Raws li kev sib xyaw tshwj xeeb ntawm cov tshuaj chlorine seem thiab pH puas 316 Stainless Steel Heater Sheath Hloov los ntawm Passive rau Pitting hauv Cov Dej Kub Hauv Tsev ntawm 60 degree

Kev cuam tshuam ntawm Passivity nyob rau hauv Potable Water Systems Induced los ntawm Disinfection

Hauv cov tshuab dej kub hauv tsev siv 316 stainless hlau sheathed hluav taws xob cua sov raj (point- ntawm - siv cov cua sov, cov dej kub, cov voj voog rov qab, thiab lwm yam) kev siv cov tshuaj chlorine seem (ntxiv rau cov roj chlorine, sodium hypochlorite lossis chloramine rau tshuaj tua kab mob) sawv cev rau kev pheej hmoo ntawm pitting corrosion tsis pom nyob rau hauv untreated. Kev ruaj ntseg lossis kev tawg hauv zos ntawm cov yeeb yaj kiab tsis zoo ntawm 316 nyob ntawm cov tshuaj chlorine dawb (Cl2, HOCl, OCl-) thiab pH ntawm 60℃(qhov nruab nrab ntawm cov dej kub hauv tsev) . 316 nyob qis qis qis dua qhov pib dawb chlorine concentration ntawm ~ 2 ppm ntawm pH 7.5. Saum toj no 3-4 ppm ntawm tib pH pitting pib hauv lub lis piam mus rau hli. Kev cuam tshuam ntawm pH yog qhov tseem ceeb: ntawm pH 8.5 qhov nkag siab ntawm cov tshuaj chlorine ob npaug thiab ntawm pH 6.5 nws yog halved. Kab lus no kwv yees cov tshuaj chlorine-pH qhov pib rau pitting pib ntawm 316 sheaths hauv 60℃potable dej thiab muab cov qauv kev kho dej rau lub rhaub kom ntev.

Lub Mechanism ntawm Chlorine Induced Pitting

Cov tshuaj chlorine dawb nyob hauv dej yog qhov sib npaug ntawm hypochlorous acid (HOCl) thiab hypochlorite ion (OCl{0}}), qhov sib piv yog nyob ntawm pH. HOCl predominates ntawm pH <7.5; OCl- predominates ntawm pH > 7.5. HOCl yog qhov muaj zog oxidant dua li OCl- thiab muaj kev sib ntaus sib tua ntau dua rau cov yeeb yaj kiab stainless hlau. Cov tshuaj chlorine ntawm cov hlau saum npoo tuaj yeem ua rau hauv zos tawg cov chromium oxide zaj duab xis tsim los ntawm kev tsim cov chromium chloro soluble - complexes los yog los ntawm kev tsim cov oxidising heev uas ua rau transpassive dissolution (oxidation ntawm Cr 3+ rau soluble Cr 6+). Qhov muaj zog oxidising muaj peev xwm ntawm cov tshuaj chlorine tswj cov tshuaj muaj zog hauv zos uas ua rau muaj qhov chaw ruaj khov tom qab cov yeeb yaj kiab passive tau tawg ntawm qhov chaw tsis muaj zog, feem ntau ntawm MnS suav nrog lossis khawb qhov chaw. Chlorine induced pitting yog txawv ntawm chloride induced pitting qhov twg ntau pua mus rau txhiab ppm Cl- yuav tsum tau, chlorine yog ib qho muaj zog oxidant thiab pitting tuaj yeem loj hlob ntawm cov tshuaj dawb dawb ntawm 1-5 ppm.

Quantified Thresholds rau Pitting nyob rau hauv 60℃Domestic Kub Dej

Ua raws li kev sim ntsuas ntawm 316 stainless hlau (Ra=0.4 µm polished tiav) hauv cov dej kub hluavtaws hluavtaws (100 ppm Cl-, 80 ppm SO4-2, 120 ppm CaCO3 hardness) ntawm 60℃siv cov tshuaj dawb chlorine pH Cl2 asidion pib (2me) Cov ciam teb tau raug txheeb xyuas tom qab 1,000 teev ntawm qhov raug.

Free Residual Chlorine (ppm as Cl2) pH Dominant Chlorine Species Pitting Initiation Sijhawm (teev) Qhov tob tob tshaj plaws tom qab 1,000 teev (µm) Lub Sijhawm rau Perforation (1.5 hli phab ntsa) Pom zoo rau Kev Pabcuam Dej Kub Hauv Tsev<0.5 6.5-8.5 Mixed No pitting <5 >30 xyoo Yes
0.5-1.0 7.0-8.5 Mixed >5,000 (yuav tsis pib)<10 >20 xyoo Yes
7.5-8.5 1.0-1.5 OCl⁻ dominant 2,000-5,000 10-30 10-20 yrsAcceptable with supervision 1.0-1.5 6.5-7.5 HOCl dominant 1,000-2,000 30-60 5-10 xyoo Marginal
1.5-2.0 7.5-8.5 Fl⁻ tseem ceeb 1,000-2,000 40-80 4-8 xyoo Marginal
1.5-2.0 6.5-7.5 HOCl dominant 500-1, 000 80-150 2-5 xyoo Tsis Qhia
2.0-3.0 7.5-8.5 OCl⁻ tseem ceeb 300-800 100-200 2-4 xyoo Tsis qhia
2.0-3.0 6.5-7.5 HOCl tseem ceeb 100-300 200-400 1-2 xyoo Tsis tau
3.0-5.0 7.5-8.5 OCl- dominating 100-300 200-500 1-2 xyoo Tsis tau
3.0-5.0 6.5-7.5 HOCl tseem ceeb 50-100 400-800 6-12 lub hlis Tsis lees txais5.0 Ib qho HOCl lossis OCl⁻<50 >500 <6 months Unacceptable
Kev cuam tshuam ntawm qhov kub thiab txias ntawm chlorine Aggressiveness

Qhov chaw nyob hauv lub rooj yog rau 60 degree. Raws li qhov kub thiab txias, cov tshuaj chlorine ua nruj dua vim tias muaj qhov sib txawv ntau dua thiab cov yeeb yaj kiab tsis tshua muaj zog. Hauv qab 60℃qhov tso cai chlorine cov ntsiab lus nce yuav luag linearly nrog txo qhov kub.

Dej Kub (degree) Max Dawb Chlorine rau 5 Xyoo Pitting Dawb Lub Neej ntawm pH 7.5 (ppm) Pom Zoo Ua Haujlwm
40 3.0 Tsis muaj qhov tshwj xeeb yuav tsum tau ua
50 2.2 Monitor if >2.0 ppm 60 1.5 Dechlorinate if >1.5 ppm 70 1.0 Dechlorination pom zoo 80 0.7 Dechlorination yuav tsum tau 90 0.5 316 tsis pom zoo; upgrade rau titanium
Cov tswv yim pom zoo rau kev kho cov dej hauv cov dej kub hauv tsev

316 encased heaters nyob rau hauv tsev cov dej kub hauv tsev ntawm 60℃muaj cov qauv kev kho dej hauv qab no rau lub sijhawm ntev pitting dawb.

Dawb Chlorine Residual (ppm) pH pom zoo ua<0.5 Any No action required
>7.5 Tsis ua haujlwm; 0.5-1.0
0.5-1.0 <7.5 Adjust pH to >7.5 nrog sodium hydroxide los yog ua tib zoo saib xyuas
1.0-1.5 >8.0 Txais; tshuaj xyuas txhua 2 xyoos
1.0-1.5 7.0-8.0 Txo cov tshuaj chlorine lossis hloov mus rau 316L nrog electropolished tiav
1.5-2.0 >8.0 Txo cov tshuaj chlorine lossis hloov lub rhaub
1.5-2.0 <8.0 Dechlorination (injection of activated carbon or sodium sulphite) necessary2.0 Any Dechlorination necessary; upgrade to titanium?
Field Identification of Chlorine-Caused Pitting

Cov tshuaj chlorine residual pitting ua rau cov pits uas feem ntau me me (0.1-} 0.5 mm txoj kab uas hla), ntau, thiab sib npaug faib thoob plaws hauv lub plhaub (raws li qhov tsis zoo rau chloride-induced pitting uas loj dua thiab tsawg dua). Cov pits feem ntau nyob ib puag ncig los ntawm lub nplhaib cathodic ci ntsa iab, thiab muaj xim av tsaus lossis dub chaw (manganese oxide los ntawm kev sib xyaw ua ke). Thaum ob qho tib si cov tshuaj chlorine siab thiab cov tshuaj chloride siab (tshaj 200 ppm) muaj nyob hauv dej, ob qho kev cuam tshuam ua haujlwm sib koom ua ke thiab qhov pib qis dua 30-50%. Yog tias lub rhaub dej kub hauv tsev ua tsis tiav los ntawm pitting li ntawm 2-3 xyoos, cov tshuaj chlorine seem yuav tsum tau sim ntawm ntau qhov chaw (inlet, tank, tso zis) kom pom tias spikes tshaj qhov pib.

Xaus 316 Lub Hwj Chim Lub Neej @ 60 Degree Tswj Cov Tshuaj Chlorine Residual

Ntawm pH 7.5, residual dawb chlorine concentrations siab tshaj 1.5 ppm accelerate pitting corrosion ntawm 316 stainless hlau encased rhaub nyob rau hauv tsev cov dej kub ntawm 60℃nyob rau hauv 2-5 xyoo, txo lub cua sov lub neej los ntawm ib yam ntawm 3-10 piv rau dechlorinated dej. Cov pH siab dua (8.0-8.5) tuaj yeem muaj ob npaug ntawm chlorine concentration. Tsawg pH (6.5-7.0) txiav qhov tso cai txwv ib nrab. Cov kws tsim qauv qhia txog 316 sheaths rau cov dej kub uas muaj peev xwm yuav tsum tau sau cov ntaub ntawv zoo nrog rau cov tshuaj chlorine seem thiab pH ntawm qhov ntsuas kub ntawm kev ua haujlwm. Rau cov tshuab uas muaj cov tshuaj chlorine ntau dua 1.5 ppm, dechlorination (activated carbon filtration los yog sodium sulphite txhaj) los yog upgraded rau 316L nrog electropolished tiav yog qhia. Ntawm no peb muab cov txheej txheem uas tso cai rau cov neeg yuav khoom xaiv cov kev kho dej uas tiv thaiv 316 sheaths los ntawm cov tshuaj tua kab mob-induced corrosion hauv kev pabcuam dej kub hauv tsev los ntawm kev sib txuas cov tshuaj chlorine concentration thiab pH rau quantifiable pitting start durations.