case study 1-final report-fa-pt. sulzer turbo services indonesia
TRANSCRIPT
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
1/24
FAILUREANA LYSIS
REPORT
Case StudyGroup 1
StudBolt Failure
duetoHydro e!E"#rittle"e!t
Te$%!i$al Report
Metallurgy and MaterialDepartmentmakes no representations or warranties,eithe
r expressed or implied,
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
2/24
and specificallyprovides the results ofthis report “asis” basedon
the informationprovided by clien t
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
3/24
Executive Summary
PT.SulzerTurboServicesIndonesiareportedthatitsstudbolthad failedinservice. AsreportedbyPT.SulzerTurboServicesIndonesia,thefailure occurredonthe
threadpartofthestud bolt.Thethreadwaslocatedonbothendsofthestudboltbut thefailed
partonly occurredonone endofthestudbolt.Ourstudy showedthatthe studbolt failed
due to hydrogenembrittlementthatresultedfromitslonge posureto hydrogengas
atmosphere duringoperation. Thepresenceofthe areawitha number
oflocalizedprecipitatesinthe failedstudboltacceleratedthe failurebecausethis
localizedprecipitates wasthemostfavorablesitefor hydrogenmoleculesthatcame from
the inner container to re!combined and then produced the pressurized
hydrogengas in themetal. Once this pressurized hydrogengas e isted,it wea"ened
the bondingbetween metalatoms.As aresult,thestudbolt materialfracturedin a
brittlemode.Inmostcases,oncethehydrogengasis
formedinthemetalandandwea"ensthemetal atombonding,thecrac" propagationwould
occurautomatically withoutthe e ternal stress becausethis produced hydrogen has
enough pressureto create andpropagate thecrac"s.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
4/24
Background Information
PT. SulzerTurboServicesIndonesiareportedthatitsstud bolthad failedin
service.AsreportedbyPT.SulzerTurboServicesIndonesia,the failureoccurredon
thethread part ofthestud bolt. Thethreadwaslocatedon both ends ofthestudbolt
butthe failedpartonly occurredononeendofthestudbolt.Principally,theboltis
usedto#ointwo parts li"eflange or others. Thebolt hastwo$%&similar nuts on each
endwhichistightenedduring application.'igure(illustratesthe principalwor"of
studboltin#oiningmethod.Thefailedsamplewasthensubmittedto)*P'Afor
failure analysis$'ig. %&.
Objectives
The assessmentwas carried out in *etallurgyand *aterial +epartment,
niversity ofIndonesia,inordertofindouttherootcausefailureofstudboltandto ma"e
recommendations.
Thescope ofwor" wasasfollows-
(. .%.
/.
4. ………………………………………………………………………….
InvestigationResults
Visualexamination
The failedstud bolt was visually e amined and photographed in as!received
condition$'ig.(&.'orabetter e amination,thefracturesurfaceofthefailedstudbolt
wasobservedbyopticalmicroscopeatmagnificationof01$'ig.%&.Asobserved
fromthemacrophotography,thecrac"seemstobeinitiatedfromaspotatthe
threadandtopropagateinacircumferentialmode.Thecrac"surfacehadawide
smooth area$crac"propagationroute& androugharea$final rupture&.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
5/24
Chemical Com osition!est
Inorder toobtaininformation aboutthechemical composition,thesamplewasthen
sub#ectedtothechemicalcompositiontest usingOptical 2missionSpectroscopy
$O2S&.Table(showsthechemicalcompositionoffailedsamplein comparisonwith
AST*A3456rade 4/7.Theresults revealthatthere isaslight differencebetween
thenic"el$8i&contentsinthetestedsample andtheoneinthestandard. Thetested
samplecontains 3.(/98i,whichis 7.(/9 higher thanthe ma imum nic"elcontent
allowedforAST*A3456rade/7 material$/.7!3.798i&.Theother elementscomply
withthestandard materialre:uirement, as canbeseeninthetable.Thisslight
differenceinnic"elcontentmay notsignificantly impairthemechanicalproperties of thestud bolt.8ic"el isintentionally addedtointroduce the toughness intothis type of
material.
!ensile !est
The tensiletest was conducted to obtain the information about mechanical
properties ofthe bolt, i.e.tensilestrength, yieldstrengthand elongation. Table%
showsthetensile propertiesofsampleincomparisonwithAST* A3456rade4/7.
Thetensilestrengthofthe failedtestedsampleis(%53*Pa,whichisabout43*Pa below
thestandard material.Itsyieldstrengthis(%%3*Pa,whichis33*Pahigher than
overthestandard materialanditselongationis (7.;49$7.;49higherthanthe
standardmaterial.
"ardness test
Toobtainanother mechanical propertiesinformation,hardnesstestwasperformed
onthefailedsample.Table/showsthehardnessvalueofsampleincomparison
withAST*A3456rade4/7.Theresultshowsthatthehardness valueisslightly below
theminimumvaluere:uiredby thestandard.Thefailedsamplehasa hardness
valueof/;
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
6/24
Informationobtainedfromthe microstructure photosisthat the basematerialofthe
studboltcontains martensite phases.Thecrac"propagating along thegrain
boundarywas observed onthefailedsample.
$ractogra hyanalysis by SE# and E%S
The fracturesurface wasobservedusingScanning2lectron*icroscopy $S2*&to
gathermoreinformationabouttheinitialcrac"sandotherrelatedfactorsaffecting the mode
offailure. The2+Sanalysiswasalsoperformedonthe fracturesurface to
analyzeanypossiblecontributionofenvironmentormicrophaseofthematerialto the
failure.Thecrac"propagatingfromthethreadwasobservedonboththefracture
surfacesofthefailedsample.'igure ; and> showthe propagatingcrac".
The fracturesurface observed fromS2*imagesindicatesthatitisbrittle fracture
sincenoevidence ofdimpleslocatedinthe fracturearea. Thepresencesofdimples
indicatethat the fracturemodeisductile. ?rittlefracturecanbe intergranularor
transgranular.Intergranularbrittle fracturecanbetheresultofembrittlement along
thegrainboundaries.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
7/24
Precipitateswerefoundwithinthematri ofbase metalsinceitisaprecipitate!
hardenedstainlesssteel@itmainly composed of'e!)r.?utan anomalywasfound
thattheprecipitateswithinthefailedsamplewereconcentratedat onepoint.Some
precipitateswereaccumulated at some spot onthe thread edge.Table 5showsthe
2+Sresultsofthetestedspot.Theseinhomogeneouslydispersedprecipitateswere
observedusing?ac"scatteredSecondary2lectron$?S+&.Somecrac"swerefound
tobeinitiatedfrom these precipitates.
?ased onthe2+Sresultsshowed onTable 5and3,thecompositionof'e and)r
thedar" spotandthe basemetal is :uitethesame.Itcanbeconcludedthatthedar"spotsare precipitatethatcomposedof'e and)r.Precipitates, incaseforthis stainless
steel, areintroducedtogivestrengthtothematerial. Some disadvantages
arethenfoundiftheyarenotwelldispersed$inhomogeneous&.
The accumulated precipitates could generate wea" areasincestress concentration
willbelocatedonthatspot.Thiswillbetheinitialspotforfatiguecrac"propagation.
Afatiguecrac"willtypicallyinitiateatadiscontinuityinthematerialwherethecyclic
stressisma imum.Sincethestudbolde periencedthetensilestressandalsovibrationduringapplication,thecombinationoftensilestressandvibrationcould
facilitate thefatiguefailure tooccur..
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
8/24
%iscussion
Thestudboltiscommonly usedasa fastener to#ointwoparts altogether@thepart suchas
flangeis#oinedusingthis"indofbolt$see $ig&' &.?ased onthechemical
compositiontest$see !able' & andmetallographice amination$see $ig& ()*+ , &,
thestud boltwasmadeofprecipitated!hardenedstainlesssteel
withmartensitephasematri .The2+Simage analysis results showed
thattheprecipitates$see $ig&
'' & mainly composed of'e!)rthatcame fromthealloying elementsofthestainless
steel.Inpractice,whenthenutisfastened,astress$tensile&isthenintroducedto
thestudbold. Sincetheboltwasapplied onaturbine part,thevibration during itsoperationcouldbealsotransferredtotheboltgeneratingacyclicload. The
combinationbetweenatensilestressandavibrationcouldpossiblytriggerthe
fatiguefailure.
Theboltswereappliedontheturbinesystemconsumingfuelmainlycomposed of
nitrogen$8 %&andhydrogen$< %&withsmall fractionofargon$Ar&,methane$)< 5&,
carbondio ide$)O %&andcarbonmono ide$)O&.Thecorrosivegasinthissystem
is)O %.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
9/24
thethread$see $ig& '1 &@someprecipitateswereaccumulated generating stress
concentrationspotonthethread$see $ig&'-+'. &.Thehard precipitated particles could
beafactor forcrac"initiationsinceama imumstresswillbemainly accumulatedat or
focusedonthoseparticleswhenthestressis wor"inginthe material@ moreover,this
effectwillbecatastrophic ifthe precipitatesare accumulated atcertainspotonthe
bolt.?asedontheS2* observation,anumberofprecipitates
werefoundatthethread$see $ig& '. &@that ma"ethis locationasthewea"estspot andcould
fail duetocyclic load$fatigue&.8evertheless,it mightbe notindicatingthat
fatiguewastherootcauseofthefailure.Itwaspossiblytriggeredby otherinitiation
sinceverylittle evidencefounduponthefacture surface.
Theindicationofembrittlement duetohydrogenwas also observed.?ased ontheS2*images,thecrac"spropagated alongthegrainboundary. 8oevidences of
dimplewere observedonthsductilematerialthusindicating thatthecrac"s
propagatedduetoembrittlement$see $ig&'( &.Theatmospherecontainshydrogengas$< %&
thatpossiblybethesourceofhydrogenatomsdiffusingintothemetal
matri creatingembrittlement.
Ascan beseeninTable 4, hydrogengasma"esup almost 059 ofthetotal gascompositioninthesystem.Inthiscase,the othergases may beconsideredasthe
impurities. Severalliteratureshavereportedtheeffectsofhydrogenembrittlement of
gaseousimpurities.6asimpuritiescaninhibit,accelerate, orhavenoeffectupon
hydrogenembrittlement.Asdocumentedelsewhere,)< 5 and8 % gaseshaveno
effectonhydrogenembrittlement,< %Sand)O %gases act as accelerators of hydrogen
embrittlement 4B.
Along e posureofthemetalli"ethestud bolttothehydrogengasinthecontainer could
promotethehydrogenatomsto
migrateintothemetalmatri .Someofthehydrogenatomsre!combinedwithcarbon atoms
toformmethane gas$)< 5&inside minusculevoids.The
methanegascreatedpressurewithinthe minusculevoids$see $ig&', &
thatcouldreducetheductility ofa metalcreatingembrittlement.8ot only
withintheminuscule voidswherehydrogenwaspresentbut also withinthegrain
boundariessincetherewerealsocavitiesdue tothedisorder arrangementofatomicdirection.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
10/24
Thefailedstudboltwase posedtotherelatively hightemperature $around(47C)&.
Accordingtotheliterature,underambient temperature,hydrogenatomscanbe
absorbedtothe metallatticeanddiffusethroughthegrainboundaries.Thecrac" inducedby
stress underthisconditionwillpropagatetransgranularly.Otherwise, under
hightemperature,theabsorbed hydrogenatomstendtogatherinthegrain
boundariesandthecrac"swill propagateintergranularly 5B.Someresearchers
describethetheappearanceas beingsimilartobro"enroc"candy >B.Thistypeof bro"en
roc" candy!li"e fracture can be seen in 'igs. %7 and %(.In addition,the
hydrogeninthecontainer also diffusesinto the metal,gravitating towardsthe area
withthegreateststress ;B.Inthecaseofthis failedstudbolt,the areawiththe
greateststress isthe areacontaininga localized precipitation$see $ig& '' &.
AS*2?oilerandPressureDessel)ommittee (7Bestablishedthe hydrogenstorage
container pro#ectteamin%775statesthatthe ma imumwor"ing pressure forthis
systemis(7/*pa,whichismuchhigherthantheactualwor"ingpressurein SulzerEs
system,i.e. around4*pa$around47?ar&. Thus,thereis noissueof overpressurecontributingto thefailure.
Conclusion
Thestudboltfailed duetohydrogenembrittlementthatresulted fromitslong e posureto
hydrogengas atmosphereduring operation.Thepresence ofthearea
withanumberoflocalizedprecipitatesinthefailedstudbolt acceleratedthefailure
becausethislocalizedprecipitates wasthemostfavorablesitefor hydrogenmoleculesthat camefromtheinnercontainertore!combined andthenproducedthe
pressurizedhydrogengasinthe metal.Once this pressurizedhydrogengas e isted,
itwea"enedthebonding betweenmetal atoms.Asaresult,thestudboltmaterial
fracturedina brittlemode.Inmostcases,oncethehydrogengasisformedinthe metal
andandwea"ensthe metal atombonding,thecrac"propagationwouldoccur
automaticallywithoutthe e ternalstress becausethisproducedhydrogenhas enough
pressuretocreateand propagate thecrac"s.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
11/24
Recommendations
(. sethematerial withtheunwantedprecipitates as lowas possible.
%. Athouroughmaterial selectionstudyalongwith thelaboratorytestare
commonlyre:uiredforthematerials thatwould becontinuouslye posedto
hydrogengas.
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
12/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
13/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
14/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
15/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
16/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
17/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
18/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
19/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
20/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
21/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
22/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
23/24
-
8/16/2019 Case Study 1-Final Report-FA-PT. Sulzer Turbo Services Indonesia
24/24
Reference
(. 'atigue'ailure =esultingfromDariableFoading$ h ttp -GGh ig he re d .m c g r a w!
h ill.c om Gsi te sG d lGf r e e G77 0/ ( %( > /% G/4 3 0 4 4 Gc ha p te r7 4 .p d f &
%. 'ractography,AS*