1. Txheej txheem cej luam ntawm cryogenic steel
1) Cov kev xav tau ntawm cov hlau tsis tshua muaj kub yog feem ntau: muaj zog txaus thiab txaus toughness nyob rau hauv ib puag ncig uas tsis kub, zoo vuam kev ua tau zoo, kev ua tau zoo thiab corrosion kuj, thiab lwm yam. Ntawm lawv, tsis tshua muaj kub toughness, uas yog, muaj peev xwm. txhawm rau tiv thaiv qhov tshwm sim thiab nthuav dav ntawm cov pob txha tawg ntawm qhov kub thiab txias yog qhov tseem ceeb tshaj plaws. Yog li ntawd, lub teb chaws feem ntau hais txog qee yam cuam tshuam rau tus nqi toughness ntawm qhov kub qis tshaj.
2) Ntawm cov khoom ntawm cov hlau tsis kub, feem ntau ntseeg tau tias cov khoom xws li carbon, silicon, phosphorus, sulfur, thiab nitrogen deteriorate low-temperature toughness, thiab phosphorus yog qhov teeb meem tshaj plaws, yog li thaum ntxov low-temperature dephosphorization yuav tsum yog. ua thaum smelting. Cov khoom xws li manganese thiab npib tsib xee tuaj yeem txhim kho qhov kub thiab txias. Rau txhua txhua 1% nce hauv cov ntsiab lus npib tsib xee, qhov kev hloov pauv tseem ceeb tuaj yeem txo qis li ntawm 20 ° C.
3) Cov txheej txheem kev kho cua sov muaj kev txiav txim siab ntawm cov qauv metallographic thiab grain loj ntawm cov hlau tsis tshua muaj kub, uas tseem cuam tshuam rau qhov kub thiab txias ntawm cov hlau. Tom qab quenching thiab tempering kev kho mob, tsis tshua muaj kub toughness yog obviously txhim kho.
4) Raws li cov txheej txheem kub sib txawv, cov hlau tsis tshua muaj kub tuaj yeem muab faib ua cov hlau cam khwb cia thiab cov hlau dov. Raws li qhov sib txawv ntawm cov khoom sib xyaw thiab cov qauv metallographic, cov hlau tsis muaj kub tuaj yeem muab faib ua: cov hlau tsis tshua muaj hlau, 6% nickel steel, 9% nickel steel, chromium-manganese lossis chromium-manganese-nickel austenitic steel thiab chromium-nickel austenitic stainless hlau. tos. Cov hlau tsis tshua muaj hlau feem ntau yog siv nyob rau hauv qhov kub thiab txias li ntawm -100 ° C rau kev tsim cov khoom siv tub yees, cov khoom siv thauj mus los, chav tsev cia khoom thiab cov khoom siv petrochemical. Hauv Tebchaws Meskas, Tebchaws Askiv, Nyij Pooj thiab lwm lub tebchaws, 9% nickel steel yog dav siv hauv cov txheej txheem kub qis ntawm 196 ° C, xws li cov tso tsheb hlau luam rau kev khaws cia thiab kev thauj mus los ntawm liquefied biogas thiab methane, cov khoom siv khaws cia cov pa oxygen. , thiab tsim kua oxygen thiab kua nitrogen. Austenitic stainless hlau yog cov khoom siv zoo heev uas tsis muaj qhov kub thiab txias. Nws muaj qhov kub thiab txias toughness, zoo heev vuam kev ua tau zoo, thiab tsis tshua muaj thermal conductivity. Nws yog dav siv nyob rau hauv qis-kub teb, xws li thauj tankers thiab cia tso tsheb hlau luam rau cov kua hydrogen thiab kua oxygen. Txawm li cas los xij, vim nws muaj ntau cov chromium thiab npib tsib xee, nws kim dua.
2. Txheej txheem cej luam ntawm qhov kub tsis tshua muaj steel vuam siv
Thaum xaiv txoj kev siv vuam thiab kev tsim kho ntawm cov hlau tsis muaj qhov kub thiab txias, lub hom phiaj ntawm qhov teeb meem yog nyob ntawm ob yam hauv qab no: tiv thaiv qhov tsis zoo ntawm qhov kub thiab txias ntawm qhov sib koom ua ke thiab tiv thaiv qhov tshwm sim ntawm vuam tawg.
1) Bevel processing
Daim ntawv zawj ntawm cov hlau tsis tshua muaj steel welded pob qij txha tsis txawv ntawm cov ntsiab lus ntawm cov pa roj carbon zoo tib yam, cov hlau tsis tshua muaj hlau lossis cov hlau tsis muaj steel, thiab tuaj yeem kho tau li niaj zaus. Tab sis rau 9Ni Gang, qhib lub kaum sab xis ntawm qhov zawj yog qhov zoo dua tsis pub tsawg dua 70 degrees, thiab lub ntsej muag blunt yog qhov zoo dua tsis pub tsawg dua 3 hli.
Txhua qhov kub tsis tshua muaj hlau tuaj yeem raug txiav nrog oxyacetylene teeb. Nws tsuas yog hais tias qhov txiav ceev qeeb qeeb me ntsis thaum cov roj txiav 9Ni steel dua li thaum cov roj txiav cov pa roj carbon zoo tib yam. Yog hais tias lub thickness ntawm cov hlau ntau tshaj 100 hli, lub txiav ntug yuav tsum preheated rau 150-200 ° C ua ntej roj txiav, tab sis tsis ntau tshaj 200 ° C.
Gas txiav tsis muaj kev cuam tshuam rau cov cheeb tsam cuam tshuam los ntawm vuam cua sov. Txawm li cas los xij, vim nws tus kheej-hardening zog ntawm nickel-muaj steel, txiav nto yuav harden. Txhawm rau kom ntseeg tau tias qhov kev ua tau zoo ntawm kev sib koom ua ke welded, nws yog qhov zoo tshaj plaws los siv lub log sib tsoo kom zom cov npoo ntawm qhov txiav kom huv si ua ntej vuam.
Arc gouging tuaj yeem siv tau yog tias cov hlaws vuam lossis cov hlau hauv qab yuav tsum tau muab tshem tawm thaum siv vuam. Txawm li cas los xij, qhov saum npoo ntawm qhov thais yuav tsum tau sanded huv si ua ntej rov thov dua.
Oxyacetylene nplaim taws gouging yuav tsum tsis txhob siv vim muaj kev phom sij ntawm overheating cov hlau.
2) Xaiv txoj kev vuam
Cov txheej txheem vuam uas muaj rau cov hlau tsis tshua muaj xws li arc vuam, submerged arc vuam, thiab molten electrode argon arc vuam.
Arc welding yog feem ntau siv vuam txoj kev rau cov hlau tsis tshua muaj kub, thiab nws tuaj yeem welded hauv ntau txoj haujlwm vuam. Lub vuam kub input yog li 18-30KJ / cm. Yog tias siv cov khoom siv hluav taws xob tsawg-hydrogen electrode, qhov kev sib koom ua tiav zoo tuaj yeem tau txais. Tsis tsuas yog cov khoom siv kho tshuab zoo nkaus xwb, tab sis lub ntswj toughness kuj zoo heev. Tsis tas li ntawd, lub tshuab arc vuam yog qhov yooj yim thiab pheej yig, thiab cov cuab yeej siv peev txheej me me, thiab nws tsis cuam tshuam los ntawm txoj haujlwm thiab kev coj ua. qhov zoo xws li kev txwv.
Lub tshav kub input ntawm submerged arc vuam ntawm cov hlau tsis kub yog li 10-22KJ / cm. Vim nws cov khoom siv yooj yim, kev siv vuam zoo thiab kev ua haujlwm yooj yim, nws yog dav siv. Txawm li cas los xij, vim tias cov hluav taws kub rwb thaiv tsev ntawm cov flux, qhov cua txias yuav qeeb qeeb, yog li muaj kev nyiam ntau dua los ua kom muaj qhov kub kub. Tsis tas li ntawd, impurities thiab Si feem ntau tuaj yeem nkag mus rau hauv cov hlau los ntawm cov flux, uas yuav txhawb nqa qhov kev nyiam no ntxiv. Yog li ntawd, thaum siv submerged arc vuam, xyuam xim rau kev xaiv ntawm vuam hlau thiab flux thiab ua tib zoo ua haujlwm.
Cov pob qij txha welded los ntawm CO2 gas shielded welding muaj tsawg toughness, yog li lawv tsis siv nyob rau hauv qis kub steel vuam.
Tungsten argon arc vuam (TIG welding) feem ntau yog ua manually, thiab nws cov vuam kub input yog txwv rau 9-15KJ / cm. Yog li ntawd, txawm hais tias cov pob qij txha welded muaj cov khoom txaus siab, lawv tsis tsim nyog kiag li thaum cov hlau tuab tshaj 12 hli.
MIG welding yog feem ntau siv tsis siv neeg lossis semi-automatic vuam txoj kev nyob rau hauv qis kub steel vuam. Nws welding cua sov input yog 23-40KJ / cm. Raws li txoj kev hloov pauv hloov pauv, nws tuaj yeem muab faib ua peb hom: luv luv-circuit hloov txheej txheem (tso cua sov input), dav hlau hloov txheej txheem (ntau dua cua sov input) thiab pulse jet hloov txheej txheem (siab tshaj plaws tshav kub input). Kev hloov pauv luv luv MIG vuam muaj qhov teeb meem ntawm kev nkag mus tsis txaus, thiab qhov tsis zoo ntawm cov fusion tsis zoo yuav tshwm sim. Cov teeb meem zoo sib xws muaj nyob nrog lwm cov MIG fluxes, tab sis rau qib sib txawv. Txhawm rau ua kom lub arc ntau dua kom ua tiav qhov kev nkag mus tau zoo, ob peb feem pua rau kaum ntawm feem pua ntawm CO2 lossis O2 tuaj yeem nkag mus rau hauv cov ntshiab argon raws li cov roj tiv thaiv. Cov feem pua tsim tsim nyog yuav tsum txiav txim siab los ntawm kev sim rau cov hlau tshwj xeeb uas tau welded.
3) Kev xaiv cov khoom siv vuam
Vuam cov ntaub ntawv (xws li vuam pas nrig, vuam hlau thiab flux, thiab lwm yam) yuav tsum feem ntau yog raws li txoj kev vuam siv. Daim ntawv sib koom ua ke thiab groove puab thiab lwm yam khoom tsim nyog xaiv. Rau cov hlau tsis tshua muaj kub, qhov tseem ceeb tshaj plaws uas yuav tsum tau saib xyuas yog ua kom cov hlau vuam muaj qhov kub thiab txias txaus kom phim cov hlau hauv paus, thiab txo cov ntsiab lus ntawm diffusible hydrogen hauv nws.
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(1) Aluminium deoxidized hlau
Aluminium deoxidized steel yog qib steel uas muaj kev nkag siab zoo rau kev ua kom txias txias tom qab vuam. Feem ntau ntawm cov electrodes siv nyob rau hauv phau ntawv arc vuam ntawm aluminium deoxidized steel yog Si-Mn low-hydrogen electrodes los yog 1.5% Ni thiab 2.0% Ni electrodes.
Txhawm rau txo cov vuam cua sov cov tswv yim, aluminium deoxidized steel feem ntau tsuas yog siv ntau txheej vuam nrog nyias electrodes ntawm ≤ ¢ 3 ~ 3.2 hli, kom lub voj voog thib ob ntawm cov txheej txheej sab saud tuaj yeem siv los kho cov nplej.
Qhov cuam tshuam toughness ntawm weld hlau welded nrog Si-Mn series electrode yuav txo qis ntawm 50 ℃ nrog qhov nce ntawm cov cua sov. Piv txwv li, thaum tshav kub input nce los ntawm 18KJ / cm2 mus rau 30KJ / cm, lub toughness yuav poob ntau tshaj 60%. 1.5% Ni series thiab 2.5% Ni series vuam electrodes tsis dhau rhiab heev rau qhov no, yog li nws yog qhov zoo tshaj rau xaiv hom electrode rau vuam.
Submerged arc vuam yog feem ntau siv tsis siv neeg vuam txoj kev rau txhuas deoxidized hlau. Cov hlau vuam siv nyob rau hauv submerged arc vuam yog qhov zoo dua yog hom uas muaj 1.5 ~ 3.5% npib tsib xee thiab 0.5 ~ 1.0% molybdenum.
Raws li cov ntaub ntawv, nrog 2.5% Ni-0.8% Cr-0.5% Mo lossis 2% Ni welding hlau, sib phim nrog cov flux tsim nyog, qhov nruab nrab Charpy toughness tus nqi ntawm cov hlau weld ntawm -55 ° C tuaj yeem ncav cuag 56-70J (5.7 ~ 7.1 Kgf.m). Txawm tias 0.5% Mo welding hlau thiab manganese alloy yooj yim flux yog siv, tsuav yog cov cua sov input tswj hauv qab 26KJ / cm, weld hlau nrog ν∑-55 = 55J (5.6Kgf.m) tseem tuaj yeem tsim.
Thaum xaiv cov flux, kev saib xyuas yuav tsum tau them rau qhov sib piv ntawm Si thiab Mn hauv cov hlau vuam. Test pov thawj. Qhov sib txawv Si thiab Mn ntsiab lus nyob rau hauv cov hlau weld yuav zoo heev hloov tus nqi Charpy toughness. Cov ntsiab lus Si thiab Mn nrog tus nqi toughness zoo tshaj plaws yog 0.1 ~ 0.2% Si thiab 0.7 ~ 1.1% Mn. Thaum xaiv vuam hlau thiab yuav tsum paub txog qhov no thaum soldering.
Tungsten argon arc vuam thiab hlau argon arc vuam tsis tshua siv nyob rau hauv txhuas deoxidized hlau. Qhov saum toj no welding xov hlau rau submerged arc vuam kuj tseem siv tau rau argon arc vuam.
(2) 2.5Ni steel thiab 3.5Ni
Lub submerged arc vuam lossis MIG vuam ntawm 2.5Ni steel thiab 3.5Ni hlau feem ntau tuaj yeem welded nrog tib lub vuam hlau raws li cov khoom siv hauv paus. Tab sis ib yam li Wilkinson mis (5) qhia, Mn yog kub cracking inhibitor caij rau qis-nickel low-temperature steel. Khaws cov ntsiab lus manganese hauv cov hlau vuam ntawm li 1.2% yog qhov muaj txiaj ntsig zoo los tiv thaiv cov tawg kub xws li arc crater tawg. Qhov no yuav tsum tau coj mus rau hauv tus account thaum xaiv qhov sib xyaw ntawm cov vuam hlau thiab flux.
3.5Ni steel zoo li tempered thiab embrittled, yog li tom qab kev kho cua sov tom qab vuam (piv txwv li, 620 ° C × 1 teev, tom qab ntawd cub cua txias) kom tshem tawm cov kev ntxhov siab, ν∑-100 yuav poob qis los ntawm 3.8 Kgf.m mus rau 2.1Kgf.m tuaj yeem ua tsis tau raws li qhov xav tau. Lub vuam hlau tsim los ntawm vuam nrog 4.5% Ni-0.2% Mo series vuam hlau muaj ntau me me ntawm temper embrittlement. Siv cov vuam hlau no tuaj yeem zam cov teeb meem saum toj no.
(3) 9Ni hlau
9Ni steel feem ntau yog cua sov kho los ntawm quenching thiab tempering los yog ob zaug normalizing thiab tempering kom ua rau nws qhov kub thiab txias toughness. Tab sis cov hlau vuam ntawm cov hlau no tsis tuaj yeem raug kho kom sov li saum toj no. Yog li ntawd, nws yog ib qho nyuaj kom tau txais ib lub vuam hlau uas tsis tshua muaj kub toughness piv rau cov hlau hauv paus yog siv cov khoom siv vuam siv hlau. Tam sim no, high-nickel vuam cov ntaub ntawv feem ntau yog siv. Cov welds tso los ntawm cov khoom siv vuam zoo li no yuav yog austenitic kiag li. Txawm hais tias nws muaj qhov tsis zoo ntawm lub zog qis dua li 9Ni steel puag cov khoom siv thiab cov nqi kim heev, cov pob txha tawg tsis yog qhov teeb meem loj rau nws.
Los ntawm cov saum toj no, nws tuaj yeem paub tias vim tias cov hlau vuam yog austenitic kiag li, qhov kub tsis tshua muaj zog ntawm cov hlau vuam siv rau vuam nrog cov electrodes thiab cov xov hlau yog kiag li piv rau cov hlau puag, tab sis lub zog tensile thiab yield point yog. qis dua lub hauv paus hlau. Nickel-muaj steel yog nws tus kheej-hardening, yog li feem ntau cov electrodes thiab cov xov hlau them nyiaj rau kev txwv cov ntsiab lus carbon thiaj li ua tau zoo weldability.
Mo yog ib qho tseem ceeb ntxiv dag zog rau cov khoom siv vuam, thaum Nb, Ta, Ti thiab W yog ib qho tseem ceeb toughening ntsiab, uas tau txais kev saib xyuas tag nrho hauv kev xaiv cov khoom siv vuam.
Thaum tib lub vuam hlau siv rau vuam, lub zog thiab qhov hnyav ntawm cov hlau vuam ntawm cov hlau tsis sib haum yog qhov phem dua li cov MIG vuam, uas tej zaum yuav tshwm sim los ntawm qhov qeeb ntawm vuam qhov txias thiab qhov ua tau infiltration ntawm impurities los yog Si. los ntawm flux.
3. A333-GR6 tsis tshua muaj kub steel yeeb nkab vuam
1) Weldability tsom xam ntawm A333-GR6 steel
A333-GR6 steel belongs rau cov hlau tsis muaj qhov kub thiab txias, qhov kev pab cuam yam tsawg kawg nkaus yog -70 ℃, thiab nws feem ntau yog muab rau hauv lub xeev normalized lossis normalized thiab tempered. A333-GR6 steel muaj cov ntsiab lus tsis tshua muaj carbon, yog li lub hardening nyiam thiab txias cracking nyiam yog me me, cov khoom muaj zoo toughness thiab yas, nws yog feem ntau tsis yooj yim los tsim hardening thiab tawg tsis xws luag, thiab muaj zoo weldability. ER80S-Ni1 argon arc vuam hlau yuav siv tau Nrog W707Ni electrode, siv argon-hluav taws xob sib koom vuam, los yog siv ER80S-Ni1 argon arc vuam hlau, thiab siv tag nrho argon arc vuam los xyuas kom meej zoo toughness ntawm welded pob qij txha. Lub hom ntawm argon arc vuam hlau thiab electrode kuj tuaj yeem xaiv cov khoom uas muaj kev ua haujlwm zoo ib yam, tab sis lawv tsuas yog siv tau nrog kev pom zoo ntawm tus tswv.
2) Vuam txheej txheem
Rau cov ncauj lus kom ntxaws txheej txheem vuam, thov xa mus rau phau ntawv qhia txheej txheem vuam lossis WPS. Thaum lub sij hawm vuam, I-hom pob tw thiab tag nrho argon arc vuam yog saws rau cov kav dej uas muaj txoj kab uas hla tsawg dua 76.2 hli; rau cov kav dej uas muaj txoj kab uas hla ntau dua 76.2 hli, V-shaped grooves yog tsim, thiab cov txheej txheem ntawm argon-hluav taws xob ua ke vuam nrog argon arc priming thiab multi-layer filling yog siv los yog txoj kev ntawm tag nrho argon arc vuam. Txoj kev tshwj xeeb yog xaiv cov txheej txheem vuam sib xws raws li qhov sib txawv ntawm cov yeeb nkab kab thiab cov yeeb nkab phab ntsa thickness hauv WPS pom zoo los ntawm tus tswv.
3) Kev kho cua sov txheej txheem
(1) Preheating ua ntej vuam
Thaum lub ambient kub qis dua 5 ° C, lub vuam yuav tsum tau preheated, thiab lub preheating kub yog 100-150 ° C; qhov preheating ntau yog 100 hli ntawm ob sab ntawm lub vuam; Nws yog rhuab nrog oxyacetylene nplaim (neutral nplaim), thiab ntsuas qhov kub thiab txias Lub cwj mem ntsuas qhov kub ntawm qhov deb ntawm 50-100 hli los ntawm qhov nruab nrab ntawm qhov vuam, thiab cov ntsuas kub ntsuas cov ntsiab lus sib npaug sib npaug kom tswj tau qhov kub thiab txias. .
(2) Kev kho cua sov tom qab vuam
Txhawm rau txhim kho qhov tsis sib haum xeeb ntawm cov hlau tsis tshua muaj kub, cov khoom siv feem ntau tau quenched thiab tempered. Kev kho cua sov tsis zoo tom qab vuam feem ntau deteriorates nws qhov kev ua haujlwm kub qis, uas yuav tsum tau them nyiaj txaus rau. Yog li ntawd, tshwj tsis yog rau tej yam kev mob ntawm loj weldment thickness los yog nruj heev nruj tej yam kev mob, post-weld cua sov kev kho mob feem ntau tsis yog ua los rau cov uas tsis muaj-kub steel. Piv txwv li, kev vuam ntawm LPG cov kav dej tshiab hauv CSPC tsis tas yuav tsum tau kho cua sov tom qab vuam. Yog tias kev kho cua sov tom qab vuam yog qhov yuav tsum tau ua hauv qee qhov haujlwm, qhov cua sov, lub sijhawm kub thiab txias ntawm kev kho cua sov tom qab vuam yuav tsum nruj me ntsis raws li cov cai hauv qab no:
Thaum qhov kub siab tshaj 400 ℃, qhov cua kub yuav tsum tsis pub tshaj 205 × 25 / δ ℃ / h, thiab yuav tsum tsis pub tshaj 330 ℃ / h. Lub sijhawm ntsuas kub tsis tu ncua yuav tsum yog 1 teev ntawm 25 hli phab ntsa tuab, thiab tsis pub tsawg dua 15 feeb. Thaum lub sijhawm ntsuas kub tsis tu ncua, qhov kub sib txawv ntawm qhov siab tshaj plaws thiab qhov qis tshaj plaws yuav tsum qis dua 65 ℃.
Tom qab qhov kub thiab txias, qhov txias txias yuav tsum tsis txhob siab tshaj 65 × 25 / δ ℃ / h, thiab yuav tsum tsis txhob siab tshaj 260 ℃ / h. Cov cua txias yog tso cai hauv qab 400 ℃. TS-1 yam khoom siv kho cua sov tswj los ntawm lub computer.
4) Kev ceev faj
(1) nruj me ntsis preheat raws li cov kev cai, thiab tswj lub interlayer kub, thiab interlayer kub tswj ntawm 100-200 ℃. Txhua qhov vuam seam yuav tsum tau welded nyob rau hauv ib lub sij hawm, thiab yog hais tias nws yog interrupted, qeeb txias ntsuas yuav tsum tau ua.
(2) Qhov saum npoo ntawm lub vuam yog nruj me ntsis txwv tsis pub khawb los ntawm arc. Lub arc crater yuav tsum tau sau thiab qhov tsis xws luag yuav tsum yog av nrog lub log sib tsoo thaum lub arc kaw. Cov pob qij txha ntawm cov khaubncaws sab nraud povtseg ntawm ntau txheej vuam yuav tsum staggered.
(3) nruj me ntsis tswj cov kab hluav taws xob, txais yuav me me tam sim no, tsis tshua muaj hluav taws xob, thiab vuam ceev. Lub vuam ntev ntawm txhua W707Ni electrode nrog lub cheeb ntawm 3.2 hli yuav tsum siab tshaj 8 cm.
(4) Kev ua haujlwm hom ntawm luv arc thiab tsis muaj viav vias yuav tsum tau txais yuav.
(5) Kev nkag mus rau tag nrho cov txheej txheem yuav tsum tau txais, thiab nws yuav tsum tau ua raws li nruj raws li cov kev cai ntawm cov txheej txheem vuam specification thiab daim npav txheej txheem vuam.
(6) Lub zog ntawm qhov vuam yog 0 ~ 2 hli, thiab qhov dav ntawm txhua sab ntawm qhov vuam yog ≤ 2 hli.
(7) Kev ntsuam xyuas tsis muaj kev puas tsuaj tuaj yeem ua tiav tsawg kawg 24 teev tom qab qhov kev kuaj pom qhov vuam tsim nyog. Pipeline taub qab vuam yuav tsum raug rau JB 4730-94.
(8) "Lub Hwj Hwj Hwj Hwj Hwj Hwj Hwj Hwj Hwj Hwj Hwj Huv: Tsis Muaj Kev Ntsuas Kev Ntsuas Ntawm Lub Hwj Hnyav" tus qauv, Chav Kawm II tsim nyog.
(9) Weld kho yuav tsum tau ua ua ntej tom qab vuam kub kho. Yog tias tsim nyog kho tom qab kev kho cua sov, lub vuam yuav tsum rov ua kom sov tom qab kho.
(10) Yog hais tias qhov geometric dimension ntawm weld nto tshaj tus qauv, kev sib tsoo raug tso cai, thiab lub thickness tom qab sib tsoo yuav tsum tsis txhob tsawg tshaj li qhov yuav tsum tau tsim.
(11) Rau kev vuam tsis xws luag, qhov siab kawg ntawm ob qhov kev kho yog tso cai. Yog tias qhov kev kho ob qho tseem tsis tsim nyog, lub vuam yuav tsum raug txiav tawm thiab rov ua dua raws li cov txheej txheem vuam tiav.
Post lub sij hawm: Jun-21-2023
