Puas yog Txias Khoov ntawm 316 Stainless Steel Sheath Tubes rau U-Shole Immersion Heaters Transform Retained Austenite into Strain-Induced Martensite and Accelerate Pitting in Low-Chloride High-Tsev Dej?

Kev pheej hmoo metallurgical ntawm kev tsim U-puab lossis kev cai khoov 316 stainless hlau hluav taws xob cua sov raj feem ntau tsis pom zoo rau cov qauv kev xav tau corrosion. Cov txheej txheem ntawm dabtsi yog khoov, tshwj xeeb tshaj yog thaum siv me me radii ntawm txias drawn tubing, ua rau cov yas deformation, uas hloov cov metastable retained austenite rau hauv strain-induced martensite. Qhov kev hloov pauv no txo ​​cov txiaj ntsig zoo sib npaug ntawm tus lej (PREN) ntawm thaj chaw khoov, txawm tias cov khoom siv hauv paus tau ua tiav raws li 316 qhov kev xav tau. Kev ntsuas hluav taws xob hluav taws xob ntawm cov ntaub ntawv sim qhia tau tias qhov ntsuas kub tseem ceeb (CPT) hauv qhov txias khoov ntawm 316 stainless hlau sheaths tuaj yeem yog 15-25℃qis dua qhov tsis sib xws ntawm tib lub tshav kub. Hauv cov ntawv thov uas cov dej tsis tshua muaj chloride tab sis qhov kub thiab txias (piv txwv li, 80 txog 95 degrees C, 50 txog 100 qhov chaw ntawm ib lab Cl⁻), qhov kev txo qis no feem ntau txav mus rau qhov chaw khoov los ntawm lub xeev passive mus rau active pitting xeev nyob rau hauv lub hlis ntawm kev pab cuam, ua rau lub sij hawm ua ntej lub rhaub tsis ua hauj lwm. Tsab ntawv xov xwm no soj ntsuam kev sib koom ua ke ntawm kev khoov lub vojvoog, strain-induced martensite feem thiab pitting susceptibility thiab muab cov txheej txheem xaiv rau cov kws tsim qauv tsim cov qauv tsim 316 stainless hlau immersion rhaub rau nruab nrab cov dej hauv dej.

Metallurgical Mechanism of Strain -Induced Martensite in Cold Bent 316 Stainless hlau
Cov qauv austenitic ntawm 316 stainless hlau yog thermodynamically ruaj khov tsuas yog ntawm ib qho kev ua txhaum lub zog. Hauv qab qhov kub ntawm martensite (Ms), lub tshuab deformation yog txheej txheem ua haujlwm txias uas lub zog tau txais txaus los txhawb kev hloov pauv ntawm lub ntsej muag -centered cubic austenite ($\\gamma$) rau lub cev -centered tetragonal martensite ($\\alpha'$). Ms kub ntawm 316 stainless hlau yog hais txog -40℃. Txawm li cas los xij, strain-induced martensite pom nyob rau hauv chav tsev kub rau cov yas yas tiag tiag ntau dua qhov tseem ceeb. Khoov ua rau muaj kev ntxhov siab rau sab nraud ntawm cov ntaub qhwv thiab compression ntawm cov fibers sab hauv. ε=t/2R Qhov twg R yog lub vojvoog khoov mus rau lub raj nruab nrab, t yog phab ntsa tuab, thiab ε yog qhov siab tshaj plaws yas lim rau ntawm tensile sab. Rau 2D khoov ntawm tus qauv 12 hli OD raj nrog 1.2 hli phab ntsa tuab mus rau qhov nruab nrab ntawm lub vojvoog ntawm 24 hli cov txheej txheem fiber ntau yog 0.05 (5%). Ntawm 15 hli vojvoog (1.25D khoov), qhov kev sib tw nce mus rau 0.08 (8%). Kev ntsuas nrog Fischer Feritscope qhia tias nyob rau hauv 316 stainless hlau ib tensile strain ntawm 5% ua rau kwv yees li 8-12% a' martensite thiab 8% strain tshwm sim nyob rau hauv 15-25% martensite.

Martensite ntau lawm muaj ob qhov cuam tshuam rau corrosion kuj. Ua ntej, martensite tsis soluble hauv chromium thiab molybdenum dua li austenite thiab ua rau chromium depleted thaj ua rau thaj ntawm theem ciam teb. Thib ob, martensite yog theem cathodic nrog rau kev hwm rau austenite, uas ua rau tsim cov galvanic microcells thiab anodic dissolution ntawm cov neeg nyob sib ze austenite. Potentiodynamic polarization scans hauv 100 ppm chloride tov ntawm 80℃qhia tias txias khoov 316 stainless hlau nrog 15% martensite muaj peev xwm pitting ntawm +150 mV vs Ag / AgCl, thaum tib cov khoom nyob rau hauv tag nrho recrystallised mob muaj pitting peev xwm ntawm +350 mV. Qhov kev hloov ntawm 200 mV txhais tau hais tias thaj av khoov xav tau tsawg dua anodic polarization los pib qhov pits.

Quantitative kev sib raug zoo ntawm lub vojvoog dabtsi yog khoov thiab lub neej pitting
U-zoo li tus 316 stainless hlau tso cua sov (thickness 1.5 mm, txoj kab uas hla 12 mm) tau raug tswj immersion thwmsim nyob rau hauv cov khoom cua txias (80 ppm Cl−, 200 ppm SO42−, pH 7.2, 85 degree) los ua kom pom qhov tsis ua hauj lwm ntawm cov cua sov ua haujlwm raws li kev ua haujlwm ntawm lub tshav kub 8 W/cm 2 . Kev ua tsis tiav tau txhais tau tias yog ib qho perforation vim pitting ntawm qhov khoov sab nraud apex.

Khoov vojvoog 36 hli (3D, strain≈3.3%): Nruab nrab pitting tsis ua hauj lwm tom qab 2100 h. Martensite cov ntsiab lus ntawm bent apex 6% Ntau qhov chaw pib, sluggish propagation.

Khoov vojvoog 24 mm (2D, strain 5.0%): Nruab nrab pitting tsis ua hauj lwm tom qab 1150 h Martensite cov ntsiab lus: 11% Pits nucleated nyiam ntawm tensile sab strain peaks.

Khoov vojvoog 18 mm (1.5D, strain 6.7%). Qhov nruab nrab pitting tsis ua haujlwm 550 teev. martensite cov ntsiab lus 18%; Localized corrosion nyob rau hauv lub nplhaib 2 hli ntawm sab nraud khoov.

Khoov vojvoog 12 hli (1D, lim 10%): nruab nrab pitting tsis ua hauj lwm tom qab 180 h. Martensitic cov ntsiab lus: 27%. Fast perforation nrog tawg hauv qee zaus.

Hauv cov ntawv thov uas muaj cov tshuaj chloride ntau dua (300-500 ppm) hauv cov txheej txheem dej pitting lifetime ntawm txhua lub vojvoog khoov raug txo los ntawm lwm qhov ntawm 2-3. Xwb, rau cov dej kub hauv qab 50 degree, lub martensite-induced pitting acceleration yog qhov tseem ceeb vim qhov tseem ceeb pitting kub yog siab tshaj qhov kub ua hauj lwm txawm rau khoov seem.

Thermal thiab mechanical teebmeem ntawm localized pitting ntawm khoov.
Cov qauv tsim uas tsom kev ntxhov siab ntawm lub vojvoog khoov ua rau qhov tsis ua haujlwm ntawm pitting tshwj xeeb yog teeb meem. Thaum lub qhov dej tawg los ntawm phab ntsa sheath, cov khoom cua sov sab hauv (feem ntau NiCr lossis FeCrAl hlau) raug rau cov txheej txheem kua. Hauv cov dej raws li cov txheej txheem no ua rau muaj kev txhaum hauv av tam sim ntawd thiab kaw lub tshuab cua sov. Txawm li cas los xij, cov chaw kub sib cais tsim nyob rau hauv ib nrab - qhov tuab tuab txawm tias ua ntej tag nrho cov perforation vim yog qhov siab dua thermal resistance thiab localized tam sim no ceev nyob rau hauv lub seem phab ntsa thickness ntawm lub qhov hauv paus. Infrared thermography ntawm lub rhaub nrog 30% phab ntsa nkag ntawm qhov khoov qhia qhov kub thiab txias nce ntawm 35-50℃tshaj qhov ntsuas kub ntawm qhov kub ntawm qhov khoov. Qhov chaw kub no ua rau muaj kev xeb thiab tuaj yeem ua rau kub hnyiab tau - tawm ntawm cov xov hlau sab hauv vim muaj cua sov hauv zos. Txawm nyob rau hauv cov tshuab pressurized, ib feem ntawm qhov tob tuaj yeem ua rau muaj kev ntxhov siab thiab ua rau qaug zog tawg thaum lub tshuab cua sov raug thermal cycling.

Lub tensile residual stresses induced los ntawm dabtsi yog khoov kuj ua rau kev nyuaj siab corrosion cracking (SSC) ntawm tej yam kev mob. Kev sib xyaw ua ke ntawm qhov seem tensile stress (feem ntau yog 100{2}}250 MPa ntawm khoov sab nrauv fiber ntau), martensite thiab kub nce ua rau muaj kev sib koom ua haujlwm tsis ua haujlwm hauv chloride- muaj cov xwm txheej rau 316 stainless hlau. Cov ntaub ntawv keeb kwm muaj rau cov tshuaj batch reactors, qhov twg U-zoo li tus 316 cua sov, khoov rau 1.5D radii nyob rau hauv 200 ppm Cl- kev pab cuam ntawm 95 degree, ua tsis tau tejyam nyob rau hauv transgranular SCC tom qab 300 teev, thaum zoo tib yam heaters bent rau 3D radii ua hauj lwm rau yuav luag 30 teev.

Khoov Radius Xaiv Phau Ntawv Qhia los ntawm Chloride Qib thiab Kev Ua Haujlwm Kub
Cov kev txiav txim siab hauv qab no matrix pab engineers hauv kev txhais qhov tsawg kawg nkaus khoov radii rau U-zoo li tus thiab kev cai- tsim 316 stainless hlau hluav taws xob cua sov raj. Rau txhua qhov sib xyaw ua ke ntawm cov tshuaj chloride concentration thiab qhov siab tshaj plaws hauv lub cev kub, qhov pom zoo tsawg kawg nkaus R / t piv (khoov vojvoog faib los ntawm lub raj sab nraud) yog muab los txwv kev txhim kho martensite kom tsawg dua 5%.

Maximum Chloride Concentration (ppm) Maximum Sheath Temperature (degree) Pom zoo Yam tsawg kawg nkaus Khoov Radius (ntau lub raj OD)Predicted Pitting-Lub Neej Dawb (teev) Koj Puas Xav Tau Tshaj Tawm- Khoov Kub Khoov?
< 50 < 60 2.0 D > 5000 No 50 – 100 < 60 2.0 D > 4000 No 50 – 100 60 – 90 2.5 D > 3000 No 50 – 100 90 – 110 3.0 D > 2000 Recommended (solution anneal if possible)
600 > 90 4.0 D > 600 Yuav tsum tau + xav txog kev hloov kho hlau (Incoloy 825) > 600 > 100 4.5 D > 500 Yuav tsum tau + xav txog kev hloov kho hlau (Incoloy 825) > 600 > 100 5.0 D > 400 Yuav tsum tau +{ xav txog kev hloov kho hlau (Incoloy 825 > D > 400) Yuav tsum tau + xav txog kev hloov kho hlau (Incoloy 825) > 600 > 100 7.0 D > 200 Yuav tsum tau + xav txog kev hloov kho hlau (Incoloy 825) > 600 > 100 8.0 D > 100 Yuav tsum tau + xav txog kev hloov kho hlau (Incoloy 825) 600 {{}} Qhov kub thiab txias Tsis txhob txias bends 100000 Siv 316 ncaj los yog txav mus rau cov hlau uas muaj zog dua
Rau daim ntawv thov uas yuav tsum tau compact U- khoov me dua 2.5D nyob rau hauv nruab nrab chloride tej yam kev mob, manufacturers tej zaum yuav xaiv los siv ib tug ncej- khoov tshuaj annealing txheej txheem, cua sov rau 1050℃tom qab dej ceev quenching, kom recrystallise lub strained qauv thiab tshem tawm martensite. Txawm li cas los xij, kev daws teeb meem-annealing ntawm ua tiav cov cua sov sib sau ua ke feem ntau tsis tuaj yeem ua tau vim tias cov cua sov sab hauv thiab cov ntsaws ruaj ruaj tsis tuaj yeem zam cov kub no. Nyob rau hauv cov xwm txheej no, cov lus teb ua tau zoo yuav yog los qhia lub vojvoog khoov loj dua lossis ntau dua, tab sis tseem corrosion-tiv taus, alloy xws li 316Ti (uas muaj titanium ntxiv rau kev ruaj khov ntawm carbides thiab tsis tshua muaj siab tsim martensite).

Cov kauj ruam ntxiv los txo kev khoov -Txog Corrosion
Thaum tsim cov kev txwv yuav tsum tau nqaim khoov vojvoog ntawm 316 stainless hlau sheath, peb txoj kev ua haujlwm tuaj yeem rov ua kom muaj kev tiv thaiv corrosion. Cov kab mob hauv cov fiber ntau yog proportional rau t / R. Yog li, qhov tuab ntawm phab ntsa ntawm lub raj ua ntej khoov, qhov tsawg dua qhov sib txawv ntawm cov fiber ntau sab nraud rau qhov muab khoov vojvoog. Lub 1.8 hli phab ntsa raj khoov mus rau 1.5D lub vojvoog muaj qhov qis dua li 1.2 hli phab ntsa raj khoov rau tib lub vojvoog. Qhov no ua rau txo qis ntawm martensite ntau lawm nyob ib ncig ntawm 30%. Qhov thib ob, qhia txog cov pa roj carbon tsawg 316L (qhov siab tshaj 0.03% C) uas tsis yog 316 (0.08% C) yuav ua rau kom muaj zog tiv thaiv kev kub ntxhov thaum khoov thiab lwm yam vuam txuas ntxiv, tab sis yuav tsis ncaj qha tiv thaiv kev tsim martensite. Thib peb, tom qab- khoov electropolishing ua haujlwm tshem tawm cov txheej txheej nyias (20–50 µm) nrog qhov siab tshaj plaws ntawm martensite thiab deformation-vim qhov tsis zoo. Kev ntsuam xyuas hluav taws xob qhia tau hais tias electropolishing 1.5D khoov coj lub peev xwm pitting mus rau hauv 50 mV ntawm lub xeev tsis khoov, thiab nce lub neej kev pab cuam los ntawm qhov tseem ceeb ntawm peb ntawm qhov tsis sib xws.

Khoov Radii rau Heavy Duty 316 Stainless Steel Immersion Heaters
Cov kws tsim qauv thov cov lus hais ntawm U-zoo li tus lossis kev cai khoov 316 stainless hlau hluav taws xob cua sov cov raj yuav tsum qhia qhov tsawg kawg nkaus khoov vojvoog hauv ntau lub raj sab nraud, qhov xav tau chloride concentration thiab siab tshaj plaws ua haujlwm kub ntawm cov txheej txheem kua. Tsis txhob ntseeg tias cov chaw tsim khoom tus qauv khoov vojvoog yog OK rau koj cov dej chemistry (feem ntau yog 2D lossis 1.5D). Rau kev txhim kho tshiab nrog cov dej tawv thiab cov tshuaj chloride zoo ib yam ntawm cov khoom siv hauv nroog (50-150 ppm Cl-, 60-}80℃kev khiav hauj lwm kub) muab qhov tsawg kawg nkaus 3D khoov vojvoog kom paub tseeb tias martensite concentration qis dua 5% thiab kwv yees pitting {{17} ntau dua 10} xuab moos, lub neej dawb Yog tias qhov chaw txwv tsis pub hais khoov nruj dua li 2.5D, nug tus neeg muag khoom rau cov kab mob -induced martensite ntsuas (ferritescope los yog X-ray diffraction) ntawm cov qauv khoov, thiab xav txog electropolishing los yog cov txheej txheem tom qab khoov kev ntxhov siab. Los ntawm kev kho khoov lub vojvoog raws li qhov tsim qauv sib txawv ntawm qhov sib npaug ntawm cov phab ntsa tuab thiab qhov chaw polishing, cov txheej txheem engineers tuaj yeem tiv thaiv kev ua tsis tiav ntxov uas tsis yog los ntawm cov ntu ncaj, tab sis los ntawm qhov cuam tshuam sab nraud ntawm txhua qhov khoov.