ASME＋VIII-1＋2010英文版

ASME＋VIII-1＋2010英文版

(b)MinimumThicknessofPressureRetainingCompo-
nents. Exceptforthespecialprovisionslistedbelow,the
minimumthicknesspermittedforshellsandheads,after
formingandregardlessofproductformandmaterial,shall
be 1
⁄
16 in.(1.5mm)exclusiveofanycorrosionallowance.
Exceptionsare:
(1) theminimumthicknessdoesnotapplytoheat
transferplatesofplate-typeheatexchangers;
(2) thisminimumthicknessdoesnotapplytothe
innerpipeofdoublepipeheatexchangersnortopipesand
tubesthatareenclosedandprotectedfrommechanical
damagebyashell,casing,orducting,wheresuchpipes
ortubesareNPS6(DN150)andless.Thisexemption
applieswhetherornottheouterpipe,shell,orprotective
elementisconstructedtoCoderules.Whentheouterpro-
tectiveelementisnotprovidedbytheManufactureras
partofthevessel,theManufacturershallnotethisonthe
Manufacturer’sDataReport,andtheownerorhisdesig-
natedagentshallberesponsibletoassurethattherequired
enclosuresareinstalledpriortooperation.Wherepipes
andtubesarefullyenclosed,considerationshallbegiven
toavoidingbuildupofpressurewithintheprotectivecham-
berduetoatube/pipeleak.Allotherpressurepartsof
theseheatexchangersthatareconstructedtoCoderules
mustmeetthe 1
⁄
16 in.(1.5mm)minimumthicknessrequire-
ments.
(3) theminimumthicknessofshellsandheadsof
unfiredsteamboilersshallbe 1
⁄
4 in.(6mm)exclusiveof
anycorrosionallowance;
(4) theminimumthicknessofshellsandheadsused
incompressedairservice,steamservice,andwaterservice,
madefrommaterialslistedinTableUCS-23,shallbe 3
⁄
32
in.(2.5mm)exclusiveofanycorrosionallowance.
(5) thisminimumthicknessdoesnotapplytothe
tubesinaircooledandcoolingtowerheatexchangersif
allthefollowingprovisionsaremet:
(a) thetubesshallnotbeusedforlethalUW-2(a)
serviceapplications;
(b) thetubesshallbeprotectedbyfinsorother
mechanicalmeans;
(c) thetubeoutsidediametershallbeaminimum
of
3
⁄
8 in.(10mm)andamaximumof11
⁄
2 in.(38mm);
(d) theminimumthicknessusedshallnotbeless
thanthatcalculatedbytheformulasgiveninUG-27or
1-1andinnocaselessthan0.022in.(0.5mm).
(c)MillUndertolerance. Platematerialshallbeordered
notthinnerthanthedesignthickness.Vesselsmadeof
platefurnishedwithanundertoleranceofnotmorethan
thesmallervalueof0.01in.(0.25mm)or6%ofthe
orderedthicknessmaybeusedatthefulldesignpressure
forthethicknessordered.Ifthespecificationtowhichthe
plateisorderedallowsagreaterundertolerance,theordered
furnishedisnotmorethanthesmallerof0.01in.(0.25mm)
or6%underthedesignthickness.
(d)PipeUndertolerance. Ifpipeortubeisorderedby
itsnominalwallthickness,themanufacturingundertoler-
anceonwallthicknessshallbetakenintoaccountexcept
fornozzlewallreinforcementarearequirementsinaccor-
dancewithUG-37andUG-40.Themanufacturingunder-
tolerancesaregivenintheseveralpipeandtube
specificationslistedintheapplicableTablesinSubsection
C.Aftertheminimumwallthicknessisdetermined,it
shallbeincreasedbyanamountsufficienttoprovidethe
manufacturingundertoleranceallowedinthepipeortube
specification.
(e)CorrosionAllowanceinDesignFormulas. The
dimensionalsymbolsusedinalldesignformulasthrough-
outthisDivisionrepresentdimensionsinthecorroded
condition.
UG-17METHODSOFFABRICATIONIN
COMBINATION
Avesselmaybedesignedandconstructedbyacombina-
tionofthemethodsoffabricationgiveninthisDivision,
providedtherulesapplyingtotherespectivemethodsof
fabricationarefollowedandthevesselislimitedtothe
servicepermittedbythemethodoffabricationhavingthe
mostrestrictiverequirements(seeUG-116).
UG-18MATERIALSINCOMBINATION
Exceptasspecificallyprohibitedbyotherrulesofthis
Division,avesselmaybedesignedandconstructedof
anycombinationofmaterialspermittedinSubsectionC,
providedtheapplicablerulesarefollowedandtherequire-
mentsinSectionIXforweldingdissimilarmetalsaremet.
Therequirementsforthebasemetals,HAZ’s,andweld
metal(s)ofadissimilarmetalweldmentshalleachbe
appliedinaccordancewiththerulesofthisDivision.(For
example,ifacarbonsteelbasemetalisjoinedtoastainless
steelbasemetalwithanickelfillermetal,therulesofPart
UCSapplytothecarbonsteelbasemetalanditsHAZ,
PartUHAtothestainlesssteelbasemetalanditsHAZ,
andPartUNFtotheweldmetal.)
NOTE:Becauseofthedifferentthermalcoefficientsofexpansionof
dissimilarmaterials,cautionshouldbeexercisedindesignandconstruc-
tionundertheprovisionsofthisparagraphinordertoavoiddifficulties
inserviceunderextremetemperatureconditions,orwithunusualrestraint
ofpartssuchasmayoccuratpointsofstressconcentrationandalso
becauseofmetallurgicalchangesoccurringatelevatedtemperatures.[See
also GalvanicCorrosion inAppendixA,A-440(c),ofSectionII,PartD.]
UG-19SPECIALCONSTRUCTIONS (10