Yuav ua li cas cov residual Stress Profile los ntawm Tube Straightening ntawm 316 Stainless Steel Heater Sheaths Hloov qhov pib rau chloride Stress Corrosion Cracking

Unintended qhov chaw: Tensile nto kev nyuaj siab los ntawm cov txheej txheem straightening.

Roller straightening feem ntau yog cov kauj ruam kawg hauv kev tsim khoom rau 316 stainless hlau sheathed hluav taws xob cua sov raj ua ntej lawv raug txiav kom ntev thiab khoov. Cov txheej txheem no tshem tawm curvature ntawm lub li -kos (los yog raws li -annealed) raj los ntawm kev khiav nws los ntawm offset rollers, thiab qhia txog qhov nyuaj residual stress profile mus rau lub raj nto. Tensile residual stresses ntawm 50-200 MPa yog qhia nyob rau hauv lub sab nrauv 50-150 µm ntawm lub sheath phab ntsa ntawm qhov nro ntawm txhua straightening roller contact point. Cov residual tensile stresses ua rau muaj kev ntxhov siab los ntawm thermal expansion thiab sab hauv siab nyob rau hauv chloride-muaj ib puag ncig ntawm qhov kub siab (siab tshaj 60 degree) kom induce stress corrosion cracking (SCC) at stresses that will be safe for stress-relieved material. Daim ntawv no ntsuas qhov kev sib raug zoo ntawm qhov kev ntxhov siab vim qhov ncaj, qib chloride thiab lub sij hawm pib ntawm SCC, thiab muab cov kev txwv tshwj xeeb rau kev txo kev ntxhov siab tom qab straightening hauv kev pabcuam corrosive.

Mechanism ntawm qhov kev nyuaj siab ntawm qhov chaw inducing straightening

Stainless hlau tubing yog cov menyuam ncaj nraim los ntawm kev hla ntawm cov txheej txheem offset rollers uas plastically deform lub raj hauv lwm cov lus qhia. Lub tensile hom nyob rau hauv cov txheej fibers ntawm lub raj feem ntau yog li ntawm 0.5% mus rau 2.0% nyob ntawm qhov pib curvature thiab lub straightening roller offset. Ib tug imposed tensile yas hom ntawm 0.5% nyob rau hauv annealed 316 stainless hlau, muaj ib tug yield zog ntawm roughly 205 MPa, sib raug mus rau ib tug residual kev nyuaj siab ntawm 150-200 MPa (75-100% yield zog). Kev faib tawm ntawm cov kev ntxhov siab nyob hauv ib cheeb tsam: qhov kev ntxhov siab loj tshaj plaws yog pom nyob rau hauv ib txheej txheej nyias (20-100 µm sib sib zog nqus) vim hais tias qhov ncaj deformation feem ntau elastic ntawm lub raj tub ntxhais thiab cov yas tsuas yog ntawm qhov chaw. Cov kab nrib pleb nucleate ntawm qhov chaw thiab loj hlob mus rau hauv qhov seem seem kev ntxhov siab. Cov txheej nyias nyias no zoo meej rau SCC pib. Feem ntau, cov kev taw qhia ntawm residual stresses yog axial (raws li qhov ntev ntawm lub raj) rau ntawm qhov chaw ntawm lub raj nyob rau hauv kev sib cuag nrog cov chais, nrog ib ncig ntawm cov kev ntxhov siab nyob rau hauv cov npoo ntawm cov menyuam sib cuag. Axial residual stresses yog teeb meem tshwj xeeb tshaj yog rau cov cua sov sheath vim hais tias lawv nyob rau hauv tib txoj kev raws li lub hoop kev nyuaj siab tshwm sim los ntawm lub sab hauv siab, ob qho tag nrho cov kev nyuaj siab mus txog rau ib tug net tensile kev nyuaj siab uas accelerates kev loj hlob puas.

Kev txo qis ntawm SCC qhov pib vim muaj kev cuam tshuam ncaj qha

Kev ntsuam xyuas ntawm 316 tubing hauv boiling magnesium chloride (154 degree, standardized SCC test) qhia tau hais tias ncaj tubing yam tsis muaj ncej-txoj kev ntxhov siab txo qis hauv 20-50 teev nyob rau hauv kev siv zog ntawm 200 MPa. Tib lub raj hauv qhov kev ntxhov siab txo qis (kev ntxhov siab nyob hauv qab 30 MPa) muaj sia nyob tshaj 500 teev. Nyob rau hauv qhov kev pab cuam muaj feem xyuam rau immersion heaters - 90℃dej nrog 1,000 ppm chloride - qhov tshwm sim yog qhov tseem ceeb . 316 sheaths nrog kev ntxhov siab alleviated tiv taus 1,000 ppm chloride rau 5-8 xyoo tsis muaj SCC. Ncaj nraim sheaths nrog residual nto strains ntau tshaj 150 MPa yuav tsim SCC puas nyob rau hauv 12-24 lub hlis ntawm tib theem ntawm chloride. Sheaths nyob rau hauv kev ntxhov siab yuav nyob mus ib txhis ntawm 500 ppm chloride. Straightened sheaths yuav tawg nyob rau hauv 3-5 xyoo. Qhov tseem ceeb ntawm kev sib xyaw ua ke rau SCC pib yam tsis muaj kev thov ncaj nraim yog 60℃thiab 300 ppm chloride. Tshaj 80 degree, kev sib xyaw ua ke ntawm cov tshuaj chloride siab tshaj 200 ppm nrog ncaj qha residual stresses tshaj 100 MPa yuav kawg ua rau SCC. Cov lus hauv qab no qhia lub sijhawm rau SCC pib ua haujlwm ntawm qhov seem ntawm qhov nro, chloride concentration thiab kub.

Residual Surface Stress from Straightening (MPa) Chloride Concentration (ppm) Sheath Temperature (degree) Time to SCC Crack Initiation (teev teev ua haujlwm) Lub Sijhawm rau Perforation (1.5 hli phab ntsa) Pom Zoo Ua Haujlwm<30 (stress relieved) 1000 90 >70,000 (>8 years) >80,000 Txais<30 (stress relieved) 2000 80 >50,000 >60,000 Txais tau nrog kev saib xyuas 50-100 (mob straightening) 500 90 20,000-30,000 (2.5-3.5 xyoo) 25,000-40,000 Marginal; Kev ntxhov siab tau pom zoo
50-100 (tshaj me ntsis) 1000 80 15,000-20,000 (1.7-2.3 xyoos) 18,000-25,000 Tsis pom zoo rau kev siv txuas ntxiv 100-150 (nruab nrab straightening) 300 90 10,000-15,000 (7 xyoo)-25,000 (1.101. Tsis kam txais siab tshaj 80℃100-150 (nruab nrab straightening) 500 80 8,000-12,000 (0.9-1.4 xyoo) 10,000-15,000 Tsis tau
150-200 (hloov ncaj) 200 90 3,000-6,000 (4-8 lub hlis) 4,000-8,000 Tsis kam txais cov tshuaj chloride
150-200 (hloov ncaj qha) 500 70 5,000-10,000 (7-14 lub hlis) 6,000-12,000 Hloov nrog cov raj txo kev ntxhov siab
Kev Tshawb Nrhiav thiab Kev Kho Kom Zoo Ntawm Cov Kev Nyuaj Siab ntawm Kev Ncaj Ncees

Cov neeg yuav khoom hais txog 316 lub tshuab cua sov rau kev siv tshuaj chloride muaj peb txoj hauv kev los xyuas qhov seem ntawm kev ntxhov siab los ntawm kev ncaj. Thawj yog ASTM G38 tus qauv kev coj ua rau kev tsim cov U- khoov cov qauv. Ib feem ntawm qhov raws li - tau txais tubing yog khoov 180o hla lub mandrel thiab muab tso rau hauv boiling magnesium chloride. Yog tias tawg tau tshwm sim nyob rau hauv 100 teev, qhov seem ntawm qhov nro ntawm kev ncaj yog txaus los ua rau SCC yam tsis muaj kev ntxhov siab. Cov txheej txheem thib ob yog X-ray diffraction (XRD) nrhiav kom pom cov kev ntxhov siab nyob rau ntawm lub raj. Qhov tseem ceeb tshaj 100 MPa qhia tias txo kev ntxhov siab tom qab kev kho kom ncaj. Txoj kev thib peb thiab yooj yim tshaj plaws yog qhov ua li ntawd -hu ua "ferroxyl test" (tooj liab sulphate-sulphuric acid etching) uas qhia tau hais tias thaj chaw ntawm cov kev ntxhov siab tseem ceeb li cov qauv tsaus nti. Residual strains hauv qab 30 MPa rau cov cua sov uas npaj rau kev pab saum toj no 70℃nrog chlorides siab tshaj 200 ppm yog tau los ntawm post- straightening stress relief anneal ntawm 400-500℃rau 1-2 teev. Tag nrho cov tshuaj annealing (1040 degree) tshem tawm tag nrho cov residual tensions tab sis tej zaum yuav ua rau distortion ntawm tubing thiab feem ntau tsuas yog teev rau cov kev siv tseem ceeb. Cov neeg yuav khoom tuaj yeem xav tau kev pov thawj ntawm kev ntxhov siab ua los ntawm tus neeg xa khoom tubing tom qab ncaj, (lossis qhov kev ncaj ncaj tsis ua tiav ntawm cov tubing annealed) uas muab kev ruaj ntseg zoo.

Kev txheeb xyuas hauv thaj tsam ntawm SCC los ntawm residuals ntawm straightening

Qhov ua rau ntawm cov khoom seem ncaj nraim yog qhov txawv ntawm cov duab ntawm cov kab nrib pleb thaum lub tshuab cua sov tsis ua haujlwm los ntawm SCC. Cov kab nrib pleb feem ntau tshwm sim hauv ntu ncaj ntawm cov ntaub qhwv, tsis yog khoov lossis welds, los ntawm kev ntxhov siab tsim los ntawm kev ncaj. Lawv feem ntau yog longitudinal (piv txwv li thaum uas tig mus rau lub raj axis) thiab tuaj yeem tshwm sim nyob rau hauv ib tug xov tooj ntawm parallel kab sib cais los ntawm 5-15 hli, sib xws rau cov menyuam sib cuag qauv. Cov pob txha tawg yog transgranular (hla ciam teb) rau 316 nyob rau hauv chloride ib puag ncig saum 80 C nyob rau hauv magnification nrog SCC raug branching. Fracture nto yog tsis ductile heev. Yog hais tias lub rhaub tsis ua hauj lwm yog los ntawm ib pawg uas tsis muaj kev ntxhov siab eased tom qab straightening, thiab cov kev pab cuam muaj xws li chlorides saum 300 ppm ntawm qhov kub siab tshaj 70 degree, qhov tseem ceeb ua rau tej zaum yuav residual stress generated los ntawm straightening. Tag nrho cov tso cua sov yuav tsum tau muab tshem tawm los ntawm kev pabcuam lossis hloov kho nrog kev kho kev ntxhov siab thaum ua tau rau cov kev teeb tsa no.

Cov ntsiab lus: txhais ntawm Residual Stress Control rau Chloride Service

Cov residual stress profile nkag mus rau hauv 316 stainless hlau tubing tom qab cov menyuam straightening yog ib qho txawv txawv uas yuav txo tau cov tshuaj chloride SCC qhov pib los ntawm ib yam ntawm 3 mus rau 5. Kub chloride ib puag ncig yuav tawg raj nrog nto residual strains saum toj no 100 MPa nyob rau hauv 1-2 xyoo nyob rau hauv tej chaw thaum stress alleviated-1 xyoo tubing. Rau ib qho kev pabcuam uas muaj cov tshuaj chlorides siab tshaj 200 ppm thiab kub siab tshaj 70 degree, engineers qhia 316 sheathed heaters yuav tsum xav tau ib qho ntawm cov hauv qab no: post-straightening stress relief (400-500℃for 1-2 hours), los yog ntawv pov thawj tias cov tubing tau straightened nyob rau hauv tag nrho annealed mob teem rau cov menyuam tawm kev ntxhov siab. Cov txheej txheem thov tuaj yeem siv los tiv thaiv kev ua tsis tiav thaum ntxov, uas feem ntau raug ntaus nqi rau "cov ntaub ntawv zoo", tab sis yog, qhov tseeb, vim tias tsis muaj kev tswj hwm qhov kev ntxhov siab cuam tshuam nrog txoj hlua ncaj, los ntawm kev hais txog cov txheej txheem ncaj rau ntsuas SCC pib lub sij hawm.