347 vs 321 Stainless hlau: Qhov ruaj khov siab -Temp Rivals

 

347 vs 321 Stainless hlau: Qhov ruaj khov siab -Temp Rivals

Nqe lus piav qhia:
Qib 347 thiab 321 yog titanium- thiab niobium-stabilized austenitic stainless hlau, feem. Ob leeg yog engineered los tiv thaiv intergranular corrosion tom qab vuam los yog siab - kub raug. Thaum feem ntau hloov pauv tau, 347 (niobium-stabilized) feem ntau muaj qhov zoo tshaj qhov ntev - lub sij hawm nkag siab thiab ruaj khov ntawm qhov kub thiab txias tsis tu ncua siab tshaj 800 ° C, ua rau nws yog qhov kev xaiv rau qhov kev thov siab tshaj plaws - kub siab daim ntawv thov.

Lub cev:

Lub hauv paus stabilization mechanism yog dab tsi, thiab nws txawv ntawm ob qib no li cas?
Ob qib tiv thaiv "sensitization" los ntawm kev khi cov pa roj carbon nrog cov carbide muaj zog dua - tsim cov khoom dua li chromium. Hauv 321, titanium (Ti) yog ntxiv ntawm qhov tsawg kawg nkaus ntawm 5 npaug ntawm cov ntsiab lus carbon los tsim cov titanium carbides ruaj khov. Hauv 347, niobium (Nb, tseem hu ua columbium) yog ntxiv ntawm qhov tsawg kawg ntawm 10 npaug ntawm cov ntsiab lus carbon los tsim niobium carbides. Qhov no tiv thaiv chromium depletion ntawm grain ciam teb. Qhov sib txawv tseem ceeb yog tias niobium carbides ruaj khov dua li titanium carbides ntawm qhov kub thiab txias, uas yog lub hauv paus rau 347 qhov kev ua tau zoo hauv qee yam kev siv.

Nyob rau hauv uas siab -kub kev lag luam daim ntawv thov yog 347 lub unequivocally nyiam los yog code-mandated xaiv?
347 feem ntau yog txoj cai-tseem ceeb lossis nyiam xaiv hauv kev lag luam tsim hluav taws xob rau lub tshuab hluav taws xob thiab lub tshuab hluav taws xob reheater, boiler panels, thiab siab - siab piping headers qhov kev pab kub siab tshaj 800 ° C nyob rau hauv kev ntxhov siab. Nws yog teev nyob rau hauv refinery rhaub, catalytic hloov kho units, thiab siab -kub tshuaj reactors. Nws qhov kev tiv thaiv zoo tshaj plaws rau "creep" (kev hloov pauv qeeb hauv qhov kev ntxhov siab ntawm qhov kub siab) ua rau nws tseem ceeb rau kev siab - khaws cov khoom tsim los rau ntev - kev pabcuam ntawm qhov kub siab, raws li cov qauv zoo li ASME Boiler thiab Pressure Vessel Code.

Puas muaj qee qhov xwm txheej uas 321 yuav nyiam tshaj 347 txawm tias qhov ua tau zoo sib txawv?
Yog lawm, 321 feem ntau nyiam thaum tus nqi yog tus tsav tsheb tseem ceeb, vim tias titanium feem ntau tsis tshua kim dua li niobium. Nws kuj tseem nyiam rau cov ntawv thov uas muaj cov kev pabcuam muaj zog nitric acid, qhov uas nws ua tau zoo. Rau cov khoom uas muaj qhov kub thiab txias tsis sib xws lossis kev caij tsheb kauj vab nrawm tab sis qhov chaw siab tshaj qhov kub siab qis dua 800 ° C - xws li hauv cov tshuab tso pa tawm, qee cov khoom siv hluav taws xob sib hloov, lossis cov twj tso kua mis nthuav dav -321 muab kev ua tau zoo thiab ua tau zoo txaus, ua kom muaj txiaj ntsig zoo.

Dab tsi yog qhov tseem ceeb welding thiab fabrication cov lus qhia tshwj xeeb rau txhua qib?
Rau 321, zoo heev tiv thaiv roj (feem ntau nrog argon backing) yog ib qho tseem ceeb thaum lub sij hawm vuam los tiv thaiv oxidation ntawm titanium, uas yuav ua rau nws stabilizing nyhuv ntawm weld. Rau 347, qhov no tsis tshua muaj kev txhawj xeeb. Ob qho tib si yuav tsum tau welded nrog cov khoom sib txuam hlau (ER321 lossis ER347). Ib qho kev txiav txim siab tseem ceeb rau cov neeg tsim khoom yog tias 321 txoj haujlwm- hardening tus nqi siab dua me ntsis. Rau ob qho tib si, tswj cov hluav taws xob hluav taws xob txo qis qhov dav ntawm qhov rhiab heev - cua sov - thaj tsam cuam tshuam. Tom qab-weld tov annealing yog pom zoo rau qhov siab tshaj plaws corrosion kuj nyob rau hauv cov kev pab cuam corrosive hnyav.

Yuav ua li cas tus engineer project ua tiav qhov kev xaiv thiab kev qhia tshwj xeeb ntawm 347 thiab 321?
Kev xaiv yuav tsum tau ua tiav raws li qhov tseeb hierarchy:Kub thiab Stressua ntej. Yog tias qhov ntsuas kub tsis tu ncua hauv kev ntxhov siab siab dua 800 ° C, qhia 347.Daim ntawv thov Codethib ob: ua raws li cov khoom pom zoo los ntawm txoj cai tsim qauv (xws li ASME).Corrosion Ib puag ncigthib peb: rau nitric acid, lean ntawm 321; rau oxidation dav dav, ob qho tib si ua haujlwm.Nyiaj txiagthib plaub. Ib txwm qhia tag nrho ASTM / EN qib (piv txwv li, ASTM A240 Qib 347) thiab xav tau cov ntaub ntawv kuaj xyuas zeb txheeb xyuas cov ntsiab lus stabilizing. Tsis txhob hloov ib qho rau lwm qhov yam tsis muaj kev tshuaj xyuas kev tsim vaj tsev.