JournalofVocationalStudiesonAppliedResearch.Vol.1(2)2019:27-30,Ariwibowo,et.al.

27 JournalofVocationalStudiesonAppliedResearch,Vol.1(2),October2019

FailureAnalysisOfWaterPumpShaft

DidikAriwibowo*,SulthonulPutra,SenoDarmanto,JuliMrihardjono,WijiMangestiyono

Mechanical Design Engineering, Industrial Technology Departement Vocational School of Diponegoro University

Jl.Prof.Soedarto,SH.UNDIP,Tembalang,Semarang,50275,Indonesia

e-mail:didik.ariwibowo@live.undip.ac.idAbstract-Awaterpumpshaftforutilitywaterrawmaterialwasfailed.Theshaftwasbrokenintotwoparts.Whileindismantling,thesandwasfoundinchamberbetweenbearingandshaft.Therewasalsoaboltintheimpeller.Accordingtoreports,thepumphasbeenrepairedandsince therewasnoreplacementshaftbut theshaftwasreused inreverseposition.Therewasno inspectionof theshaftwhenitwasdisconnectedbyoperationalreasons.Thefailureanalysisofthebroken-shaftwasperformedtoinvestigatethecauseofthefailure.Twoinspectionandanalysiswereperfomedthosearevisualinspectionandmaterialidentificationandanalysis.Whenmaterialanalysis of the shaft was carried out there was difference between examination and data specification of the shaft.The materialidentificationindicatethatthematerialwasAISISS304whereasspecificationdatastatesSS316.Bothmaterialshavesimilartensilestress,sothedifferencewasnotthecontributorofthefailure.Thepresentofforeignmaterialwasconsiderasthecauseofthefailure.Theforeignmaterialcausedtostuckedonrotationofshaftandincreasingintensileoftheshaftoveritsultimatestrength.Keywords–verticalpump,tensilestress,ultimatestrength,materialidentificationSubmission:November12,2019 Correction:November19,2019 Accepted:November20,2019Doi:http://dx.doi.org/10.14710/jvsar.1.2.2019.27-30[Howtocitethisarticle:Ariwibowo,D.,PutraS.,Darmanto,S.,Mrihardjono.(2019).FaulireAnalysisofWaterPumpShaft.JournalofVocationalStudies

onAppliedResearch,1(2),27-30.doi:http://dx.doi.org/10.14710/jvsar.1.2.2019.27-30]

1.IntroductionWellpumpisusedtopumpgroundwaterthatusedfor

process, boiler feed water, and human consumablewater.Water contains a lot of iron (Fe), Manganese (Mn),and other minerals. The pump has to deliver water withcapacity of 150m3/hr and head about 84meters. By thecharacteristic of water to be delivered and location, avertical centrifugal pump was chosen for thatrequirements.

The vertical pump used at a typical well was designwithstainlesssteelmaterials.TheconstructionofthepumpanddetailsofpumpspecificationcanbeseenatFig.1andTable1,subsequently[1].

OnNovember,thepumpfailed.Aninformationstatedthatthepumpwasstopworking.Afterbeingbroughttotheshop and initial inspection, it was found that pump shaftbroken to near half of the length of the pump shaft, andsome impeller parts were damaged at side of the blade.Further moreforeign particles such as sand and newpebblesandbowlboltscasinginsidethepumpwasfound.

Based on the information, cause effect analysis wascarriedouttoinvestigatefailureoftheshaft.

Figure1.VerticalCentrifugalPump

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Table1.SpecificationofVerticalCentrifugalPump

2.AnalysisProcedureTheproceduretoinvestigatethefailureofpumpshaft

wasperformedinthestepsbelow[2,3]:a. Visualinspectionandexaminationb. MaterialIdentificationVisualinspectionwasperformedbytakingapictureof

thefailurepartofshaftandanalysistheformofthebroken.The geometry and modes of crack were identify andanalyze.IntheMaterialidentificationstep,pumpshaftwasexamine by Olympus Alloy Analyzer that shows thechemical composition of shaft materials. The identifiedmaterialwasusedtoknowitsstrengthofthematerial,thestrengthtowhitstandtensileoccursinshaft.

3.ResultsandDiscussion3.1.VisualInspectionandAnalysis

Visualinspectionwascarriedouttoanalyzethemodesof failure. One of the picture can be seen at Fig.2. Thisleading to hypotheses that shaft failed in torsion loadingcondition.The figure shows that there is a crack initiation.This mode of failure was consider that shaft sustained arotationalloadthatcausethetensilestressoveritsultimatestrength. This initial crack was mis-inspection. Fromhistoricalmaintenancedata, theshaftwasnotchecked forit.

The cause of the over tensile strength was of theforeignmaterial,thosearesandandboltinpumpchamber.Theboltthatfoundinthechamberanddamageofimpellercanbe seenat Fig.4.The rotationof shaftwas stuckedbythebolt,causetensilestressincreasedintheshaftoveritstensile strength. The initial crack extents until shaft

broken.Besides the stucked, imbalance that cause of boltexerted in impeller could also be contributor of shaftfailure. It can also be seen that their direction of initialcrack and failure was different. This is caused bymaintenanceactivitythatchangetheverticalpositionoftheshaft This failure phenomena is similar to that in pumpshaftfailurestudiedbysomeresearcher[2,3,4,5].

Figure 2 also shows that the fracture plane wasperpendiculartothe longitudinalplaneoftheshaft. Itwasindicated that crack propagation occurred under inducedflexuralfatigueloading.

Figure2.Modesoffailure:a.initialcrackportion(lower

arrow),andb.failureportion(upperarrow)

Therearethreeportionareaofthefailure,portionthatlargeplasticdeformationoccurs(largeportion),portionofbrittle fracture, and portion of rotational bending fatiguecharactaeristic.A large portion of the failure surface wasflattened and smeared off. This surface condition wasconsidereddue to a repeated grinding agains the fracturesurface with mating part while the motor runs aftercomplete fracture. The fatigue occurs because of pumpoperation over 40000 hours without preventivemaintenance.

Figure2showsthattherealsowasafatiguezone.Thefatiguezonecanbedescribedasfollows:asmoothrubbed,and velvety appearance, the presence ofwaves known as"clam-shells" or "oyster-shells", "stop marks" and "beachmarks," and the herringbone pattern or granular tracewhichshowstheoriginofthecrack,asseenatFig3[6].Ingeneral, stop marks indicate the variations in the rate ofcrackpropagationduetovariationsinstressamplitudeinacyclicapplicationvaryingwithtime.

Figure3.Failurezone

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29 JournalofVocationalStudiesonAppliedResearch,Vol.1(2),October2019

Figure4.Boltinpumpchamberanddamageofimpeller

Another cause of failure was worn out of shaft at

bearinglocation,thatcanbeseenatFig.4.Thiswearcausetheshaftcrosssectionareareducedand lacktowithstandtensile stress. The stress is a high stress level of inducefluctuatingstresses thatexerts fromastartandstopcyclemode of operation. The shaft experiences cyclic flexuralload and torsional loadduringpumpingoperation.At thislocation,anexcessiveplasticdeformationcouldbeinducedand severe localized stress occurs. This would lead tofatigue crack. The mass of shaft is an factor that inducecyclic flexural stress. This stress is distributed uniformlyalongthelengthoftheshaftbetweenthebearingsupports.Atthebearingsupport,reducedcrosssectionareainducesa local stress gradient then this stress could be thecontributortofailureoftheshaft.Thefilletcornerwastoosharp to withstand the stress concentration for longerduration.

Figure4.Shaftcrosssectionareareductioncausedbywearingout

ofbearingbushing

Vibratory stresswasalso suspectedas a shaft failurecontributor. The existence of sand and bolt in pumpchamber could generate vibration. This will induced avibratorystresssubjectedtotheshaft.

Unbalanced forceswhichresult fromforeignmaterialexist in pump chamber could results in large amplitudevibrations. Impellers may shift due to the decrease inresidual stresses that are created when the impeller iscooledandcontractedaroundtheshaft[7].Shaftvibrationsandflexingtendtoresultintheimpellercockingorbowingtheshaft,whichremoves it fromitsoriginalbalancealongitscenterline[8].

3.2.MaterialIdentificationAsspecification,pumpshaftconformtostainlesssteel

SS 316. This material has mechanical properties of yieldstrengthof21kg/mm2.

Material identificationwas carried out by using alloyanalyzer.TheidentificationcanbeseenatTable2.

Table2.MaterialIdentification

The table shows that material identification wasstainless steel SS304.The specificationof shaft is SS316.Both two materials were compare chemically andmechanically. The comparison canbe seen atTable3 andTabel4.

Table3.MaterialComparisonbetweenSS304andSS316

Table 3 shows that chemical composition of SS 304

andSS316issimilar.Theshaftwasmadeofstainlesssteelwhichisarecommendedmaterialforsuchapplications[Thechange of shaft by SS 304was accepted. It is also for themechanicalproperties.Thetwomaterialshaveasameyieldstrength,thatis21kgkg/mm2.

Table4.MechanicalPropertiesComparisonbetweenSS304and

SS316

3.3.ExcessivePowerOther main causes of pump failure that could cause

excessive power consumption.This could be cause of theliquidthatisbeingpumpedhasaviscositythatismorethanwhat the pumpwas designed for. The factorswas due tosand and bolt exist in pump chamber.This could lead the

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shaft tomisalign in thepump,and the impeller is touchingthecase.

4.Conclusiona. The mode of failure was consider that shaft

sustained a rotational load that cause the tensilestressoveritsultimatestrength..

b. ShaftwithmaterialofstainlesssteelSS304couldbeinterchangeablewith SS316, inmaterial propertiesidentificationpointofview.

c. The existence of sand and bolt in pump chambercould generate vibration. This will induced avibratorystresssubjectedtotheshaft.

5.AcknowledgmentThisworkwassupportedinpartbyVocationalSchoolof

DiponegoroUniversity.

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PumpVerticalDivision.[2] HeinzP.Bloch,FredK.Geitner,1997,MachineryFailureAnalysisand

Troubleshooting3rdEd.,GulfPublishingCompany,1997[3] Heinz P. Bloch, 2004, Root Cause Analysis of Five Cost Centrifugal

PumpFailure,Montgomery,Texas[4] Dr.JuergenWeinert,1998,Pumps:FailureModesFailureModesand

WaystoInvestigatetheCause,Wiesbaden,Germany[5] Farabirazy Albiruni, 2005, Failure of A Vertical Ammonia Transfer

Pump Shaft, Technical Bureau of Inspection, PT. Pupuk KalimantanTimur,Tbk.,Bontang,KlimantanTimur,Indonesia

[6] Roman Celin, Franc Tehovnik, Vodopivec, Borut Zuzek, 2013,Impeller-Blade Failure Analysis, Institute of Metal and Technology,Lepipot11,1000ljubljana,Slovenia

[7] OMPrakashandR.K.Pandey,1995,FailureAnalysysofTheImpellersofAFeedPump,EngineeringFailureAnalysis,Vol.3,No.1,pp.45-52,1996.

[8] Karassik, Igor J., J. P. Messina, P. Cooper, and C. C. Heald, PumpHandbook(3rdEdition).NewYork:McGrawHill,2001.