Yuav ua li cas txheeb xyuas Sigma Phase Embrittlement hauv Aged Duplex Stainless Steel Heat Exchanger Cheebtsam?

Txawm hais tias ib daim ntawv duplex stainless hlau raj uas tau raug kub hnyiab tau ntev yuav tshwm sim tsis zoo, ib qho yooj yim kais nrog rauj tuaj yeem tawg nws. Qhov no yog qhov txaus ntshai tshwm sim hu ua sigma theem embrittlement, ib qho kev hloov pauv ntawm metallurgical uas, yam tsis hloov nws cov tsos, hloov lub zog, zawv zawg alloy rau hauv cov nkig ceramic. Kev tshawb pom ntxov ntawm sigma theem embrittlement duplex stainless hlau exchanger Cheebtsam yog qhov tseem ceeb vim nyob rau hauv -situ kho tsis ua tau thaum sigma tshwm sim. Nws yog ib qho tsim nyog los kho cov khoom puas.

Sigma Phase Embrittlement: Nws yog dab tsi?
Austenite thiab ferrite ua rau yuav luag sib npaug feem pua ​​​​ntawm qhov sib npaug microstructure pom hauv duplex stainless hlau (xws li 2205 thiab 2507). Lub zog siab, superior ductility, thiab zoo heev corrosion kuj yog tag nrho cov muab los ntawm no dual -phase qauv. Txawm li cas los xij, kev hloov pauv yuav tshwm sim thaum cov hlau duplex raug kub ntawm 600 thiab 900℃dhau lub sijhawm ntev. Ib theem tshiab intermetallic hu ua sigma (σ) yog tsim thaum theem ferrite pib tawg. Sigma muaj tetragonal siv lead ua qauv thiab yog hlau, chromium, thiab molybdenum compound. Nws yog nplua nuj nyob rau hauv molybdenum thiab chromium, heev nkig, thiab incredibly nyuaj.

Kub thiab lub sij hawm ob qho tib si cuam tshuam li cas sigma tsim. Kev hloov pauv tshwm sim sai tshaj plaws ntawm 750-850 degree; Qhov loj embrittlement tuaj yeem tshwm sim hauv ib teev. Nws yuav siv ntau pua lossis ntau txhiab teev ntawm qhov kub thiab txias (600-700 degree). Tsis muaj qhov siv tau hauv -situ kev kho cua sov uas tuaj yeem thim rov qab sigma thaum nws los nag, feem ntau yog me me, nyias daim hlau ntawm cov ciam teb thiab hauv cov nplej ferrite. Cov khoom siv yuav luag tag nrho poob nws qhov cuam tshuam hardness thiab ua nkig.

Feem ntau yog vim li cas rau qhov kub Exchanger
Cov xwm txheej hauv qab no yog cov feem ntau uas tshwm sim hauv sigma theem embrittlement:

Welds yam tsis tau tshaj tawm-weld solution annealing: Yog tias qhov txias qeeb, qhov kub- cuam tshuam thaj chaw (HAZ) nyob ib sab ntawm qhov vuam yuav nyob rau hauv qhov kub thiab txias rau lub sijhawm ntev. Tshwj xeeb tshaj yog qhov txaus ntshai yog loj, tuab daim. Sigma tseem nyob hauv HAZ yog tias cov khoom siv tsis yog tom qab cov tshuaj annealed (rhuab mus rau 1040-1100℃thiab sai sai quenched).

Kev ua haujlwm txuas ntxiv ntawm qhov kub thiab txias: Txawm tias tsis muaj tseeb, cov khoom siv hluav taws xob sib txuas ua haujlwm tsis tu ncua ntawm cov hlau kub ntawm 600 thiab 900℃yuav maj mam embrittle. Qhov no tuaj yeem tshwm sim nyob rau hauv ib qho kev sib pauv uas tsis txias kom zoo los yog hauv cov khoom siv hluav taws xob pov tseg.

Kev raug hluav taws kub: Txawm tias nyob rau lub sijhawm luv luv, cov nroj tsuag hluav taws kub ua kom sov ib feem ntawm qhov sib hloov pauv mus rau hauv qhov sib txawv ntawm cov sigma yuav ua rau muaj kev cuam tshuam hauv thaj chaw cuam tshuam.

Fabrication yuam kev: Sigma tuaj yeem txhawb nqa los ntawm kev kho cua sov tsis raug thaum lub sijhawm tsim khoom, xws li sluggish txias los ntawm annealing kub.

Cov cua sov- cov cheeb tsam cuam tshuam ntawm welds, thicker flanges, thiab cov nplooj ntawv raj yog cov chaw raug mob tshaj plaws. Txawm hais tias cov raj nyias nyias txias sai dua thiab tsis tshua muaj peev xwm tsim sigma, lawv tseem raug cuam tshuam yog tias qhov kev pabcuam kub siab heev.

Mechanical thiab Visual Indicators
Cov hlau lub ntsej muag zoo li tsis cuam tshuam los ntawm sigma theem embrittlement. Ib qho kev tivthaiv tuaj yeem tshwm sim zoo li qub, tsis muaj qhov pom tseeb tawg lossis tawg, tab sis nws yuav ua rau nkig heev. Txawm li cas los xij, nws lub neej tuaj yeem pom nrog kev kuaj xyuas thiab kev sim.

Fracture Surface Appearance
Cov pob txha tawg ntawm lub sigma-embrittled duplex steel yuav zoo li ci ntsa iab, granular, thiab crystalline uas tsis muaj ductile tearing lossis shear daim di ncauj yog tias cov khoom ua tsis tiav lossis yog lub hom phiaj tawg. Lub drab, fibrous tsos ntawm ib tug raug ductile fracture stands in stark contrast rau qhov no. Sigma muab cov hlau ua kom muaj zog ntawm lub chocolate bar; ib lub tshuab me me tawg nws es tsis txhob distorting nws.

Kev sim rau Impact Toughness
Charpy V-notch (CVN) cuam tshuam qhov ntsuas yog tus qauv kub rau kev suav cov sigma embrittlement. Thaum daws tau zoo-annealed, Duplex 2205 feem ntau muaj kev cuam tshuam toughness ntawm 100-200 J ntawm chav tsev kub. Lub toughness yuav txo qis dua 20 J thiab nquag mus rau ib daim duab thaum sigma tam sim no. Qhov kev sim no muaj cov pov thawj tsis meej rau cov khoom me me lossis cov ntawv xeem txiav tawm ntawm cov ntawv raj.

Metallographic Analysis: Qhov Tsaus Etch Spots
Tom qab etching, tus yam ntxwv ntawm sigma theem embrittlement yog pom nyob rau hauv ib lub microscope. Ib qho reagent tsim nyog, xws li electrolytic etching nyob rau hauv 10% oxalic acid los yog ib tug ua ke ntawm HCl thiab HNO₃ (Aqua Regia) los yog KOH (rau duplex), yog siv los etch ib tug polished qauv. Austenite thiab ferrite tshwm sim raws li ob theem sib cais nyob rau hauv ib tug raug duplex microstructure; austenite feem ntau yog daj ntseg lossis faintly etched, thaum ferrite yog tsaus dua. Nyob rau hauv lub ferrite nplej thiab raws li ib tug ciam teb, lub sigma theem manifests raws li ib tug maub, nquag blocky los yog phaj-zoo li network. Cov sigma hais lawv tus kheej tshwm sim raws li qhov sib txawv, tsis tshua muaj qhov tsaus ntuj ntawm qhov loj dua. Kev txheeb xyuas qhov zoo yog muab los ntawm qhov tshwj xeeb "dub etch me ntsis" lossis txuas ntxiv tsaus nti.

Ib qho kev hloov pauv ntawm qhov etched tuaj yeem ua rau ntawm -qhov chaw siv teb metallographic replication (raws li tau tham hauv kab lus dhau los), uas yog tom qab kuaj xyuas hauv lub tshuab ntsuas qhov ntsuas. Sigma tuaj yeem pom siv qhov tsis yog -kev puas tsuaj (lossis me ntsis kev puas tsuaj) yam tsis tau tshem tawm cov qauv los ntawm kev sib pauv loj.

ASTM A923 Kev Ntsuas Tus Txheej Txheem
Peb txoj kev lees paub yog muab los ntawm ASTM A923, "Txoj Kev Xeem Txuj Ci rau Kev Tshawb Fawb Txog Kev Tshawb Fawb Intermetallic Phases hauv Duplex Austenitic / Ferritic Stainless Steels," txhawm rau txheeb xyuas sigma thiab lwm theem intermetallic (xws li chi):

Txoj Kev A (Sodium hydroxide etch test): Ib qho rhuab 40% NaOH tov yog siv los kos cov qauv polished. Qhov tsaus nti etching cov tshuaj tiv thaiv qhia qhov muaj nyob ntawm sigma lossis chi theem. Qhov kev tshuaj ntsuam xyuas no muaj qhov tshwm sim dhau / tsis ua tiav.

Impact toughness raug soj ntsuam siv Method B (Charpy impact test). Kev lees txais yuav tsum muaj qhov nruab nrab qhov nruab nrab absorbed zog, xws li 54 J rau 2205.

Txoj Kev C (Ferrite cov ntsiab lus ntsuas): Qhov feem pua ​​​​ferrite txiav txim siab siv lub ferritescope. Cov ntsiab lus ferrite poob qis heev los ntawm kev tsim sigma. Txoj kev no, txawm li cas los xij, tsis yooj yim dua thiab raug cuam tshuam rau sab nraud.

Txoj kev ua tau zoo tshaj plaws rau kev pabcuam kev ua haujlwm yog Txoj Kev A (etch test) ntawm thaj chaw me me lossis ntawm ib qho kev hloov pauv.

Irreversibility: Tsis nyob hauv -Situ Repair
Qhov kev txiav txim siab tseem ceeb rau cov kws tsim vaj tsev cog qoob loo yog tias theem sigma tsis tuaj yeem raug tshem tawm los ntawm qhov loj, ua kom muaj cua sov los ntawm kev kho cua sov. Tag nrho cov khoom yuav tsum tau rhuab mus rau 1040-1100℃thiab sai sai quenched (siv dej los yog cov pa roj compressed) thiaj li yuav re-kua sigma. Ib qho hauv - kev pabcuam sib pauv nrog cov raj, gaskets, thiab cov kav dej txuas nrog tsis tuaj yeem ua tiav qhov no. Cov pob khoom sab hauv lub raj yuav nthuav dav thiab cuam tshuam txawm tias lub plhaub tuaj yeem ua kom sov, thiab qhov txias ceev yuav ua rau thermal shock. Yog li ntawd, ib qho tseem ceeb tivthaiv (xws li tubesheet los yog tuab flange) yuav tsum tau hloov sai li sai tau thaum sigma embrittlement raug txheeb xyuas. Cov kev xaiv nkaus xwb rau cov khoom siv raj yog tshem tawm thiab hloov.

Yog li ntawd, tus yuam sij rau averting kev puas tsuaj loj yog nrhiav kom tau. Kev tawg sai tuaj yeem tshwm sim los ntawm thermal lossis mechanical shock (xws li lub siab surge, rauj tshuab, los yog kev co tsis tu ncua) yog tias muaj teeb meem kub exchanger yog siv nrog embrittled qhov chaw.

Cov kauj ruam rau kev txheeb xyuas thaj chaw
Cov nram qab no yuav tsum tau ua nyob rau hauv ib tug qub duplex stainless hlau tshav kub exchanger yog hais tias sigma theem embrittlement yog xav tias:

Tshawb xyuas cov ntaub ntawv keeb kwm kev pabcuam kom pom tias qhov sib pauv tau puas tau raug kub siab tshaj 600 degree. Tshawb xyuas cov ntawv ceeb toom ntawm qhov xwm txheej hluav taws kub, cov ntawv teev kev ua haujlwm, lossis cov txheej txheem tsis raug cuam tshuam. Vuam cov ntaub ntawv: yog cov tuab tuab raug xa mus rau kev tshaj tawm -weld solution anneals?

Ua qhov ntsuas tsis yog -kev puas tsuaj ferrite. Ntawm qhov chaw huv, hauv av, kev nyeem ntawv ferritescope yuav qhia tau tias cov ntsiab lus ferrite qis dua (ib txwm nyob nruab nrab ntawm 40 thiab 60%; sigma tuaj yeem poob rau 30%). Tab sis qhov no tsis yog qhov tseeb ntawm nws tus kheej.

Xav txog kev tsim kho metallographic. ASTM A923 Method Ib txoj kev daws teeb meem yog siv los ua kom du, polishing, thiab etch ib cheeb tsam txwv (xws li lub ntsej muag ntawm cov ntawv raj lossis lub flange tuab). A 200-500 × magnification yog siv los tshuaj xyuas cov acetate reproduction. Embrittlement tau lees paub los ntawm qhov muaj nyob ntawm dub, blocky sigma theem tes hauj lwm.

Tau txais daim coupon me me yog tias koj ua tau. Rau qhov chaw kuaj Charpy cuam tshuam, ib lub raj luv luv lossis ib qho ntawm cov khoom seem ntawm qhov tsis yog - qhov chaw tseem ceeb tuaj yeem nqa tau. Kev mob hnyav yog qhia los ntawm qhov cuam tshuam lub zog ntsuas ntawm tsawg dua 20 J rau 2205 (los yog hauv qab specification).

Txiav txim siab qhov ceev: Cov cuam tshuam cuam tshuam yuav tsum tau teem sijhawm hloov pauv yog tias pom pom sigma. Nyob rau hauv ib ntus, txhua qhov chaw ntawm kev vibration yuav tsum tau kaw thiab lub exchanger yuav tsum tau khiav ntawm qis txhua yam thiab thermal loads.

Kev tiv thaiv muaj xws li kev kho cua sov kom tsim nyog thiab kev txwv kev pabcuam.
Tiv thaiv sigma embrittlement yog lub tswv yim zoo tshaj plaws los daws nws:

Ib txwm daws anneal duplex weldments: Post-weld tov annealing thiab ceev quenching yog xav tau rau cov seem tuab (ntau tshaj 6 hli). Txawm hais tias annealing muaj kev nyab xeeb dua, kev siv vuam zoo tsim nyog (tsawg tshav kub input, interpass kub tswj) feem ntau tuaj yeem tiv thaiv sigma rau nyias ntu.

A alternative alloy, such as a nickel-based superalloy, should be taken into consideration if a duplex exchanger is required for a high-temperature application (such as >500 degree) rau lub sijhawm ntev. Tsis txhob ncua kev pabcuam siab tshaj 600 degree.

Tswj kev ua kom txias tom qab muaj cua sov: Txhawm rau txo lub sij hawm siv nyob rau hauv 600-900 degree, lub exchanger yuav tsum tau txias kom sai li sai tau (piv txwv li, los ntawm dej nyab) thaum muaj hluav taws kub los yog thermal chim.

Hauv kev xaus
Tsuas yog kev kho cua sov kom zoo thiab tsis txhob ncua ntev rau nws qhov kev tsim qhov kub thiab txias tuaj yeem tiv thaiv sigma theem embrittlement, ib qho irreversible thiab catastrophic degradation. Ib qho kev poob qis hauv kev cuam tshuam, qhov ci ntsa iab tawg, thiab qhov tshwm sim ntawm qhov tsaus nti etch me ntsis lossis cov tes hauj lwm hauv kev tshuaj ntsuam metallographic yog cov cim ntawm sigma theem embrittlement duplex stainless hlau exchanger Cheebtsam. ASTM A923 Cov txheej txheem kuaj xyuas tus qauv yog muab los ntawm ASTM A923. Thaum kuaj xyuas, qhov kev puas tsuaj yuav tsum tau hloov vim nws tsis tuaj yeem kho. Thaum tshav kub kub muaj lub hwj chim los unwriting ib tug hlau lub neej; nyob rau hauv cov ntaub ntawv ntawm duplex stainless hlau, no unwritten taleas yog sigma embrittlement. Tsuas yog kev tiv thaiv tiv thaiv tus neeg nyiag khoom no, rhuav tshem - ua yeeb yam yog kev tshuaj xyuas niaj hnub, kev paub txog kev ua haujlwm kub hauv keeb kwm, thiab xaiv cov khoom tsim nyog.