Yuav Ua Li Cas Lub Hwj Chim Loj ntawm Thawj Nb (C, N) Carbonitrides los ntawm Residual Titanium (0.02-0.08%) nyob rau hauv 347 Heater Sheath Tswj Pitting Initiation Site Ceev nyob rau hauv Chlorinated Seawater ntawm 35℃nrog 1.5 ppm Dawb Chlorine

Cov Me Me Alloying Element uas dhau los ua qhov tseem ceeb Pitting Initiator nyob rau hauv Oxidising Conditions

Hom 347 stainless hlau (Nb-stabilized) sheathed hluav taws xob cua sov raj raug chlorinated seawater (1.5 ppm dawb chlorine, 20,000 ppm Cl-) ntawm 35℃, raws li siv nyob rau hauv ntug dej hiav txwv fais fab nroj tsuag cua txias tshuab, desalination preheaters nrog reheaters los yog desalination preheaters. (0.02-0.08 wt%) los ntawm steelmaking (titanium-deoxidized seem lossis txhob txwm ntxiv). Primary titanium-nplua nuj niobium carbonitrides (Nb, Ti) (C, N) daim ntawv. Cov carbonitrides nyuaj no muaj ntau cathodic thiab ruaj khov dua li NbC ntshiab, yog li lawv yog cov chaw pib ua haujlwm zoo heev nyob rau hauv siab oxidising peev xwm ntawm chlorinated seawater. Rau qib titanium<0.01% primary carbonitride volume fraction <0.01-0.02 %, pit density <0.5 pits/cm² and service life >10 xyoo. Raws li cov ntsiab lus titanium nce los ntawm 0.03 mus rau 0.05%, qhov ntim feem ntawm carbonitride nce los ntawm 0.04 mus rau 0.08%, qhov ntom ntom ntawm 2 mus rau 5 pits / cm² thiab lub neej ntev ntawm 5 mus rau 7 xyoo. Ntawm titanium theem ntawm 0.06-0.08% qhov ntim feem yog 0.10-0.15% thiab qhov ntom ntom yog tshaj 10-20 pits / cm² thiab perforation yuav siv sij hawm qhov chaw nyob rau hauv 2-3 xyoo. Tsab ntawv xov xwm no qhia txog qhov sib txuas ntawm cov titanium residual concentration, thawj carbonitride ntim feem pua, qhov pib qhov ceev thiab kev pab lub neej nyob rau hauv chlorinated ntsev.

Mechanism ntawm Titanium Enhanced Pittingch Initiation

Titanium muaj kev sib raug zoo rau carbon thiab nitrogen ntau dua li niobium. Hauv 347 steelmaking, titanium (txog 0.02-0.08%) nyiam tsim titanium-nplua nuj carbonitrides (Ti(C,N)) uas tuaj yeem muaj niobium (Nb, Ti)(C, N). Cov khoom no yog tsim los ntawm qhov kub thiab txias thaum lub sij hawm solidification thiab loj (3-10 µm) thiab ruaj khov dua NbC ntshiab. Hauv cov dej hiav txwv chlorinated (muaj peev xwm oxidation siab los ntawm Cl2) cov txheej txheem cathodic (oxygen txo + chlorine txo) yog qhov tshwj xeeb ntawm cov carbonitride qhov chaw, yog li ua kom muaj zog galvanic ob peb nrog ib puag ncig austenitic matrix. Fast anodic dissolution yog induced los ntawm siab cathodic tam sim no ceev. Qhov siab chloride concentration ua rau qhov pib nrawm nrawm thiab nthuav tawm.

Quantitative Relation ntawm Titanium Cov ntsiab lus, Volume Fraction ntawm Carbonitride thiab Pitting Ceev

Cov hauv qab no qhov pib qhov ntom ntom thiab lub sijhawm perforation tau tsim rau 347 tubing nrog cov khoom seem titanium sib txawv (ntxuas niobium 0.40%, carbon 0.05%, nitrogen 0.04%) hauv chlorinated hluavtaws seawater (1.5 ppm dawb Cl 2 , 20,000 ppm) ntawm ppm. 5,000 teev.

Titanium (wt%) Volume Fraction of Primary (Nb,Ti)(C,N) (%) Carbonitride Particle Size (µm) Particle Morphology Pit Density after 5,000h (pits/cm²) Maximum Pit Depth tom qab 5,000h (µm) Lub Sijhawm rau Perforation (1.5 hli) Seawater degree<0.005 (Ti-free) <0.01 <1 None/rare <0.1 <10 >15 Best 0.005-0.010 0.01-0.02 1-2 Isolated 0.2-0.5 10-20 10-15 Yes 0.010-0.020 0.02-0.03 1-3 Scattered 0.5-1.0 15-30 8-12 Acceptable 0.020-0.030 0.03-0.05 2-4 Moderate 1-3 25-45 5-8 Marginal 0.030-0.040 0.05-0.07 2-5 Frequent 2-5 35-60 4-6 Not recommended 0.040-0.050 0.07-0.09 3-6 Numerous 4-8 50-80 3-4 No 0.050-0.060 0.09-0.12 3-8 Extensive 8-15 60-100 2-3 No 0.060-0.080 0.12-0.16 4-10 High density 15-30 80-130 1.5-2 No >0.080 >0.16 >5 Very high >30 >130 <1.5 No
Ntawm Kev Sib Tham Ntawm Ti thiab Nb ntawm Kev Tsim Cov Carbonitride

Cov niobium siab dua tuaj yeem them qee qhov kev cuam tshuam tsis zoo ntawm titanium los ntawm kev nyiam ua NbC tab sis titanium tseem muab faib rau carbonitrides.

Titanium (wt%) Niobium (wt%) Carbonitride Composition Pit Density (pits/cm2) Pom zoo rau Chlorinated Seawater 0.02 0.35 Ti-nplua nuj (Ti,Nb)(C,N) 2-4 Marginal 0.02 0.45 Ntau Nb-nplua nuj Nb{17}} nplua nuj 1-C2 0.5-1 Yog 0.05 0.35 Ti+Nb tov 8-12 Tsis yog 0.05 0.50 Ti+Nb tov 4-6 Tsis pom zoo 0.05 0.65 Ntau Nb-nplua nuj, qee qhov Ti 2-4 Marginal
Cov lus pom zoo rau 347 hauv Hiav Txwv Dej Chlorine

Rau 347 sheathed heaters hauv chlorinated ntsev ntawm 35 degree, cov kev txwv hauv qab no ntawm titanium thiab niobium txo qis pitting vim yog carbonitride tsim.

Desired Service Life @ 35C (years) Maximum Titanium (wt%) Minimum Niobium (wt%) Recommended Combined Limit Alternate Alloy >10 <0.01 0.45 Ti+Nb not applicable 347 acceptable 8-10 <0.02 0.50 Upgrade to 316L or duplex
5-8 <0.03 0.55 347 not recommended Duplex 2205 3-5 <0.04Not effective 347 unsuitable Duplex 2205 or titanium <3 >0.04 Tsis zoo 347 tsis haum Titanium
Kev txheeb xyuas ntawm Titanium Tus Nqi thiab Carbonitride Density

Rau cov neeg yuav khoom xav tau 347 rau chlorinated seawater kev pabcuam muaj ob txoj hauv kev pov thawj. Thawj yog kev tshuaj xyuas tshuaj rau titanium, los ntawm ICP lossis OES. Txais: Ti<0.01-0.02% for life >8 xyoo. Qhov thib ob yog metallographic (SEM 1,000-}2,000 ×) kev tshawb xyuas ntawm ntu polished los suav cov ntsiab lus carbonitride (ci, angular, 2-10 µm). Txais:<5 particles/mm^2 for 5 year life.

Xaus: Ultra-Titanium Tsawg Specification rau Chlorinated Seawater Pitting Resistance

Nyob rau hauv 347 stainless hlau rhaub sheaths, residual titanium li tsawg li 0.02-0.03% tsim thawj (Nb, Ti) (C, N) carbonitride ntim feem ntawm 0.03-0.05% nyob rau hauv chlorinated seawater (1.5 ppm Cl₂, 20,000℃ppm) ceev nce los ntawm<1 pit/cm² to 2-5 pits/cm² and service life decreases from >8-10 years to 4-6 years. At titanium levels of 0.05-0.08% pit density is >15-30 pits / cm2 thiab perforation tshwm sim tom qab 2-3 xyoos. Engineers sau specs rau 347 sheaths rau marine chlorinated kev pab cuam yuav tsum txwv titanium rau<0.01-0.02% and for the highest pitting resistance upgrade to 316L or duplex 2205. The framework presented here allows buyers to specify 347 chemistry that minimises titanium induced pitting in the most aggressive oxidising marine environments by correlating residual titanium content with primary carbonitride volume fraction, pit initiation density and perforation time in chlorinated seawater.