Raws li qhov tshwj xeeb Tensile Residual Stress Tus Nqi Uas 316 Stainless Steel Heater Sheath Hloov los ntawm Passive mus rau Crack Initiation hauv 500 ppm Chloride Dej ntawm 25℃Ambient Service

Kev Nyuaj Siab rau Chloride SCC ntawm Chav Kub

Nyob rau hauv cov ntaub ntawv ntawm 316 stainless hlau sheathed hluav taws xob cua sov raj nyob rau hauv chloride bearing dej ntawm ambient kub (25 degree) nyob rau hauv daim ntawv thov xws li unheated cia tso tsheb hlau luam, dej txias circulating systems los yog raws caij nyoog cov khoom, qhov kev pheej hmoo ntawm chloride kev nyuaj siab corrosion cracking (SCC) yog feem ntau suav hais tias tsawg, raws li SCC ntawm austenitic stainless hlau feem ntau yuav tsum tau siab tshaj 60 degree. Txawm li cas los xij, kev ua tsis tiav tom qab thiab kev sim hauv chav sim tau pom tias 316 tuaj yeem tawg ntawm 25℃hauv 500 ppm chloride dej nyob rau hauv qhov muaj qhov txaus tensile residual stress, tab sis qhov pib kev ntxhov siab ntau dua li qhov kub siab. Qhov tseem ceeb parameter yog cov residual tensile kev nyuab siab los ntawm kev tsim khoom (kos duab, dabtsi yog khoov, straightening) ntxiv rau cov kev ntxhov siab ntxiv. Ntawm 25 {deg}C, kev tawg tsis pom hauv qab qhov kev ntxhov siab ntawm qhov kev txiav txim ntawm 80-90% ntawm lub zog tawm los ntawm cov khoom siv (165-185 MPa rau annealed 316 nrog 205 MPa ntawm kev tawm dag zog). Yog tias qhov kev ntxhov siab tshaj qhov theem no, cov kab nrib pleb tshwm sim tom qab lub sijhawm ntev induction (6 hli mus rau 2 xyoos) thiab loj hlob qeeb, nrog kev ua tsis tiav tom qab 2-5 xyoos. Kab lus no muab chav sov SCC qhov pib ntawm 316 sheaths hauv 500 ppm chloride dej.

Lub Mechanism ntawm Tsawg-Tsub SCC

Peb cov xwm txheej yuav tsum tau ua rau SCC ntawm 316 stainless hlau hauv cov tshuaj chloride: ib qho kev cuam tshuam microstructure (feem ntau muaj qee qhov kev ua haujlwm txias), kev nyuaj siab tensile thiab chloride ions. Thaum qhov kub thiab txias (80{11}}150 degree) SCC yog vim muaj cov tshuaj chloride thauj sai, cov nqi rov qab qeeb qeeb thiab cov tshuaj lom neeg hnyav ntawm qhov tawg. Ntawm 25℃qhov ua kom lub zog rau SCC tsis yog xoom, tab sis cov kinetics qeeb qeeb. Qhov sib txawv tseem ceeb yog tias qhov kev ntxhov siab rau kev tawg tau nce ntau vim qhov kub thiab txias. Qhov no yog vim qhov nce hauv qhov tseem ceeb ntawm cov pob txha pob txha taub hau rau kev ua kom nquag plias, uas yuav tsum tau siv ntau dua kev ntxhov siab. Annealed 316 ntawm 25C hauv 500 ppm Cl- muaj qhov kev ntxhov siab txog li 165-185 MPa (80-90% tawm los). Txias-ua hauj lwm 316 tau qis dua qhov kev ntxhov siab vim cov khoom muaj zog ntau dua tab sis kuj muaj zog dislocation ceev thiab tej zaum qee qhov martensite uas ua raws li qhov chaw pib tawg.

25 degree, 500 ppm chloride txiav txim siab pib rau SCC

Cov kev sib raug zoo hauv qab no tau tsim los ntawm kev ntsuas qhov ntsuas tsis tu ncua ntawm 316 stainless hlau (U- khoov thiab C- ntiv nplhaib) hauv 500 ppm chloride dej (pH 7.0, aerated) ntawm 25℃txog li 24 lub hlis (17,520 teev).

Cov Khoom Siv Khoom Siv Lub Zog Yield Strength (0.2% Offset, MPa) 25℃SCC Threshold Stress nyob rau hauv 500 ppm Cl- (MPa)Threshold as % of Yield Time to Crack Initiation at Threshold +10% (teev) SCC Risk Rating – 25 degree
Tag nrho annealed (<5% cold work) 205 165-185 80-90% >10,000 Tsawg heev
Lub teeb txias ua haujlwm (10-15%) 280 200-230 70-80% 5,000-10,000 Tsawg
Kev ua haujlwm txias txias (15-20%) 350 230-260 65-75% 2,000-5,000 Nruab Nrab
Kev mob khaub thuas hnyav (20-25%) 420 250-280 60-70% 1,000-2,000 Siab
Extreme cold work (>25%) >480 <280 (absolute) <60% 500-1,000 Extreme
With residual stress >90% yield 205 >185 >90% 500-2,000 (nyob ntawm kev ntxhov siab) Siab
Chav tsev kub qhov pib ua haujlwm ntawm chloride concentration

Qhov kev ntxhov siab yuav txo qis nrog cov ntsiab lus chloride ntxiv. Kev ntxhov siab rau 25℃annealed 316 raws li kev ua haujlwm ntawm cov ntsiab lus chloride yog muab rau hauv cov lus hauv qab no.

Chloride Concentration (ppm) Threshold Stress rau SCC ntawm 25℃(MPa, annealed 316) Lub Sijhawm Ua Haujlwm Ua Haujlwm ntawm qhov pib +10% (teev) Pom zoo tsim txwv<100 >205 (no cracking at yield) >50,000 (tsis muaj kev phom sij) Unlimited
100-200 190-205 20,000-50,000 Tsawg heev.
200-500 175-190 10,000-20,000 Txais tau nrog kev tswj kev ntxhov siab
500-1000 160-175 5000-10000 Residual stress<70% yield needed 1000-2000 140-160 2000-5000Stress Relief Recommendations 2,000-5,000 110-140 1,000-2,000 316 Not recommended for continuous stress >5,000 <110 <1,000 316 Not recommended; upgrade alloy
Cov kev txwv ntawm cov kev ntxhov siab nyob rau hauv cov dej txias

Cov kev txwv siab tshaj qhov seem yog muab rau 316 sheathed heaters nyob rau hauv chloride -cov dej bearing (200 - 1,000 ppm) ntawm ambient kub (25℃).

Chloride concentration (ppm) Qhov siab tshaj qhov kev ntxhov siab (MPa) rau 10-xyoo lub neej Kev sib npaug ua haujlwm txias txwvPost-Forming Kev Kho Kom Zoo<200 <205 (full yield) Any None Required
200-500 <150 <25% cold work None for straight portions
200-500 <120 (at bends) <15% extra bend stressStress alleviation for tight bends ( R/D<3)
500-1,000 <120 <15% cold work Stress relief 400oC 1 hr
500-1,000 <100 (at bends) <10% extra strainFull solution anneal after bending >1,000 <80 <5% cold work (just annealed) Full solution anneal necessary
Field Detection ntawm SCC ntawm ambient kub

Rau 316 lub rhaub dej tsis ua haujlwm hauv 25℃chloride kev pabcuam (200-1,000 ppm Cl-), SCC cov kab nrib pleb yuav tshwm sim tom qab 1-3 xyoos ntawm kev siv tsis tu ncua lossis tsis sib xws. Cov pob txha pob txha yog transgranular (los ntawm cov nplej) thiab ceg, zoo li qhov kub siab SCC tab sis feem ntau luv dua thiab ntev dua. Cov pob txha pob txha tuaj yeem pom cov cim qhia ntawm kev ua kom tawg sai sai (paj cim) thiab cov khoom siv corrosion me me. Feem ntau lub hauv paus chiv keeb yog nyob rau hauv ib qho chaw ntawm cov kev ntxhov siab tseem ceeb: sab nraud ntawm lub voj voog ntawm txoj kab nkhaus, ib qho chaw txias txias nrog kev txo qis los yog qhov chaw vuam kub. Thaum ib ntu ua tsis tiav yog ntsuas rau qhov kev ntxhov siab los ntawm X-ray diffraction qhov tseem ceeb feem ntau tshaj 150-180 MPa. Rau cov kev ua tsis tau zoo li no, cov lus teb yog xav kom muaj kev ntxhov siab tom qab khoov (400℃rau 1 teev) rau kev yuav khoom yav tom ntej, txo qis kev ntxhov siab rau hauv qab 100 MPa.

Tshwj xeeb Case: Sib Nqus Sib Nqus Sib Nqus Txhaum

Kev cuam tshuam tsis sib xws (kev ua kom qhuav) ntawm chav tsev kub, cov ntsiab lus chloride nce thaum ziab ua rau kom nrawm SCC tsim. Cov dej ntau yuav tsuas pom 500 ppm chloride. Txawm li cas los xij, lub tshuab cua sov uas tau tso cai kom qhuav ib ntus tuaj yeem muaj cov tshuaj chloride ntau ntawm 5,000-10,000 ppm ntawm cov kav dej yog li txo qhov kev ntxhov siab. Rau kev pabcuam tsis sib xws, qhov kev tso cai ntawm qhov kev ntxhov siab yuav tsum yog ib nrab ntawm qhov ntawd rau kev nkag mus tas li.

Xaus: Residual Stress Control rau Ambient Chloride Service

SCC nyob rau hauv 316 stainless hlau encased heaters nyob rau hauv 500 ppm chloride dej ntawm 25℃tau pom tshwm sim thaum lub tensile residual kev nyuaj siab nyob rau hauv ntau tshaj li ntawm 165-185 MPa (80-90% ntawm yield rau annealed khoom). Qhov chaw pib rau qhov no yog qhov siab, tab sis cov kev ntxhov siab hauv zos los ntawm kev ua haujlwm txias (khoov, kos duab thiab lwm yam) tuaj yeem muaj ntau dua 200-300 MPa, txaus los ua kom tawg ntawm chav tsev kub tom qab 1-3 xyoos. Rau kev ua haujlwm hauv chlorides ntawm chav tsev kub, cov kws ua haujlwm xaiv 316 sheaths yuav tsum xav txog kev txo qis kev ntxhov siab tom qab (400-450 degree, 1 teev) kom txo qis kev ntxhov siab thaum cov tshuaj chloride ntau tshaj 500 ppm lossis thaum khoov nruj dua R / D=3. Rau cov tshuaj chloride ntau dua 1,000℃ppm. Duplex 2205 tau pom zoo. Txoj hauv kev uas tau hais los ntawm no txuas cov kev ntxhov siab nyob rau hauv qhov ntsuas qhov ntsuas SCC nyob rau hauv chav tsev kub, ua rau cov neeg yuav khoom xaj 316 sheaths uas tiv thaiv cov tshuaj chloride tawg txawm tias tsis muaj kev pabcuam.