Vim li cas Titanium Immersion Rhaub Nrog Ib Lub Vev Xaus Xaus Tsis Txaus Siab Los Ntawm Crevice Corrosion Ntawm Weld Root Tshaj Los Ntawm Kev Nyuaj Siab Hauv Ib 5% Sodium Hypochlorite Tshuaj Ntawm 60 degree?
Tso lus
Hauv 5% sodium hypochlorite (NaOCl) ntawm 60 degree, titanium nthuav tawm qhov tsis tshua muaj corrosion ntawm 0.01-0.05 hli hauv ib xyoos vim qhov muaj zog oxidizing ib puag ncig. Txawm li cas los xij, lub welded kawg cap ntawm lub rhaub dej kub muaj qhov sib txawv ntawm cov hauv paus weld- qhov sib txawv ntawm lub hau kawg thiab lub raj phab ntsa nyob rau sab hauv ntawm lub rhaub. Qhov no crevice geometry ntxiab stagnant electrolyte. Hypochlorite decomposes nyob rau hauv lub crevice los tsim chloride thiab oxygen, thiab chlorides mloog zoo rau 5-10 npaug ntawm tej concentration. Cov zaj duab xis passive lov nyob rau hauv lub crevice, thiab tus nqi corrosion accelerates mus rau 0.3-1.0 hli ib xyoo, uas yog 10-100 lub sij hawm sai tshaj li niaj hnub thinning. Qhov tsis ua hauj lwm tshwm sim zoo dua ntawm cov hauv paus hniav, feem ntau tsis pom sab nraud corrosion.
Lub Mechanism ntawm Crevice Corrosion ntawm Weld Root hauv Hypochlorite
Nyob rau hauv cov tshuaj hypochlorite ntau, oxidizing ib puag ncig tswj cov yeeb yaj kiab ruaj khov. Nyob rau hauv lub weld cag crevice, qhov txwv geometry txwv tsis pub oxygen ntxiv. Hypochlorite decomposes: 2OCl⁻ → O₂ + 2Cl⁻. Cov chloride concentration tsim, thiab oxygen depleted. Lub zos pH poob raws li hypochlorous acid cov ntaub ntawv. Kev sib xyaw ua ke ntawm cov tshuaj chloride siab, cov pa oxygen tsawg, thiab acidic pH rhuav tshem cov zaj duab xis passive. Lub loj loj sab nraud cathode (tus so ntawm lub rhaub) tsav ceev anodic dissolution nyob rau hauv lub crevice. Lub weld hauv paus geometry kuj muaj qhov seem tensile kev nyuaj siab los ntawm vuam, uas ua rau kom tawg pib.
Quantitative Crevice Corrosion Rate ntawm Weld Root
Controlled testing in 5% NaOCl at 60°C over 1,000 hours has established the following corrosion rates for Grade 2 titanium at different heater locations. For the tube body (smooth surface, no crevice), the uniform corrosion rate is 0.01–0.03 mm per year, and the surface remains bright with no pitting. For the external weld toe (the outside of the welded end cap), the corrosion rate is 0.02–0.05 mm per year, and the surface shows light etching. For the weld root crevice (inside gap of 0.1–0.3 mm), the crevice corrosion rate is 0.3–0.8 mm per year, and severe grooving occurs, with perforation of a 1.2 mm wall within 1,500–4,000 hours. For the weld root with a poorly fitted end cap (gap >0.5 hli), qhov crevice corrosion nce mus rau 0.5-1.2 hli ib xyoo, nrog perforation nyob rau hauv 1,000-2,500 teev.
Kev cuam tshuam ntawm Hypochlorite Concentration thiab Kub ntawm Crevice Severity
Qhov hnyav ntawm weld cag crevice corrosion nce nrog hypochlorite concentration thiab kub. Nyob rau ntawm 1% NaOCl thiab 60 degree, qhov crevice corrosion yog 0.15-0.40 hli ib xyoo. Ntawm 5% thiab 60 degree, tus nqi yog 0.30-0.80 hli ib xyoo. Ntawm 10% thiab 60 degree, tus nqi nce mus txog 0.50-1.20 hli hauv ib xyoos. Ntawm 5% thiab 40 degree, tus nqi yog 0.10-0.25 hli ib xyoo. Ntawm 5% thiab 80 degree, tus nqi nce mus rau 0.50-1.00 hli hauv ib xyoos. Lub xub ntiag ntawm chlorides nyob rau hauv cov tshuaj hypochlorite (los ntawm cov laus bleach) ua rau cov crevice corrosion ntau dua 30-50%.
Weld Root Design and Mitigation Guide for Hypochlorite Service
Cov lus hauv qab no muab cov lus pom zoo rau qhov kawg cap weld tsim thiab lwm yam kev teeb tsa los tiv thaiv crevice corrosion hauv 5% sodium hypochlorite ntawm 60 degree.
| Weld Tsim | Txoj kab uas hla (mm) | Xav Tau Crevice Corrosion Rate (mm/xyoo) | Lub sij hawm rau Perforation ntawm 1.2 hli phab ntsa (teev) | Kev pom zoo |
|---|---|---|---|---|
| Tag nrho nkag mus weld, av flush | 0 (tsis muaj kev sib tw) | <0.05 | >10,000 | Kev xyaum zoo tshaj plaws |
| Ib nrab nkag mus rau weld, qhov sib txawv<0.1 mm | <0.1 | 0.15–0.35 | 3,500–8,000 | Txais nrog kev tshuaj xyuas |
| Ib feem nkag mus vuam, qhov sib txawv 0.1-0.3 hli | 0.1–0.3 | 0.30–0.80 | 1,500–4,000 | Marginal |
| Lap weld (cap hla lub raj), qhov sib txawv 0.3-0.5 hli | 0.3–0.5 | 0.50–1.00 | 1,200–2,500 | Tsis pom zoo |
| Butt weld nrog backing nplhaib | 0.2–0.4 | 0.40–0.90 | 1,300–3,000 | Zam |
Engineering Beyond Weld Design
Qib titanium cuam tshuam rau crevice corrosion kuj. Qib 7 (palladium{2}}stabilized) muaj 3-5 lub sij hawm pib lub sij hawm ntev dua thiab 50-70% qis dua tus nqi nthuav tawm dua qib 2 hauv hypochlorite crevices. Qib 12 muaj kev txhim kho nruab nrab. Phab ntsa thickness muab cov khoom pub dawb; ib lub 2.0 hli phab ntsa nrog crevice corrosion ntawm 0.5 hli ib xyoo ciaj sia 4 xyoo. Lub hau kawg yuav tsum tau tsim los ua ib qho kev nkag mus rau pob tw, hauv av yaug rau sab hauv thiab sab nraud. Yog tias tsis tuaj yeem zam tsis tau, sau qhov sib txawv nrog PTFE daim kab xev lossis fluoropolymer sealant tiv thaiv electrolyte ingress. Kev tso dej tawm ib ntus ntawm lub rhaub dej nrog cov dej tshiab txo qis hypochlorite concentration hauv cov crevices.
Ua ib qho kev qhia tshwj xeeb
Rau lub titanium immersion rhaub nyob rau hauv 5% sodium hypochlorite ntawm 60 degree, qhia tag nrho nkag mus rau lub taub qab vuam rau lub hau kawg, av yaug rau sab hauv thiab sab nraud los tsim ib tug crevice - dawb geometry. Yog tias tsis tuaj yeem nkag mus rau qhov vuam tag nrho, qhia qhov tsawg kawg nkaus qhov sib txawv ntawm qhov sib txawv ntawm qhov tsawg tshaj li 0.1 hli thiab yuav tsum tau tshaj tawm -weld tshuaj xyuas kom paub tseeb qhov sib txawv. Rau cov ntawv thov tseem ceeb, qhia qib 7 titanium thiab ntxiv cov helium leak test los xyuas qhov kev ncaj ncees. Thaum lub sijhawm ua haujlwm, tshuaj xyuas thaj tsam ntawm peb lub hlis twg siv lub borescope lossis dye penetrant; Yog tias cov khoom siv corrosion pom hauv qhov vuam, hloov lub rhaub. Los ntawm kev tsim cov crevice{10}}dawb weld cag, tus kws ua haujlwm tshem tawm cov txheej txheem corrosion ceev, cia lub rhaub kom ua tiav lub neej kev pab cuam tsuas yog los ntawm kev ua kom nyias nyias.
