7/26/2019 Influence of Local Wall Thinning on Elastic Shakedown boundary of Pipe Bend.doc

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International Journal of Science and Research (IJSR)ISSN (Online): 2319-70!

I"#act $actor (2012): 3%3&'

Influence of Local Wall Thinning on Elastic

Shakedown boundary of Pipe Bend%% *+del-,han11. S%J +eid2/%R ase"3

1Departent of Design and Production Engineering!"aculty of Engineering! #in Shas $ni%ersity! &airo! Egypt

wagdy_ghany@hotmail.com

'Departent of Design and Production Engineering!"aculty of Engineering! #in Shas $ni%ersity! &airo! Egypt

sjebeid@yahoo.com

(Departent of Design!I)*+#TI&! &airo! Egypt

mohammedraafateljammal@gmail.com

*+stract: Studying the ductile failure mechanisms; reversed plasticity and ratcheting caused due to cyclic loads has received asubstantial attention for defect-free 90-degree pipe bends, however such data are scarcely found for those pipe bends suffering fromlocal wall thinning. This paper quantifies the effect of local wall thinning parameters on both elastic and shaedown boundaries viaa non cyclic-numerical technique developed by . The thinning geometry is assumed to be rectangular rather than circular but thegeometrical nonlinearities are considered. !inite and fully circumferential local wall thinning in pipe bends under combinedinternal pressure and in-plane bending; opening and closing have been studied. "oth e#trados and intrados local wall thinninglocations have been considered also.

eords:"inite Eleent! Pipe Bends! Shakedown! )e%ersed Plasticity! )atcheting! Local Wall Thinning,

1, Introduction

Pipe bends are considered the ost critical coponents inpiping systes! especially in nuclear power plants andnatural gas pipe lines, They are incorporated into piping

systes to allow odifications in isoetric routings and

aintain integrity of piping systes under transient loadingconditions by absorbing the theral e-pansions and seisico%eents by dissipating energy as a result of local plasticdeforation, *n the other hand due to their specific

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No"enclature E/ui%alent plastic stress

d Local wall thinning depth Liit stress of an elastic perfect plastic

ateriali

d Inner diaeter of pipe

od *uter diaeter of pipe )esidual noral stress coponents

E .oung0s odulus $ltiate tensile strength

L Length of straight pipe .ield strength

+ Inplane bending oent )esidual stress coponent+

i Increental inplane bending oent )esidual shear stress coponents

SD+ Shakedown liit oent2alf a-ial circuferential angle of local wall

thinning

P Internal pressure 2alf a-ial circuferential angle of local wall

thinning*P Liit pressure of sooth pipe bend

PE3 E/ui%alent plastic strain *++re5iations

) Pipe bend radius #erican petroleu institute

r +ean cross sectional radius of pipe #erican society for echanical engineers

t Thickness of pipe bend Elastic copensation ethod

,ree6 s"+ols Linear atching ethod+aterial initial yield strain "low accelerated corrosion

Pipe bend characteristics! '4 )t r "inite eleent

o5 Teperature difference "itness for ser%ice

Stress Inplane closingElastic stress coponent Inplane opening

Elasticplastic stress coponent Shakedown

*P Liit pressure of sooth pipe bend

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7/26/2019 Influence of Local Wall Thinning on Elastic Shakedown boundary of Pipe Bend.doc

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International Journal of Science and Research (IJSR)ISSN (Online): 2319-70!

I"#act $actor (2012): 3%3&'

deforation beha%iour when being used beyond their elasticliit! they are capable of plastici6ing o%er large areas whenthe syste is o%erstressed, 2owe%er! care ust be taken sothat deforations of the bend reain predoinantly elastic,*therwise! the resistance to deforation ay decreaserapidly leading to the failure of the syste, It is! therefore!iportant to know its collapse load for the safe operation ofthe plant, 7ot only do not the pipe bends suffer fro

con%entional applied loads! but they also suffer fro se%eralen%ironental effects such as erosion and corrosion, Erosionand corrosion effects can be found fro the inside runningfluid or outside corrosion fro the inside running fluid oroutside corrosion fro oisture or acidic edia, #ll thesetypes of attacks lead to general and locali6ed etal loss,

two ductile failure odes which are re%ersed plasticity orratcheting, When the structure is said to be shaking down! iteans that it beha%es fully elastically after a liitedperanent aount of elastic strain in the first loadingcycles, )e%ersed plasticity eans that the structure will ha%eplastic strain by the end of loading which is copletelyre%ersed by the end of unloading, +ore e%er! the structurewill fail after a certain nuber of cycles because of low

cycle fatigue, The other failure ode is called ratchetingwhich eans that the structure will accuulate plasticstrain during each loading and unloading cycle untile-hausting ductility and then reaches collapse, Bree 819:;ected to cobined internalpressure and cyclic inplane bending oent,

Shakedown doains for locally thinned elbows wereobtained %ia a noncyclic nuerical techni/ue were obtainedand full cyclic elastic plastic analyses were done to gainconfidence for the obtained boundaries, The shakedownboundary for locally thinned elbow= where the thinning didnot e-ceed the crown surface is alost the sae with thedefect free elbow at low internal pressure and it is affectedwith the increasing pressure,

References

U1V #bdalla 2"! +egahed ++ et al,.ounan +.#, # SiplifiedTechni/ue for Shakedown Liit Load Deterination,7uclear Engineering and Design, 'CC:='(;1'(1C,

U'V #PI Standard G;91#S+E ""S1! 'CC;! "itness"orSer%iceQ,

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UV +arriott DL, E%aluation of deforation or load control ofstresses under inelastic conditions using elastic finiteeleent stress analysis,

, Transactions of the #S+E PP Di%ision, 19HH=1(:(9,UGV Dhalla #, Siplified procedure to classify stresses for

ele%ated teperature ser%ice, Transactions of the #S+EPP Di%ision, 19H;=1'C1;;H,

U:V Seshadri ), Oenerali6ed local stress strain 8Oloss< analysis,Theory and applications, #S+E Xournal of Pressure esselTechnology, 1991=11('19';,

U;V &hen 2" et al,Ponter #)S, Shakedown and liit analyses for(D structures using the linear atching ethod,

International Xournal of Pressure essels and Piping,'CC1=;H(G1,

UHV #bdalla 2"! +egahed ++ et al,.ounan +.#, ShakedownLiit Loads for 9C Degree Scheduled Pipe Bends Sub>ected

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$iure 12: Loading during the full cyclic elastic plasticanalysis

$iure 13: Elastic and shakedown boundary ofpipe

bends with local wall thinning at e-trados under IP&oent

$iure 1!:Shakedown beha%ior of pipe bend with localwall thinning at e-trados at C,'Po 8Point1