Exampleequationfor12”interstate:=28.798*(520/14.7)*(750/(0.88*530))*(11.25)2/10003.Gasreleasedpermilemultipliedbymileage4.Gasreleasedmultipliedbymileageby.957

1.7ComparisonofMethaneReleaseCalculationsTable9belowcomparestheP-PIC,M.J.Bradley,andPHMSAmethanereleaseimpactsoftheMAOPreconfirmationrequirementsintheNPRM.PerthePHMSAPRIA,theMAOPreconfirmationrequirementswouldresultin975,180MCFofmethanereleases,duetopressuretestsandILIupgrade.Asreviewedabove,P-PIC’smethaneestimatesarelargerduetooperatordataevidencingthathigheraveragesystemoperatingpressureandlargeramountsofblowdownmileageshouldbereflectedinthecalculation.Similarly,M.J.Bradleywasunabletore-calculatemileageand,therefore,thevolumeofmethanereleasesestimatedintheM.J.BradleyreportarelowerthanP-PIC’sestimates.

Table9:EstimatedMethaneReleaseComparisonOver15YearsMileage TotalMethane(MCF) TotalMethane

(Tonnes)P-PIC 28,145,736 538,445PHMSA 975,1801 18,656M.J.Bradley 1,060,6572 20,2911.MethaneEmissionscontainedinPRIA,Table3-54TotalGHGEmissionsduetoBlowdowns(page65).2.Basedon20,291MetricTonsofMethanereportedintheM.J.


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BradleyReport(page13).MetrictonsconvertedtoMCF.

P-PICestimatesthat28billioncubicfeetofmethanemaybereleasedasaresultoftheMAOPreconfirmationrequirementsintheNPRM,whichis25timesmorethantheM.J.BradleyandPHMSAestimate.Thisassumesnoblowdownmitigationstechniquesareemployed.

2.0InterstateMitigationOptionAnalysisTheM.J.Bradleyreportdescribesavarietyofmitigationmethodstoreducegasreleases:gasflaring,pressurereductionusingin-lineorportablecompressors,gasinjectiontoanear-bylow-pressureline,andapplyingstopples.Detailsabouteachmethodarehighlightedstartinginsection2.1ofthisreport.Surveyinginterstatetransmissionpipelineoperators,themajorityofplannedmaintenanceblowdowns,includinghydrotestsforMAOPreconfirmation,canandoftendoutilizeoneofthefivemitigationoptionoutlinedintheM.J.Bradleyreport,ifoperationallyandeconomicallyfeasible.Mitigationoptionsarenotonlybeneficialfromanenvironmentalperspective,butastheM.J.Bradleyreporthighlights,thereisaneconomicincentiveforoperatorstomitigatewhenappropriate.However,thereareimportantconsiderationsthatmustbetakenintoaccountwithrespecttomitigation.Systemtypeisanimportantfactor,andthereareinherentdifferencesbetweeninterstateandintrastatepipelines,whichimpactthefeasibilityofcertainmitigationoptions.ThescenariosbelowreflectafutureestimatefortheusageofmitigationoptionsfortheblowdownsassociatedwiththeMAOPreconfirmationrequirementsintheNPRM.ThisanalysisisapplicableonlytoblowdownsassociatedwithscheduledhydrotestworkforMAOPreconfirmation.Whenmaintenanceworkcannotbeplannedfarinadvance(e.g.immediaterepairconditions),equipmentavailability,customerreliabilityimpacts,andotherlimitationsmaysignificantlyrestrictthemitigationmethodsthatcouldpracticablybeemployed.Theanalysisisderivedfromasubsetofoperatorsassessingthepossibilityofusingspecificmitigationtechniquesbasedonanumberofsystemfactors.However,itisimportanttokeepinmindthatthevarietyofsystemsandsystemcharacteristicsmakeitdifficulttoapplyaccurateusageestimatesformitigationalternativesthatrepresenttheentireindustry.Table10outlinestheamountofinterstatemileageassumedtobeloopedversusasinglebarrelsystem;thesesystemdifferencesimpactthelikelihoodthatcertainblowdownmitigationoptionscanbepracticablyemployed.Aloopedsystemiswhentwoormorepipelinesarelaidinparalleltoincreasecapacityalongaright-


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of-way,bothendsconnecttotheoriginalpipeline.Inthesesystems,low-pressurediversionismuchmorecommonasamitigationoptionbecausetherearemultiplelinesavailableintheright-of-way.Atthesametime,in-linecompressionmayprovidelimitedbenefitasamitigationoptionforloopedsystems,becausetheotherlinesintheright-of-wayarerelyingonthecompressiontomaintainaconsistentlinepressure.Asinglebarrelsystemisasinglepipelinebetweentheoriginanddestination.Thesearetypicallylargerindiameter,long-haul,trunklinesystemsthattendtohavefewerreceiptanddeliverypoints.Thesesystemshavefewerlow-pressurediversionoptions,bututilizingin-linecompressiontoreducepipelinepressurepriortoblowdownmaybemorefeasibleprovidedtheinterruptionofservicecanbeaccommodated.P-PICsegmentedtheamountofloopedandsinglebarrelsystemmileagebasedonindustrydata.Fromthere,certainassumptionswereusedtoreflecttheamountoftimemitigationoptionscouldbeutilized.AsshowninTable10below,theseutilizationestimatesforeachmitigationoptionandnon-mitigationaremultipliedbymileagepersystemtypetogenerateamileageestimateforwhicheachofthemitigationoptionscanbeutilized.

Table10:P-PICEstimatedMileageforMitigationOptions(Interstate)

Mileage

Avg.EstimatedLoopedSystem

MitigationOptionUtilization

Avg.EstimatedSingleBarrel

SystemMitigationOptionUtilization

EstimatedLoopedSystemMitigationOptionUtilization,

byMile

EstimatedSingleBarrelSystem

MitigationOptionUtilization,byMile

TotalMitigationOptionUtilization,

byMile

%ofMileage 70% 30% 14,620 6,266 20,885

12”Weighted 15% 30% 3,133 1,880

14-34” 70% 60% 14,620 12,531

36”+ 15% 10% 3133 2,089

Flaring 2.50% 2.50% 365 157 522In-LineCompressionandMobileCompression

60% 70% 8772 4386 13,158

LowPressureDiversion

15% 5% 2193 313 2,506

Stopples 2.50% 2.50% 365 157 522

NoMitigationOptionAvailable

20% 20% 2924 1253 4,177

TOTAL 100% 100% 14,620 6,266 20,8851.Basedon2.5%Source:Operatorsystemdata.,whichrepresentsover100,000milesofinterstatemileage.

AsexplainedintheM.J.Bradleyreport,eachmitigationoptionhaslimitstothegaspressurereductionachievablepriortoblowdown.Insomecases,operatordatasuggestsmorereductionthanreportedbyM.J.Bradley.Inothercases,theremay


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beless.Table11outlinesthepressurereductionsbymitigationoptionbasedonindustryfeedback.InTable11,aninitialpressureof750psi(rounded,perTable4)wasmultipliedbytheblowdownreductionpercentagetoarriveatafinalpressure.Gasreleasecalculationstakeintoaccountthe22.0-inchdiameterforinterstatepipelinesusedbyPHMSAandM.J.Bradley,aswellasthecompressibilityandtemperaturefactorsdiscussedabove.

Table11:P-PICEstimatedGasReleasedwithMitigation(Interstate)

Mileage BlowdownReduction

MilesofInterstatePipeline

InitialPressure(psi)

FinalBlowdownPressure(psi)

GasReleasedPerMile(Mcf)1

TotalGasReleasedover15Years(Mcf)

TotalMethaneReleasedover15Years(Mcf)

Flaring2 95% 522 750 37.5 138 20,487 19,606In-Line

CompressionwithMobileCompression

80-90% 13,220 750 112.5 418 1,556,622 1,489,688

LowPressureDiversion

25% 2,444 750 562.5 2,176 1,544,984 1,478,688

Stopples 75% 522 750 187.5 700 103,580 99,126No

MitigationOptionAvailable

0% 4,177 750 750 3,128 3,702,500 3,543,293

TOTAL - 20,885 - - 6,928,173 6,630,2611.Basedon22.0IDandZfactorbasedonfinalkPA2.FlaringemitsCO2fromcombustion,buthasnotbeenaccountedforinP-PIC’sestimateSource:Operatorsystemdata

Table12:P-PICEstimatedTotalVolumeofMethaneReleasesfrom

ReconfirmingMAOPTotalVolumeofMethaneReleases

withoutMitigation(MCF)1TotalVolumeofMethane

ReleaseswithMitigation(MCF)18,008,940 6,630,261

1.TotalInterstatemethanereleasesover15yearsfromTable8(1,118,326+10,088,306+6,801,799=18,008,940)2.FromTable11.

Thefollowingsectionsreviewthevariousmitigationoptionsandoperatorfeedbackoneachoptioninfurtherdetail.


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2.1FlaringFlaringistheprocessofrecoveringnaturalgasthatwouldtypicallybeblowndowntotheatmosphereandinsteadiscombustedinaflare.Accordingtoserviceproviders,usingflaresmayresultinapressurereductiondownto0psi,resultingina95%to100%pressurereduction.However,CO2isthepredominantcombustion-relatedemission.AccordingtoM.J.Bradley,theCO2producedduringthisprocessequatesto2.75metrictonsofcarbonperonemetrictonofmethane.Accordingtooperators,flaringtomitigatepipelineblowdownvolumesisutilizedrarely–onlyfor1-5%ofblowdowns.Stateairqualityregulationsandpermitrequirementslimittheuseofflaring.Thetimedurationrequiredtoreducelinepressurethroughflaringisalsoaconcern;dependingontheonthesizeoftheflare,thiscanrangefrom8to18hours.Largerflaresburngasfasterandminimizethetimedurationforablowdownoperation;however,theseflaresrequiremoremanpower,setupandadditionalequipment,whichraisetheoverallcostoftheblowdown.Safetyisacriticalconcern,andflaresizeandutilizationtomitigateblowdownsarelimitedbytheheataffectedzone.Thepublicmayalsoconsiderflaringtobeavisualnuisance.

2.1.1EnvironmentalPermitsWhileaportableflarewillreducethevolumeofnaturalgasreleasestotheatmosphere,itwillresultinreleasingadditionalcompounds,likeCO,NOx,andCO2,thatwouldnothavebeenreleasedfromanon-flaredgasrelease.Stateairqualityregulationsrequireoperatorstosubmitanotification,obtainanairpermitorairauthorizationforusingaportableflarealongthepipeline.Airqualitypermittingtimeframesmaylimitthefeasibilityofusingaflare,andinsomelocations(e.g.,nonattainmentareas)flaringforblowdownmitigationmaynotbeallowedatall.

2.1.2 HeatAffectedZoneTemporaryorpermanentflaresarerequiredtobeinstalledinlocationsawayfromgassources,flammablematerials,overheadlines,homes,andanyotherplacesthatposeproblems.Theareaoutsideoftheselocationsisknownastheheataffectedzone,anareawherethethermalradiationemittedfromtheflareswouldbedetrimental.Thelevelsofthermalradiationthatcouldbeemittedfromaflareisdependentonanumberoffactorsincludinggascomposition,airdispersion,wind,flaredesign(type,burnerdesign,flametemperatureandheight).Insomecases,dependingontheheightoftheflare,guywiresarerequiredtosupporttheflare.Thesefactorsmaylimitthesizeorutilizationofflaringasamitigationoptionforpipelineblowdowns.


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2.1.3 PublicConcernsFlaringmayattractpublicconcern,basedonthecombustionandburningofnaturalgas,fromhomeownersandlandownersthatliveincloseproximitytoflaring.Membersofthepublicmayconsiderflaringtocreateavisualdisturbance.

2.2PressureReductionwithIn-LineCompressorsInsomecases,existingin-linecompressioncanbeusedtoreducetheoperatingpressurepriortoblowdown,whichwouldultimatelyreducethevolumeofgasreleasedduringtheblowdown.This“drawdown”methodcanbeapracticaloptionforoperatorsduetotheabilitytoutilizeexistinginfrastructureandincurringminimalcostsforlaborandengineeringanalysis.Thatbeingsaid,operatorsneedtoassessthefeasibilityofthepressurereductionandimpactoncustomerdeliveries.Operatorsmustevaluatetheoriginalengineeringdesigntodeterminecompressordischargetemperaturelimitsandminimumdeliverypressurerequirementspriortodrawdown.Stationarycompressionequipmentisdesignedtooperatewithinaspecificpressureandflowrange,whichvariesbyequipmenttype.Manyfactorsareconsideredwhenselectingcompression,suchascontrols,numberofcompressors,boresize,staging,impellerdiameterandmass.Operatingoutsideofthespecifiedrangeofthisequipmentcanriskmechanicalfailureorcomplianceexceedances.Asdrawdownsoccurandcompressionratiosincrease,compressordischargetemperaturesincrease,andoperatingacompressor/pipelineabovetemperaturedesignlimitscancausedamagetothepipelinesystem.Anengineeringanalysisisneededtoevaluatetheeffectoftemperaturechangesontheoutsidecoatingandcathodicprotectiononthepipeline.Inaddition,asthepressureratioincreasesacrossthecompressor,sodoestheriskofdamagingcompressorcomponents,suchasthecompressorvalves,compressorrods,andbearing.Thereisriskofafailureofanin-linereciprocatingcompressorunitifsuctiondropstoolowresultingintheunitunloadingandincompletecombustion.Thesameappliesforcentrifugalunits.Thislimitsthepressurereductionachievablepriortoblowdown,asunitswillautomaticallyshutdownwhentheheadpressuredropsbelowthesuctionpressureminimumsetpoint.Reciprocatingcompressionenginesofferbenefitsfordrawdownsbecausetheyprovidethemostflexibilityforreducingpipelinepressure.Reciprocatingcompressorsaremoreeffectiveandflexible,withindesignlimits,indrawingdownapipelinesegment.Reciprocatingcompressorsusedinmainlinetransmissionservicearedesignedforhighthroughputlowdifferentialapplications.Reciprocatingengineswithpollutioncontrolsarebettersuitedfordrawdowns


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sincetheycancontrolA/Fratio,speed,load,temperatureandexhaust.Thatsaid,compressorrodloadlimitsrestrictthepressurereductionthatcanbeachievedutilizingin-linecompression,andairqualitypermitsmaynotallowthesecontrolstobechanged.Asthedifferentialbetweensuctionanddischargepressuresincreases,thecompressorrodloadlimitwilleventuallybereached,generallyresultinginashutdownofthecompressor.Turbine-andelectric-drivencentrifugalcompressorsmayhavelimitedeffectivenessindrawingdownlines,becausecentrifugalcompressorshaveamorenarrowoperatingrangethanreciprocatingcompressors.Asthesuctionpressuredropsduringapulldown,theflowacrossthecompressoralsodecreases.Whenthisoccursoncentrifugalcompressorswithautomaticrecyclecapability,therecyclevalveopensrenderingthedrawdownineffective.Forcentrifugalcompressorsthatdonothaverecyclecapability,thereducedflowpushesthecompressortowarditssurgeline,andtheunitcontrolstaketheunitoff-linetoprotectitself.Thedistancefromtheblowdownsitestothecompressorstationisanimportantfactor.Incertainsituations,thehydrotestsegmentcouldbe50to60milesupstreamofthecompressorstation,andthismaylimitthepressurereductionthatcanbeachievedpriortoblowdownatthehydrotestsegmentBasedontheseconsiderations,pressurereductionusingstationarycompressionpriortoblowdownisnotpracticalforeveryblowdownscenario.Accordingtointerstatepipelineoperators,theyarelikelytousethisreductionoption60-70percentofthetime,whereasintrastatesystemsarelesslikelytousethistypeoftechnology.Thisdisparityisduetothenatureofintrastatepipelines,whereoutagesoftenhaveamoredirectimpactongascustomers.Thiscreatesanurgencyforintrastateoperatorstoreturnthepipelinetoservicequickly,soitmaynotbefeasibletowaitforin-linecompressiontoreducepressurepriortostartingahydrotest.OperatorsagreewiththeM.J.Bradleyreportthattheestimatedpressurereductionthatcanbeachievedusingin-linecompressionisapproximately50percent.Combiningin-linecompressionwithmobilecompression,operatorswillseeagreatergasreleasereductionofapproximately80-90percent.

2.3PressureReductionwithMobileCompressorsMobilecompressioncanbeusedtograduallyreducepipelinepressurepriortoblowdown,andultimatelyreducethevolumeofgasreleasedduringtheblowdown.Themajorityofoperatorsusethird-partyserviceprovidersforsupplyingmobilecompressionrentals,andmobilizationofthisequipmentcantake


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twoweekstoschedule,ataminimum.MobilecompressorsarecapableofdrawingtheaffectedpipelinedownfromMAOPtoapproximately50psig.However,becausetheseunitsaresmall,thedrawdowndurationofapipelinesegmentwithasinglemobilecompressorcantakeseveraldays.Utilizingseveralmobilepulldownunitsinparallel,atahighercost,canreducethedrawdownduration.Siting,stagingandpermittingmobilecompressionunitscanpresentsignificantchallenges,especiallyinmorepopulatedareas.Noise,physicalfootprint,engineemissions,andotherfactorsmaylimitthefeasibilityofutilizingmobilecompression.Thepercentoftimemobilecompressorsareusedbyoperatorsisverydependentonthesystem.Inaddition,thecostofeitherrentingorpurchasingmobilecompressioncanbeveryexpensive.Thesesmallermobilecompressorsaresizedandstagedfordrawdownapplications.Thenumberofmobilecompressorunitswillimpactthescheduleandoverallcostofthepulldownoperation.Forpurposesofthisreport,operatorssuggestedthatutilizingin-linecompressionwithmobilecompressionrepresentsthemosteffectiveandmostoftenemployedstrategyforreducingthevolumeofgasreleasesduetoMAOPreconfirmationblowdowns

2.4LowPressureDiversionLowpressurediversioninvolvestransferringgasfromthepipelinesegmentthatwillbeblowndownintoanothernearbyline,whichmustbeatalowerpressureinordertomovethegas.Asdiscussedpreviously,duetolimitationsinnearbytransmissionpipelines,transferringgastoothersystemsisoftenunavailable.Accordingtomostoperators,diversionisavailableforonly15%ofblowdownsoninterstatesystems.Lowpressurediversionisamorefeasibleoptionforintrastatesystems,duetotheincreasedprevalenceofnearbylower-pressurelinesonintrastatesystems.Whendiversionisavailable,interstateoperatorstypicallyseeagaspressurereductionof25%.

2.5StopplesWhenonlyashortsectionofpipeneedstoundergoMAOPreconfirmation,shortsectionsbetweenvalvescanbeisolatedusingtemporaryisolationstopples.Thisresultsinareductionofthelengthofpiperequiringablowdownand,asaresult,areductioninthevolumeofgasreleased.Usingstoppleswithatemporarybypasscanprovideoperatorswiththeabilitytoperformavarietyofpipeline


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maintenanceactivities,includingpressuretesting,withoutinterruptionofgasdeliverabilitytodownstreamcustomersonsinglelinesystems.Thereareavarietyofconcernswiththismethod,includingpersonnelsafetywithinstallingthisequipmentonanoperatingpipeline,especiallyathigherpressures.Therearealsotheintegrityrisksthatstopplespresenttoapipeline.Aportionofthestoppleapparatusremainsattachedtoapipelineaftertheworkhasbeencompleted.Thesestoppleattachmentsareknowntoaccumulateliquidsovertimeandnotfeasibletoinspect.Typically,operatorsremovethesestoppleswhenpractical,suchasduringdowntimeforthedownstreamcustomerorLDC.Usingstopplescanbeverycostly.Dependingonthesystemdiameterandstopplesize,stopplescanrangebetween$100,000to$1,000,000.Industryreportsthattheyarelikelytousestopplesonlyonetofivepercentofthetime,withanestimatedpressurereductionof75percent19.

3.ResultsofAnalysisThisstudyconsideredtwoaspectsassociatedwithreconfirmingMAOPusingpressuretests,pertherequirementsofPHMSA’s“SafetyofGasTransmissionandGatheringPipelinesNoticeofProposedRulemaking(NPRM).”ThefirstpartofthestudyfocusedontruingupthevolumeofgasthatcouldbereleasedduringpressuretestingforMAOPreconfirmation.Thesecondpartofthestudywasdedicatedtoevaluatingthemethodsandlikelihoodsbywhichcertainblowdownmitigationoptionsmaybeutilized.Althoughthemitigationmethodsandutilizationbreakdownswillshiftdependingonuniquepipelinesystemcharacteristics,theoveralloutcomesandfeasibilityofthevariousmethodsthroughouttheindustrywerediscussed.InreactiontotheM.J.Bradleyreport,P-PICdeterminesthefollowing:

• Theamountofmileagethatwouldbeimpactedbyvalve-to-valveblowdownsforMAOPreconfirmationresultsinasignificantincreaseinmileageoverM.J.BradleyandPHMSA’sestimates.Underreportingthismileageunderreportsthetotalgasreleaseandmethanereleaseestimates.

• TheamountofmileagethatmaybemitigatedusingthemethodsoutlinedintheM.JBradleyreportmaybeoverreported.Operatorsmaybeabletouseamitigationoptionforthemajorityofprojects,butthatwillneedtobedeterminedonacase-by-casebasis.

19Basedonoperatorsystemdataandreducingtheentirevalvetovalvesection.

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