Yuav Ua Li Cas Qhov Nruab Nrab ntawm Thawj TiN Inclusions hauv Nqus -Arc-Remelted (VAR) 316L Heater Sheath Tubing Tswj lub Pit Initiation Lub Sijhawm hauv Oxygenated High-Purity Dej ntawm 90 degree

Inclusion Stability nyob rau hauv lub Strongly Oxidising Conditions

The pitting resistance of 316L stainless steel sheathed electric heating tubes used in oxygenated high-purity water systems like auxiliary cooling systems of nuclear power plants, pharmaceutical water-for-injection (WFI) heaters or semiconductor ultrapure water (UPW) heaters containing dissolved oxygen of 2-8 ppm is controlled by titanium nitride (TiN) inclusions rather than manganese sulphide (MnS) or aluminium oxide (Al2O3). Under very oxidising conditions, the MnS inclusions are quickly oxidised and dissolved at a high oxygen potential and are thus harmless. Al₂O₃ inclusions are inert. TiN inclusions are semi-conducting however and galvanically cathodic to the 316L matrix. The cathodic reaction (reduction of oxygen) is effective on the TiN surface in oxygenated water generating a galvanic couple that causes the anodic dissolution of the surrounding matrix and therefore the pitting initiation. Even in VAR grade 316L (vacuum arc remelted, very low inclusion content), TiN volume fractions as low as 0.0005-0.001% (5-10 ppm Ti) can lead to pits after 5,000-10,000 hours at 90°C. Pit initiation times are >50,000 teev qis dua 0.0002% (2 ppm Ti). Tsab ntawv xov xwm no suav txog qhov sib txuas ntawm TiN suav nrog qhov ntim feem (tswj los ntawm titanium concentration) thiab lub sijhawm rau qhov pib pib hauv cov dej purity siab oxygen ntawm 90oC.

Mechanism of TiN-Induced Pitting in Oxygenated Water

TiN is a highly electrically conductive material with high electrochemical potential. In oxygenated water, the cathodic reaction (O2 + 2H2O + 4e- -->4OH-) tshwm sim zoo dua ntawm TiN qhov chaw vim tias lawv muaj cov pa oxygen txo qis dua qhov muaj peev xwm tshaj piv rau cov txheej txheem passive ntawm 316L. Localized dissolution ntawm qhov suav nrog- matrix interface yog tshwm sim los ntawm galvanic tam sim no ntawm TiN cathode thiab cov nyob sib ze 316L matrix (anode). Yog hais tias lub qhov me me pib, qhov kev txhoj puab heev hauv zos chemistry yuav ua rau nws loj hlob txawm tias TiN particle tawg. Lub sijhawm pib lub qhov dej yog qhov sib npaug ntawm TiN suav nrog qhov loj thiab qhov ntom. Rau TiN suav nrog Ti-6Al-4V (VAR 316L), qhov tseem ceeb suav nrog yog TiN (los ntawm cov seem Ti ua haujlwm ua deoxidiser lossis Ti muaj cov seem) nrog qhov loj feem ntau 1-5 μm.

Txheeb xyuas qhov kev sib raug zoo ntawm TiN ntim feem thiab lub sijhawm pib lub qhov

Lub sijhawm pib lub qhov dej hauv qab no tau tsim los ntawm kev tswj xyuas ntev -lub sij hawm immersion kev sim ntawm VAR 316L tubing nrog cov qib titanium sib txawv (thiab yog li TiN ntim feem) hauv oxygenated (5 ppm O2) siab- dej huv (1 uS/cm,<1 ppb Cl-, 90 C) for up to 50 000 hours.

Residual Titanium (ppm) TiN Volume Fraction (%)TiN Inclusion Density (per mm2, >1 µm) TiN Size Range (µm) Pit Initiation Lub Sijhawm ntawm 90℃(teev, 5 ppm O2) Qhov siab tshaj plaws tom qab 10,000h (µm) Pom zoo rau 90℃Oxygenated High-Purity Service<2 (Ti-free) <0.0002 <0.1 N/A >50,000 (tsis muaj nqi)<5 Best 2-5 0.0002-0.0005 0.1-0.5 1-2 30,000-50,000 5-15 Excellent 5-10 0.0005-0.001 0.5-2 1-3 15,000-30,000 15-30 Yes 10-20 0.001-0.002 2-5 2-4 8,000-15,000 30-50 Acceptable 20-30 0.002-0.003 5-10 2-5 5,000-8,000 50-80 Marginal 30-50 0.003-0.005 10-20 2-6 3,000-5,000 80-120 Not recommended 50-80 0.005-0.008 20-40 3-8 1,500-3,000 120-200 No >80 >0.008 >40 >5 <1,500 >200 Nr
Kev cuam tshuam ntawm cov pa oxygen nyob rau hauv TiN-Induced Pitting

Cov pa oxygen ntau dua ua rau cov txheej txheem cathodic ntawm TiN, txo lub sijhawm rau qhov pib.

Dissolved Oxygen (ppm) Pit Initiation Time at 10 ppm Ti (hrs)Pit Initiation Time (hours) at 30 ppm TiMaximum Ti for 10,000h Life at Given O_2 Level (ppm) 0.5 >50,000 15,000-25,000 50 1 35,000-50,000 10,000-15,000 40 2 25,000-35,000 8,000-12,{11}}, 000-20,{13}},000-8,000 20 8 10,000-15,000 4,000-6,{19}},000-12,000 3,000-5,{23}} Cov lus pom zoo rau Cov Cuab Yeej Siv Dej Siab Siab

Rau 316L encased heaters nyob rau hauv oxygenated dej zoo ntawm 90℃qhov pom zoo titanium txwv yog:

Kev Pabcuam Hom Dissolved Oxygen (ppm) Ti, ppm rau 10,000h Pit-Kev Ua Haujlwm Kev Ua Haujlwm Dawb Lub Neej Steelmaking
Pharmaceutical WFI (tsawg O2)<1 40 VAR (standard) ICP-MS for Ti Pharmaceutical WFI (high O2) 5-8 15 VAR (low Ti) ICP-MS for Ti Semiconductor UPW (high O2) 8-10 10 VAR (ultra-low Ti) GDMS analysis
Nuclear auxiliary cooling 2-5 25 VAR lossis ESR Supplier certification
General high purity industrial 2-5 30 AOD + low Ti Mill daim ntawv pov thawj
TiN Inclusion thiab Ti Content Verification

Cov neeg yuav khoom xav tau qhov tseeb TiN txwv muaj ob txoj kev pov thawj. Thawj yog tshuaj ntsuam xyuas ntawm titanium cov ntsiab lus los ntawm inductively coupled plasma mass spectrometry (ICP-MS) los yog glow discharge mass spectrometry (GDMS) Txais: Ti <10-15 ppm rau siab purity kev pab cuam. Qhov thib ob yog kev tshawb nrhiav metallographic los ntawm kev tshuaj ntsuam xyuas electron microscopy (SEM) ntawm 1,000-5,000 × ntawm polished cross-section, suav TiN inclusions (paub los ntawm morphology-angular, cubic, kub-daj nyob rau hauv backscattered electron hom). Txais:<1-5 inclusions TiN per mm2 greater than 2 µm.

Xaus: Ultra Low Ti Spec rau Oxygenated High Purity Dej rhaub

Cov txiaj ntsig tau pom tias pitting tshwm sim hauv 316L stainless hlau encased rhaub hauv cov pa oxygenated (5 ppm O2) siab - dej huv ntawm 90℃thaum TiN suav nrog qis li 0.0005-0.001% (5-10 ppm Ti). Rau Ti cov ntsiab lus hauv qab 2-3 ppm, lub sijhawm pib lub qhov dej loj dua 50,000 teev. Cov kws tsim khoom siv 316L sheaths rau cov kws kho mob WFI, semiconductor UPW lossis nuclear auxiliary cua sov yuav tsum qhia meej lub tshuab nqus tsev arc remelting (VAR) nrog qhov siab tshaj 10-15 ppm titanium concentration validated los ntawm ICP-MS lossis GDMS. (Ti tsis tswj, feem ntau 20-50 ppm) rau ib txwm 316L yuav pit nyob rau hauv oxygenated high purity dej nyob rau hauv 2-5 xyoo ntawm 90℃ua rau paug ntawm lub siab purity system. Cov txheej txheem tau muab rau ntawm no, sib piv cov ntim feem pua ​​​​ntawm TiN (los ntawm cov seem Ti) mus rau lub sijhawm pib lub qhov dej hauv cov dej oxygenated, ua rau cov neeg siv khoom kom paub meej ultra-low titanium 316L uas tiv taus cov kev cuam tshuam nrog cov pitting nyob rau hauv qhov xav tau tshaj plaws high-purity, high-oxygen nqis.