管道应力师应知问题集锦Word文件下载.docx
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pressurethrustforcesappliedtoexpansionjointendswillbecompressive;
andbucklingisnotaddressedinCAESARII
临界失稳压力：
E—弹性模量（MPa）；
I—截面惯性矩（mm4/mm）；
v—泊松比，0.35—0.45；
Dm—管道平均直径；
C—椭圆修正系数，
，r1—椭圆管道的弯曲半径，r0—圆形管道半径；
允许的管壁冲击荷载：
2.Global/localloadsinC2output,Thereasonwhyweneedthelocalelementsloads?
为了获得作用在设备管口上准确的外载，以进行局部应力分析；
另外通过局部坐标推力的分析，可以仔细察看管道单元内部的相互作用关系，协助发现问题，并尽快找到答案。
3.Oninputsheet,whatisdifferentforForce,Uniformload,Rigidelementwithweight.-thetemperaturebaseofElasticmodulusinput?
集中力（力或弯矩作用于管道上一点，一般模拟外载力的作用效果，对于一些额外重量，如支架根部，最好不用力来输入，因为如果计算地震，这些质量都不存在。
）、均布载荷（荷载均布于管道所有点上，我们一般用它来模拟雪载）、带重量的刚性件（横向刚度无穷大横向没有弯曲，刚性件只传导位移和力，我们一般用它来模拟阀门，管道设备等，但要注意，刚性件有直径和壁厚，他们对他的横向变形会有影响。
）。
软件缺省的弹性模量是冷态的。
但用户可以选择。
4.Whatisnon-linearsystem?
Areathereanyspecialcautionsininput/outputfornon-linearcase?
非线性系统就是：
依据胡克定律F=K*X，我们认为k是变化的。
管道在使用支架、吊杆，支架加间隙，摩擦力的情况下，系统变成非线性的。
管系从冷态—>
热态或热态—>
偶然工况过程中由于非线性约束的作用导致管系刚度发生改变；
如果你输入过多的非线性支架，可能导致软件计算不收敛。
陷入死循环。
我们一般先判断，根据直观感觉决定一些点，加入非线性约束。
其他处根据计算结果，在调整支架。
5.Howtocheckthelift-offsupportpoint?
WhatshouldEngineercheckforlift-offproblem?
Whatishotsustainedstress?
检查约束报告，垂直方向受力为0的点即支架托空点；
支架托空点应考虑采用弹性支吊；
Hotsustainstress—计算热态持续应力。
依据B31.3AppendixP,用户可以校核热态持续应力。
主要是考虑支架脱空情况下持续应力。
GenerallyHotsustainedstressiscarriedoutbyremovingthesupportatthepointofliftoff,&
checkforsustainedstresses.Myquestionis:
-Isthereanyguidelinesoranyproperbasisavailableforneglectingsmallliftoffforhotsustainedstresscheck.IassumethatthemeaningofsmallliftoffmeansLiftoffbysmallpositivedisplacement..
Supposeu'
rsystemhasthreecases
1operating
2design
3Upset
Andinthesystemu'
rtwosupportaregoingtoliftoff（maybebysmalldisplacement）andduetotheremovalofthesetwosupportu'
rsystemgetfailedinsustainedcase...Whatucandohereisjustcheckwhetherthessetwosupportsareliftinginthesamecaseordifferent..iftheyliftindifferentcasecheckforremovalofonesupportatonetime...inmyviewushouldnotignoresmalldeflectionbecausetheywillactasconstantactingload....whichwillcausefailure
6.WhatisLiberalstressallowable?
一次应力的余量可以添加到二次应力的许用应力上来，我们将这个余量称为Liberalstressallowable。
Perhapsitwouldbeofsomebenefittoreviewthemeaningoftheterm?
liberalallowablestressrange?
.Firstofall,thisisnotatermthatisusedbytheASMEB31PressurePipingCodes.CaesarII（C2）usesthetermasasortof?
short-hand?
forreferringtotheincreaseinthermal（displacement）allowablestressrangethatisallowedinB31.1（paragraph102.3.2（D））andB31.3（paragraph302.3.5（d）.Intheseparagraphs,theB31Codesallowthepositivedifferencebetweenthecalculatedcombinedlongitudinalstresses（duetoweight（bending）andlongitudinalpressure）andthemaximumallowablestress,Sh,tobeaddedtotheterm?
0.25Sh?
（thesecondterm）intheequationforcalculatingthemaximumallowablestressrange,SA.TheB31Codessaythatit?
MAY?
beaddedintothe?
0.25Sh?
term,therebymakingitoptional.Iftheanalystelectstoignoretheadditionalallowablestressrangethedecision（allotherthingsbeingequal）wouldbejudgedconservative.Iftheanalystelecttoemploythisadditionalallowablestressrange,theresultingallowablestressrangeissometimestermed?
liberal?
.Itis,ofcourse,allsemantics.TheCodeallowstheadditionalallowablestressrangeforaverygoodreason.
TheconceptunderlyingthisruleisverywelldescribedinthefamousbookbyS.W.Spielvogle（PipingStressCalculationsSimplified,FifthEdition,1955）.SpielvogleexplainsthattheB31rulesintendfortheanalysttobeabletousetheentirerangeofstressfromthematerialyieldpointattheoperating（hot）temperaturetothematerialyieldpointattheambient（cold）temperature（lessafactorofsafety）.SinceSh（neglectingthepossibilityofcreep）issetat2/3Syforboththehotandcoldconditions,wecancalculatethehotyieldstressasSh*1.5andwecancalculatethecoldyieldstressasSc*1.5.Takentogetherthetotalallowablestressrangeforthecombinedloadingsofweight（bending）,longitudinalpressure（tension）andthermalexpansion（displacement）wouldbe（1.5*Sc）+（1.5*Sh）,or1.5（Sc+Sh）.Thisrangeofallowablestresshasbeenreducedslightlytoallowforthevagariesofmaterialandforother?
realworld?
inaccuracies.TheCodephilosophywouldthenpermitthetotalallowablestressrange（afterthefactorofsafetyisapplied）forallthecombinedloadingdescribedabovetobe1.25（Sc+Sh）（if,inthisdiscussion,weneglectthestressrangereductionfactorforsimplicity）.ButtheCodeuses1.0Shforthesustainedloadingsofweightandlongitudinalpressureandthisleaves1.25*Sc+0.25*Shfortheallowablethermalexpansion（displacement）stressrange（betyouwonderedwherethatcamefrom）.BecausetheCodeintendsfortheentirestrengthofthematerial（fromhotyieldtocoldyield）tobeused（exceptforthe?
adjustment?
madeforvagaries）,itfollowsthattheruleintheparagraphscitedaboveallowstheanalysttoputtheunused（differencebetweencalculatedsustainedlongitudinalstressesandtheallowable1.0*Sh）portiontouseinincreasingtheallowablethermalexpansion（displacement）stressrange.Youwillrecognizethatthe?
excess?
sustainedcaseallowablestresswillvaryacrossthesystembeinganalyzedandthatthevariationwilldirectlyreflecthowwellsupportedthesystemis（bendingstresseswillhavethegreatereffect）.Thisvariationin?
sustainedcaseallowablestressfromnodetonodeinthemodelwill（whenthe?
optionisused）resultintheallowablestressrange,Sa,beingdifferentateverynodewhentheCodecompliancereportisviewed.
So,onemightask,whywouldananalystopttonotusethe?
allowablestressrangeforcomparisontocalculatedexpansion（displacement）stressrange?
Thisisanengineeringjudgement.Forexample,ifthesustainedstresseswerecalculatedas80or90percentofShandthesystemwereoperatedinthematerial?
screeprange,thedesignermightwanttotaketheconservativedecisiontonotusethe?
allowablestressrangewhenevaluatingthermal（displacement）stressranges.Anotherexamplemightbeofferedasacasewhenthesystemisinseverecyclicservice（seeB31.3paragraph300.2forthedefinition）andthedesignerislookingforalongerfatiguelife.Goingthe?
conservative?
routemightalsoappealtothedesigner（orowner）ifthesystemwouldbeoperatingwithinthepressure/temperaturevariationsdescribedinparagraph302.2.4inB31.3orparagraph102.2.4inB31.1.Ifwehavesomedegreeofuncertainty,weemployanadditionalmeasureofconservatism.Asthesayinggoes,?
whenindoubt,builditstout?
.
Thankyouforbringingupthetopicfordiscussion.Goodluckwithyourprojects.
Ofcourse,alltheaboveisjustmyopinionanddoesnotreflecttheopinionofASMEoranyCodeCommittee.John.
AconservativeformulationoftheallowableexpansionstressrangeformanycodesinCAESARIIiscalculatedfrom:
f（1.25Sc+.25Sh）Whentheuserrequeststhatthe"
LiberalAllowable"
beused,thedifferencebetweenShandSl,providedSh>
Sl,willbeaddedtotheterminsidetheparenthesis,i.e.SA（Liberal）=f[1.25Sc+.25Sh+（Sh-Sl）]Theliberalexpressionwillonlybeemployedwhenthereisatleastonesustainedstresscaseintheloadset.Ifthereismorethanonesustainedstresscaseinasingleproblem,thenthelargestofSl,consideringallofthesustainedcases,foranysingleelementendwillbechosentosubtractfromSh.Becausethesustainedstressvariesfromonepipetoanother,theallowableexpansionstresswillalsovary.
7HowtoincorporatetheinstallationtemperatureinC2?
可在CII环境变量中更改环境温度；
环境温度在管道应力分析中是个很重要的设计条件，我们一般会去年平均的温度来进行考虑。
真正的环境温度是指管道安装最后焊缝施工时的环境温度，这样就可以决定安装的初态。
8.Whatisthermalbowingeffect?
管道暴露在阳光下，管道上部的温度和下部的温度会不同，管道会在这个温度作用下出现热拱效果。
9.WhatkindofpipingsystemshouldtheBourdoneffectbeconsideredto?
包尔登效应，盘管在压力作用下有伸直的效果。
一般是指弯头在压力作用下，有要伸直的效果。
Thereisapressure-sensingdevicecalledabourdontubewhichisacoiledflexibletubewithfluidpressureontheinside.Aspressureincreases,thecoiltendstowanttostraightenoutagainstspringpressure（sincethereisabiggersurfaceareaaroundtheoutsidecurveofthecoilthantheinsidecurveofthecoil...withsamepressureappliedonboth）.
Iwouldassumethatapipingelbowwantstostraightenoutforthesamereason.Thehigherthepressure,thehighertheforce...alsoprobablydependsonthegeometryoftheelbow.
thebourdoneffectisthedifferencebetweenthepressureinsidethetubeorpipeinrelationtothepressureoutsidethetubeorpipe.Iftheinsidepresurerisgreaterthantheoutsidepresurethetubeorpipewillexpand.Andifthetubeorpipeisbentinacircularform,theexpansionisnoticableandcanbeconvertedtoacalibratedreadingasinapressuregauge.
Electricpeteiscorrect.Internalpressurecanaffectthepipebendorelbowin2ways.TheBourdoneffectdescribesthetendencyforthepipebendto"
open"
underinternalpressureand"
close"
underexternalpressure.ThereasonisasdescribedbyElectricpete.Theotheref
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