Yuav Ua Li Cas Lub Nruam Nrab Nb (C, N) Carbonitride Particles nyob rau hauv 347 Heater Sheath Tubing Tswj Pitting Initiation Site Density nyob rau hauv siab -Chlorine (2 ppm Cl₂) Seawater ntawm 40 degree
Tso lus
Lub complex suav nrog raws li qhov loj Nucleation Site ntawm Vat Pit hauv Oxidising Conditions
Complex niobium carbonitride (Nb(C,N)) hais yog qhov chaw tseem ceeb rau pitting pib nyob rau hauv 347 stainless hlau (Nb-stabilized) sheathed hluav taws xob cua sov raj nyob rau hauv chlorinated seawater (2 ppm residual chlorine, 20,000 ppm 4 ntawm ntug dej hiav txwv, Cl- cov nroj tsuag txias), desalination preheaters, los yog marine heat exchangers. Tsis zoo li MnS suav nrog (uas yaj hauv qhov xwm txheej chlorinated) lossis Al2O3 (uas yog inert), Nb (C, N) hais yog ib nrab- coj thiab tuaj yeem ua cathodic rau 347 matrix zoo li TiN hauv 316L. Lub qhov pib qhov ceev yog ncaj qha proportional rau qhov ntim feem ntawm Nb (C, N) (txiav txim siab los ntawm niobium, carbon thiab nitrogen cov ntsiab lus). Rau Nb (C, N) ntim feem<0.02-0.05% (Nb:C+N ratio <8:1, excellent stabilisation) pit densities are low (<0.5 pits/cm2) and service life is >10 years. At Nb(C,N) >0.10-0.15% (excess niobium or excessive nitrogen) pit densities are >10-20 pits / cm2 thiab perforation hauv 2-3 xyoos. Hauv tsab xov xwm no, qhov sib txuas ntawm Nb (C, N) ntim feem, qhov pib qhov ceev thiab kev pab cuam lub neej nyob rau hauv chlorinated seawater ntawm 40℃yog kom muaj nuj nqis.
Mechanism ntawm Nb(C,N)-Txhim kho Pitting hauv Chlorinated Seawater
Niobium carbonitride (Nb (C, N)) yog lub ntsej muag nruab nrab cubic (FCC) cov khoom uas muaj hluav taws xob zoo heev thiab cathodic rau austenitic matrix. Hauv cov dej ntsev chlorinated (muaj peev xwm oxidation siab vim Cl2), cov tshuaj tiv thaiv cathodic (cov pa txo qis thiab cov tshuaj chlorine txo) tshwm sim zoo ntawm Nb (C, N) qhov chaw, tsim cov galvanic ob peb uas ua rau anodic dissolution ntawm 347 matrix nyob ze. Raws li kev tawm tsam MnS uas yaj, Nb (C, N) ruaj khov thiab txuas ntxiv tsav galvanic tam sim no. Lub qhov pib qhov ntom ntom yog ncaj qha ntsig txog tus naj npawb ntawm Nb (C, N) hais rau ntawm qhov chaw.
Quantitative Correlation ntawm Nb(C, N) Volume Fraction thiab Pitting Density
Kev ntsuas immersion ntawm 347 tubing (0.08% C, 0.06% N) nrog cov ntsiab lus niobium sib txawv (kom hloov Nb(C, N) ntim feem) hauv chlorinated hluavtaws seawater (2 ppm Cl 2, 20,000 ppm Cl-) ntawm 5 ,000 teev tom qab pib ceev.
Niobium Cov ntsiab lus (wt%) Carbon (wt%) Nitrogen (wt%) Nb(C,N) Volume Fraction (%) Nb(C,N) Particle Loj (µm) Qhov ntom ntom tom qab 5,000h (pits / cm2) Qhov siab tshaj plaws qhov tob (µm) Lub Sijhawm rau Perforation (1.5 hli dej hiav txwv Chlor, xyoo)<0.05 (No Nb) 0.08 0.06 <0.01 <1 <0.1 <10 >15 Yog lawm (tab sis tsis ruaj khov)
0.20 0.06 0.05 0.02-0.04 1-2 0.2-0.5 10-20 10-15 Yes 0.30 0.06 0.06 0.04-0.06 1-3 0.5-1 15-30 8-12 Acceptable 0.40 0.06 0.06 0.06-0.08 2-4 1-2 25-40 5-8 Marginal 0.50 0.06 0.06 0.08-0.12 2-5 2-5 40-60 3-5 Not recommended 0.60 0.06 0.06 0.12-0.15 3-6 5-10 50-80 2-3 No 0.80 0.06 0.06 0.15-0.20 4-8 10-20 70-100 1.5-2 No >1.00 >0.06 >0.06 >0.20 >5 >20 >100 <1.5 No
Morphology ntawm Nb (C, N) raws li kev cuam tshuam los ntawm Kev Kho Mob Kub Kub Stabilization
Lub stabilization anneal (850-900 degree) ua rau nag lossis daus ntawm finer, nquag Nb (C, N) hais, uas yuav txhim khu lub qhov ntom yog tias niobium ntau dhau.
Kev kho cua sov Nb(C,N) Particle Size (nm) Nb(C,N) Volume Fraction (%) Qhov ntom ntom (pits/cm2, 0.50% Nb) Pom zoo rau Chlorinated Hiav Txwv Dej
Cov tshuaj anneal nkaus xwb (1,050℃, WQ) 500-2,000 nm 0.08-0.12 2-5 Txais Stabilization 850 degree, 2h 50-200 nm 0.10-0.15 5-10Tsis qhia (ntau qhov pits, finer particles)
Stabilization 900 degree, 4h 100-300 nm 0.10-0.15 3-8 Tsis pom zoo (ntau qhov pits)
Raws li -kos, tsis muaj stabilization 500-3,000 nm 0.06-0.10 1-3 Txais
Cov tswv yim pom zoo rau 347 hauv dej hiav txwv, chlorinated
Rau 347 sheathed heaters nyob rau hauv chlorinated ntsev ntawm 40 degree, cov nram qab no niobium thiab stabilization tsis txo Nb (C, N) induced pitting:
Kev Pabcuam Lub Neej (xyoo) Qhov siab tshaj plaws Nb(C,N) Volume Fraction (%) Max. Niobium (wt%) Yam tsawg kawg nkaus Carbon thiab Nitrogen (% wt) Stabilization pom zoo10<0.04 0.30 0.10 None (solution anneal only)
5-10 <0.06 0.40 0.12 None 3-5 <0.08 0.45 0.12 None (avoid stabilisers)
2-3 Not acceptable >0.50 Ib qho Kev Txhim Kho rau duplex lossis 316L
Xaus: Tswj ntawm Nb (C, N) rau pitting kuj
We have identified the initiation sites for pitting of 347 stainless steel heater sheaths exposed to chlorinated seawater (2 ppm Cl2, 20,000 ppm Cl-) at 40°C as particles of niobium carbonitride (Nb(C,N)). Volume fractions exceeding 0.06-0.08% (Nb >0.40-0.45%) result in pit densities >2-5 pits/cm 2 thiab txo lub neej kev pab rau 3-5 xyoos. Cov kws kho tsheb uas tau teev tseg 347 sheaths rau marine chlorinated kev pab cuam yuav tsum txwv niobium rau 0.30-0.40% thiab tiv thaiv kom tsis txhob muaj kev ruaj ntseg annealing (uas precipitates nplua Nb(C, N)). Qhov siab tshaj pitting tsis kam nyob rau hauv cov dej hiav txwv chlorinated yog 316L los yog duplex 2205 es tsis yog 347. Cov txheej txheem tau thov ntawm no txuas Nb (C, N) ntim feem pua rau qhov ntom ntom thiab lub sijhawm perforation. Cov neeg yuav khoom tuaj yeem hais qhia 347 chemistry uas txo qis kev cuam tshuam nrog cov pitting hauv oxidising marine ib puag ncig.
