Yuav Ua Li Cas Cov Qhov Ncauj Ntawm Cov Tsis-Metallic Oxide Inclusions Tom Qab Nqus Arc Remelting ntawm 316 Heater Sheath Tubing Control Pit Initiation Site Density nyob rau hauv siab -Purity Dej ntawm 90 degree

Cov pej xeem suav nrog tsuas yog Pitting Initiation Mechanism hauv qis -Chloride Ib puag ncig

With 316 stainless steel clad electric heating tubes in high purity water applications such as pharmaceutical water systems, semiconductor rinse tanks or high pressure boiler feedwater when the chloride levels are under 10 ppm, conventional chloride-induced pitting is not expected. However the pitting does occur in these conditions and the beginning sites are virtually solely non-metallic oxide inclusions (mainly alumina, Al2O3 and spinels) rather than manganese sulphides. The oxide inclusion volume fraction of a normal electric-arc furnace (EAF) 316 is usually 0.01–0.05%. Vacuum arc remelting (VAR) or electroslag remelting (ESR) reduce the oxide inclusion volume percentage to less than 0.002% (a 10-25 fold reduction). A 316 sheath with an oxide inclusion volume fraction >0.01% hauv dej purity siab ntawm 90℃yuav tsim 10-50 pits / cm2 nyob rau hauv 1,000 teev, tab sis VAR kho cov ntaub ntawv nrog<0.002% inclusions is pit-free for >10,000 teev. In this paper, the influence of service life, pit initiation density and oxide inclusion volume fraction on the high-purity water was investigated.

Pitting tus cwj pwm ntawm steel induced los ntawm oxide inclusion mechanism

Nyob rau hauv sib piv rau manganese sulfide inclusions uas yog electrochemically active thiab induce pitting los ntawm dissolution, oxide inclusions (Al₂O₃, MgO·Al₂O₃) yog inert insulators. Lawv ua si lub luag hauj lwm mechanical thiab geometric hauv qhov pib ntawm pitting. Qhov sib txuas ntawm oxide suav nrog thiab austenitic matrix sib txawv hauv coefficient ntawm thermal expansion (CTE ntawm Al2O3=8 × 10−6 /℃vs . 316 ≈ 17 × 10−6 /℃). Qhov kev tsis sib haum xeeb ntawm CTE no ua rau muaj qhov sib txawv (crevice) ntawm kev suav nrog thiab matrix thaum cua sov (txog 90 degree) thiab cua txias. Qhov no crevice yog ntim nrog dej thiab chloride ions (txawm tias ntawm<10 ppm) and constitutes the differential aeration cell that causes pitting. The pit then propagates by normal chloride driven mechanisms, but the bulk chloride is low. The number of pits is related to the number of oxide inclusions exposed at the surface.

Kev sib raug zoo ntawm oxide suav nrog ntim feem thiab qhov ntom ntom ntom ntawm 90 degree

Kev tswj immersion tests ntawm 316 tubing los ntawm ntau cov txheej txheem steel ntau lawm (EAF, AOD, VAR) nyob rau hauv cov dej purity siab (8 ppm Cl⁻, 15 µS / cm conductivity, pH 7.0) ntawm 90℃rau 5,000 teev tau tsim cov hauv qab no qhov pib qhov ntom ntom.

Ib txwm Oxide Inclusion Volume Fraction (%) hauv Steelmaking ProcessSize Range of Inclusions (µm) Pits / cm² tom qab 5,000 teev ntawm 90℃Qhov siab tshaj plaws qhov tob tom qab 5,000 h (µm) Lub Sijhawm rau thawj qhov chaw ruaj khov (h) Pom Zoo Kev Pabcuam rau Cov Dej Purity Siab
VAR (nqus arc remelted)<0.002 1-5 <0.1 <10 >10,000 ESR Zoo Tshaj Plaws (electroslag remelted) 0.002-0.005 1-8 0.1-0.5 10-20 5,000-10,000 Zoo heev AOD (argon-oxygen decarburized) 0.005-0.010 2-10 0.5-2 20-40 2,000-5,000 Txais
AOD + calcium kev kho mob 0.008-0.015 3-15 2-5 30-60 1,000-3,000 Marginal
EAF (hluav taws xob arc rauv, qauv) 0.015-0.030 5-25 5-20 50-100 500-1,500Tsis pom zoo
EAF (zoo tsis zoo) 0.030-0.050 10-50 20-50 80-150 200-500 Tsis tau
Kev cuam tshuam ntawm chloride Concentration ntawm kev suav nrog-Induced Pitting Threshold

Pitting pib ntawm oxide inclusions yog nrawm los ntawm qhov muaj cov chloride tsawg tsawg. Cov lus hauv qab no qhia txog qhov siab tshaj plaws tso cai oxide suav nrog feem pua ​​​​ntawm 5 xyoo kev pabcuam raws li kev ua haujlwm ntawm chloride concentration ntawm 90 degree.

Chloride Concentration (ppm) Maximum Permissible Oxide Inclusion Volume Fraction (%) Npaj Txoj Kev Steelmaking Alternate yog Overrun<1 0.020 AOD or betterNone 1-5 0.010 AOD + calcium therapyNone 5-10 0.005 AOD (premium) or ESR None 10-20 0.003 ESR or VAR 316L with electropolishing 
20-50 0.002 VARUpgrade rau 316L, passivation50<0.001 VAR + surface removal 316 not recommended for long life
316 Inclusion-Controlled Specification for High Purity Water Service

Cov lus qhia tshwj xeeb rau 316 sheathed heaters rau siab - kev siv dej huv hauv cov ntaub ntawv yuav khoom yuav tsum muaj cov hauv qab no:

Daim ntawv thov Maximum chloride (ppm) Steelmaking txheej txheem yuav tsum tau Muaj ntau tshaj plaws oxide inclusion ntim feem Txoj kev tshawb xyuas
Pharmaceutical WFI (dej rau txhaj tshuaj)<3 VAR or ESR <0.003% (30 ppm) ASTM E45 + SEM/EDS
Semiconductor yaug (ultrapure)<1 VAR <0.002% (20 ppm) SEM/EDS of 10 fields 
Siab -siab boiler pub dej<5 ESR or AOD premium <0.005% (50 ppm) ASTM E45 Method A General high purity industrial <10 AOD with calcium treatment <0.010% (100 ppm) ASTM E45

Cov neeg yuav khoom xav tau kev tswj hwm 316 muaj peb txoj hauv kev pov thawj. Thawj yog ASTM E45 (Txoj Kev Xeem Txuj Ci rau Kev Txiav Txim Cov Ntsiab Lus Ntawm Cov Hlau), Txoj Kev A (qhov phem tshaj plaws) lossis Txoj Kev D ( duab tsom xam). Rau siab purity daim ntawv thov qhov siab tshaj plaws ntawm 0.5 yog teev rau hom B (alumina) suav nrog. Qhov thib ob yog scanning electron microscopy (SEM) nrog lub zog dispersive X-ray spectroscopy (EDS) ntawm tus ntoo khaub lig polished-section (500-1,000 ×) suav suav nrog hauv 10 thaj chaw saib. Kev lees txais qhov pib tsawg dua 10 suav nrog ib mm 2 siab dua 2 µm. Qhov kev sim thib peb yog qhov simplified immersion sim qhov twg cov qauv ntawm cov raj yog raus hauv dej purity siab (10 ppm Cl⁻) ntawm 90℃rau 1,000 teev. Yog tias cov pits pom, cov ntsiab lus suav nrog yog siab dhau.

Field Identification of Pitting los ntawm Oxide Inclusions

Oxide inclusions yog qhov yuav ua rau 316 lub rhaub dej kub hauv cov dej zoo uas cov chlorides tsawg dua 10-20 ppm. Microscopically (200{14}}500 ×) qhov chaw qhov chaw yuav nthuav tawm Al 2 O 3 lossis spinel suav nrog ntawm lub plawv ntawm lub qhov, qhov kev suav feem ntau raug tshem tawm ib nrab. Cov pits yog me me (inch 10-100 µm), ntau thiab sib npaug. Kev kuaj EDS ntawm lub qhov chaw pov thawj O thiab Al. Kev kho rau cov teeb meem no yog qhia VAR lossis ESR-qib 316 rau kev yuav khoom yav tom ntej. Lub tshuab cua sov tsis tuaj yeem kho tau thiab yuav tsum tau hloov nrog cov kav dej sib txuas.

Xaus: Kev Tsim Nyog ntawm VAR/ESR 316 rau Kev Pabcuam Siab Purity Dej

Rau 316 stainless hlau qhwv cov cua sov hauv cov dej purity siab (chlorides<10 ppm) at 90°C, the dominant pitting initiation mechanism is galvanic crevice attack at non-metallic oxide inclusions. Standard EAF steel with 0.015-0.03% oxide inclusion volume fractions produces 5-20 pits/cm2 and perforation in 2-5 years in 5,000 hours. VAR or ESR processing decreases the oxide inclusion volume percentage to <0.002-0.005% and increases the pit-free life to >10,000 teev. Yog tias 316 sheaths tau teev tseg rau kev siv tshuaj, semiconductor lossis ultra- daim ntawv thov cua sov dej ntshiab, ces cov engineers yuav tsum xav tau VAR lossis ESR cov khoom siv qib thiab ntsuas cov ntsiab lus suav nrog rau ASTM E45 nrog kev txwv hnyav.<0.5 for Type B inclusions. The framework described correlates oxide inclusion volume percentage with measurable pit initiation density and service life. Buyers may now select 316 tubing that resists pitting even in the most aggressive high purity water situations.