Effect of lateral impact loads on failure of pressurized pip

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Effectoflateralimpactloadsonfailureofpressurizedpipelinessupportedbyfoundation

CSNg1ÃandWQShen21

JPKennyLtd(formerlyUniversityofPortsmouth),Staines,UK2

DepartmentofMechanicalandDesignEngineering,UniversityofPortsmouth,Portsmouth,UK

Themanuscriptwasreceivedon1March2006andwasacceptedafterrevisionforpublicationon23June2006.DOI:10.1243/0954408JPME97

Abstract:Thedynamicinelasticresponseandfailurepredictionofpipelinesunderlateralmassimpactatthemid-spanpositionarepresentedinthisarticle.Atotalof52impacttestswerecarriedoutonseamlessmildsteelpipeswithdifferentinternalpressurelevelsandfoundationsupports.Criticalinitialimpactenergieswereobtainedforeachgroupofpipespecimenswithdifferentinternalpressurelevelsandfoundationsupports.

Numericalsimulationsoftheexperimentaltestswerecarriedoutusingthree-dimensionaldynamicnon-linear niteelementanalysis,wherebothgeometricalandmaterialnon-linear-itieswereconsidered.Goodagreementswereachievedbetweentheimpacttestsresultsandthenumericalpredictions.

Ithasbeenfoundthatthein uencesoftheinternalpressureandthefoundationonthecriti-calinitialimpactenergyaresigni cant.Thecriticalinitialimpactenergyismuchlesssensitivetointernalpressureforthepipeswithafoundationthanthosewithoutafoundation.Keywords:pipeline,foundation, niteelementanalysis,impact,pressure

1INTRODUCTION

Researchonpipelineshasbeencarriedoutforafewdecades.Muchworkhasrecentlybeendoneinanefforttorationalizethedesignofpipelines.Theimpactresponseofsteelpipelinessubjectedtoimpactloadinghasbeenstudiedinmanyarticles[1–8].

Leisetal.[1]showedtheirworksofquantifyingtheeffectsofdentfeatureson awinitiationandgrowthinhigh-pressurepipelines.Itwasreportedthatthefourfactorsthathaveastrongin uenceontheseve-rityofthemechanicaldamageofthepipelinesaresoilsupport,linepressurelevel,linetensionorcompression,andthetype,magnitude,andtheorientationoftheimpactload.

Thomasetal.[2]conductedaseriesofexperimen-taltestsonsimplysupportedtubesunderacentralload.Threedifferentmodesofdeformations,i.e.localdeformation,localandglobaldeformations,andstructuralcollapse,havebeenidenti ed.

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Correspondingauthor:JPKennyLtd,ThamesPlaza,Chertsey

Lane,StainesTW183DT,UK.email:ncs1018@http://doc.guandang.net

Jonesetal.[3]successfullyconductedsevenseriesofimpacttestsoncoldworkedseamlessmildsteelpipes,whichhaddifferentspans,outsidediameters,andthicknesses.Thepipespecimensweresubjectedtoanimpactloadingatdifferentlocationswiththeimpactvelocitiesrangingupto14m/s.

Atheoreticalrigid-perfectlyanalysisforpredictingthequasi-staticresponseofpipelinesthatarefullyclampedacrossaspanandsubjectedtoalateralimpactloadinghasbeendevelopedinreference[4].Thistheoreticalpredictionachievedagoodagree-mentwiththeexperimentalresultsinreference[3].JonesandBirch[5]presentedsomeexperimentaldata,whichwererecordedfromtheir54impacttestsonpressurizedandunpressurizedmildsteelpipes.Allthesepipesweresubjectedtoimpactload-ingfromarigidwedge-shapedindenter,whichhada atimpactface.Moreover,thepipeswerefullyclampedacrossaspanandimpactedatthemid-andone-quarter-spanpositions.Theyrevealedtwomajorfailuremodesoccurringatthepipes,i.e.localfailureandglobalfailure.

Morerecently,anexperimentalstudyonthefail-ureoffullyclampedsteelpipeswasreportedin

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194CSNgandWQShen

reference[6].Atotalof226impacttestswereconductedonthedifferentgeometriesandinternalpressurelevelpipespecimens,whichwerefullyclampedatbothendsandimpactedtransverselybywedge-shapedindentersatdifferentpositions.

Athree-dimensionaldynamicnon-linear niteelementanalysis(FEA)waspresentedinreference[7]inordertosimulatetheactualdynamicinelasticresponseofallthepipesthatweresubjectedtoimpactloading,asreportedinreference[6].Agoodagreementwasobtainedbetweenthenumericalpre-dictionsandthecorrespondingexperimentalresultsforboththecriticalinitialimpactenergyandthemaximumpermanenttransversedisplacementswhenfailureoccurred.

Thetheoreticalanalysisinreference[4]hasbeenfurtherdevelopedtopredictthequasi-staticresponseandtheonsetoffailureforboththepress-urizedandunpressurizedpipelines[8].Themaxi-mumstrainfailurecriterion,theeffectofmaterialstrainratesensitivity,andanempiricalformulaforestimatingtheplastichingelengthwereusedintheanalysis.Goodagreementswereachievedbetweenthetheoreticalpredictionsandthecorrespondingexperimentalresultsinreference[6]forboththecriticalinitialimpactenergyandthemaximumpermanenttransversedeformationofthepipe.

Somefoundationspossiblysupportthepipelinesinthepracticalworkingenvironment,e.g.oil-trans-portationpipelineslyingonseabed.Theeffectof

thefoundationonthedynamicresponsesandfailureofpipelineswhensubjectedtoanaccidentimpactmaybesigni cantandhasnotbeeninvestigatedinthepreviouspublishedarticles.Therefore,aseriesofcarefullyinstrumentedtestsandnumericalsimu-lationsonpressurizedandunpressurizedpipessup-portedbydifferentfoundationswereconductedintheDepartmentofMechanicalandDesignEngineer-ingattheUniversityofPortsmouthforpredictingthefailureofpipelinesundersevereimpactloading.

22.1

EXPERIMENTALDETAILS

Testfacilitiesandinstrumentation

Aschematicdiagramoftheconnectionofinstru-mentsandequipmentsforcarryingouttheexper-imentalworkisshowninFig.1.Apairoftimesensorswas xedatthedrophammerrig,wheretheinitialvelocityoftheindenteratthetimeofimpactingonthetopsurfaceofthepipespecimencouldbepredictedandrecordedusingadigitaltimerandaspeciallydesignedelectroniccircuit.ThearrangementfortheunpressurizedtestisshowninFig.2(a).Steelplatessurroundingthepressurizedpipespecimenswereusedinthepress-urizedtest,asshowninFig.2(b),inordertostoppossibledebrisbeingprojectedduringtheimpact

test.

Fig.1Aschematicdiagramshowingtheconnectionofthetestinstrumentsandequipments

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Effectoflateralimpactloads195

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