Vim li cas 316 Stainless Hlau Sheath Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob hauv Bromine- Muaj Cov Dej Txias Dej ntawm 40-60 Degree Undergo Ceev Intergranular Attack ntawm 0.5-1.5 mm / xyoo Thaum Tsis Muaj Cov Tshuaj Chloride Dej ntawm Tib Cov Conductivity Ua Rau Me Me Pitting?

Bromine-raws li biocides, xws li sodium bromide (NaBr) qhib los ntawm oxidants xws li chlorine lossis ozone, tau siv ntau zaus los ua lwm txoj hauv kev tshuaj chlorine hauv kev tswj legionella thiab biofouling hauv cov dej txias, tshwj xeeb tshaj yog qhov tso tawm mus rau ib puag ncig rhiab dej. Kev ua tsis tiav ntawm ntau lub tshuab cua txias thiab ib zaug -los ntawm cov tshuab cua txias qhia tau tias 316 stainless hlau sheathed heaters raug rau cov dej brominated (10-50 ppm tag nrho bromine, 200-1000 ppm bromide ion) raug kev cuam tshuam loj heev ntawm cov phab ntsa ntawm tus nqi ntawm 0.5-1.5 hli feem ntau ntawm 0.5-1.5 hli per. hli. Nyob rau hauv sib piv, tib lub rhaub nyob rau hauv nruab nrab chloride dej ntawm tib conductivity thiab kub (40-60 degree) qhia me me pitting nkaus xwb thiab kav 3-5 xyoo. Qhov sib txawv loj yog vim qhov sib txawv electrochemistry ntawm biocides bromine vs. chlorine. Hauv dej bromine hydrolyses rau hypobromous acid (HOBr) thiab hypobromite ion (OBr). Tsis zoo li hypochlorous acid (HOCl) uas nyiam khaws cov txheej txheem tsis zoo ntawm cov hlau tsis muaj steel, HOBr yog qhov hnyav dua oxidiser uas nkag mus thiab cuam tshuam cov ciam teb, tshwj xeeb tshaj yog tias chromium deficiency tshwm sim los ntawm vuam lossis me me rhiab heev. Ntxiv mus, bromide ions yog loj thiab ntau polarisable tshaj li chloride ions, uas ua rau lawv yooj yim adsorb rau ntawm hlau nto thiab tshem tawm oxides tiv thaiv nyob rau hauv grain ciam teb. Kev sib xyaw ua ke ntawm kev txhoj puab heev oxidising biocide (HOBr) thiab muaj zog adsorbing halide (Br-) ua rau muaj kev sib koom ua ke uas propagates raws li cov ciam teb (intergranular es tsis yog pitting) ua rau poob sai ntawm cov neeg kho tshuab kev ncaj ncees. Txoj kev tshawb no kwv yees cov intergranular corrosion kinetics ntawm 316 nyob rau hauv brominated txias dej thiab muab biocide tswj thiab cov ntaub ntawv xaiv cov txheej txheem.

Electrochemistry ntawm Chlorine thiab Bromine Biocides ntawm 316 Stainless Hlau
Sodium bromide tsis corrosive rau 316 stainless hlau nyob rau hauv nws tus kheej. Cov biocide yog tsim los ntawm kev sib ntxiv ntawm cov oxidant (sodium hypochlorite, ozone los yog hydrogen peroxide) rau bromide uas muaj dej los tsim cov kua qaub hypobromous: 2 NaBr + HOCl → HOBr + NaCl + NaBr Hypobromous acid (HOBr) muaj tus qauv txo qhov peev xwm ntawm +1.33 V qis dua li ntawm SHE }, me ntsis oxidation kinetics ntawm hypobromous acid nyob rau hauv stainless hlau nto yog sai dua vim hais tias ntawm lub loj loj thiab tsis muaj zog hydration plhaub ntawm bromine. HOBr yog ib qho nruab nrab molecule thiab li no tuaj yeem nkag mus rau cov yeeb yaj kiab tsis yooj yim dua li anionic OCl-.

Qhov sib txawv tseem ceeb yog HOBr oxidises grain ciam teb carbides (Cr2 3C 6) aggressively tshaj HOCl, yog li hloov chromium carbides rau soluble chromate hom thiab tawm carbon nplua nuj, chromium depleted voids ntawm lub grain ciam teb. Thaum cov qoob loo ciam teb chromium yog depleted hauv qab li 12%, tus ciam teb ua anodic rau cov nplej sab hauv thiab intergranular corrosion txuas ntxiv txawm tias tsis muaj cov tshuaj chloride ntau ntau.

Potentiodynamic polarization ntawm 316 stainless hlau nyob rau hauv 500 ppm bromide (raws li NaBr) nrog 20 ppm active bromine (raws li HOBr) ntawm 50℃qhia ib tug passive ntau yam ntawm −100 mus rau +300 mV vs SCE, tab sis ib tug loj passive tam sim no ceev ceev (5 µs²) chloride (5 µs² / cm²). Qhov tseem ceeb tshaj, qhov kev sib hloov pauv ntawm + 300 mV yog nrog los ntawm kev nce nrawm ntawm tam sim no, uas yog sib xws ntawm qhov chaw thiab tsis nyob hauv thaj chaw xws li chloride pitting. Qhov kev tawm tsam tsis sib xws no yog tus ntiv tes electrochemical ntawm intergranular corrosion.

Quantification ntawm intergranular corrosion tus nqi hauv bromine muaj dej
Cov kev ntsuas immersion tswj tau ua tiav ntawm 316 stainless hlau qauv (niam txiv hlau tov-annealed, welded kuaj nrog txiav txim siab sensitisation) nyob rau hauv cov khoom cua txias nrog sib txawv bromide thiab nquag bromine concentrations ntawm 50℃. Cov dej kuj tseem muaj 200 ppm chloride (NaCl) raws li keeb kwm yav dhau hauv dej txias. Lub sij hawm raug yog 1000 teev thiab biocide tau ntxiv txhua hnub kom tswj tau cov ntsiab lus bromine.

Tag Nrho Bromide (ppm) Active Br 2 Sib npaug (ppm as HOBr) Chloride (ppm) Kub ( degree) Corrosion Rate (mm / xyoo) Corrosion morphology Intergranular nres qhov tob (µm tom qab 1000 teev)
0 (tswj) 0 200 50 0.03 Tsis muaj 0 100 5 200 50 0.12 me me pitting 5 200 10 200 50 0.35 Mixed pitting + intergranular 25 500 20 200 50 0.70 Intergranular dominant 65 1000 50 200 50 1.20 Severe intergranular 110 500 20 0 (tsis muaj chloride) 50 0.55 Intergranular 50 500 20 200 40 0.40 Mixed 35 500 20 200 60 1.10 Severe (1 oxidant) 200 50 0.04 Tsis muaj 0
The addition of chloride (200 ppm) increased the rate of intergranular attack by about 30% above that with bromide alone. However, bromide with no chloride still generated considerable intergranular corrosion. The crucial factors are temperature and active bromine concentration (not only total bromide). Severe intergranular assault takes place above 15-20 ppm active bromine at 50°C with rates >0.5 hli / xyoo.

Synergy ntawm Bromine Attack thiab Weld Sensitization
Ib qho EPR- ntsuas qib ntawm rhiab heev ntawm 6-8% hauv welded 316 cov qauv (raws li -welded) ua rau muaj kev cuam tshuam loj heev ntawm kev sib txhuam ntawm cov dej brominated piv rau cov niam txiv hlau. Tias yog vim li cas cov qoob loo ciam teb hauv HAZ twb tsis muaj chromium thiab tau nyiam los ntawm HOBr.

Qauv Hom EPR DOS (%) Corrosion Rate nyob rau hauv 500 ppm Br- + 20 ppm HOBr + 200 ppm Cl- , 50℃(mm/yr)Intergranular Attack Depth (µm tom qab 500 h) Failure Mode
Niam txiv hlau (kev daws teeb meem-annealed)<1 0.70 35 Intergranular, uniform 
HAZ (raws li welded, 1.5 hli phab ntsa) 6 1.40 110Heavy intergranular, grain poob,
Weld hlau (autogenous, 11% ferrite) 4 1.10 80 Intergranular + ferrite nres 316L (0.02 % C) niam txiv hlau<1 0.65 30According to the standard 316
Post weld tov annealed (1050 degree)<1 0.72 38No welding particular acceleration
HAZ nyob rau hauv raws li -welded mob deteriorated ntawm yuav luag ob zaug tus nqi ntawm niam txiv hlau (1.40 piv rau 0.70 hli / xyoo) thiab yuav nkag mus rau ib tug 1.5 hli phab ntsa nyob rau hauv txog 1,000 h (6 lub lis piam) piv nrog 2,500 h (3.5 lub hlis) rau cov niam txiv hlau. Txawm tias cov tshuaj annealed niam txiv hlau corrodes sai heev rau lub sij hawm ntev kev pab cuam qhia tau hais tias 316 yog qhov tseem ceeb tsis haum rau tas mus li raug rau active bromine qib siab tshaj 10 ppm ntawm 50℃tsis hais cov weld zoo.

Field Failures los ntawm Cooling Towers & Industrial Water Systems
Kev tshawb fawb ntawm 316 stainless hlau clad cua sov siv nyob rau hauv cov dej txias nrog bromine -raws li biocides nyob rau hauv 11 industrial chaw pom zoo raws li cov qauv tsis ua hauj lwm:

Dej Txias Chemistry FacilityActive Bromine Control (ppm) Kub (degree) Cua sov Hom Kev Pabcuam Lub Neej (hli) Hom Tsis Ua Haujlwm
Txias ntauwd ntawm fais fab nroj tsuag 300 ppm Br⁻, 150 ppm Cl⁻ 15-25 (nruam) 45-55 316L welded flange 3-5 Intergranular cracking ntawm HAZ
Tshuaj tsob nroj recirculating voj 800 ppm Br^-, 100 ppm Cl- 10-15 (intermittent) 50 316 seamless, tsis muaj welds 6-8 Intergranular quab yuam ntawm lub hauv paus hlau
Cov ntaub ntawv chaw txias (kaw lub voj voog) 100 ppm Br-, 50 ppm Cl⁻ 5-8 (kev poob siab txhua lub lim tiam) 40 316L electropolished 14 Mixed pitting / intergranular corrosion
Chiller rau kev ua zaub mov 50 ppm Br⁻ 80 ppm Cl⁻ 3-5 (nruam) 25 316 seamless 36 Mild pitting nkaus xwb (tau txais)
Txias ntauwd roj refinery 500 ppm Br-, 300ppm Cl- 20 (cont.) 55 316L welded 2-3Severe, perforated, intergranular
Refinery cooling tower case: 316 sheaths ua tsis tau txhua txhua 2-3 lub hlis. Cov kev ua tsis tiav tau hais los ntawm kev hloov lub plhaub rau titanium Qib 2 thiab thawj txheej tau ua haujlwm tau 36 lub hlis. Cov dej txias chemistry tsis tau hloov pauv, tsuas yog cov ntaub qhwv tau hloov kho.

Lwm cov khoom siv rau Brominated Cooling Water Service
Kev ntseeg siab rau lub sijhawm ntev yuav tsum tau hloov kho cov khoom siv vim qhov kev ua phem intergranular sai ntawm 316 hauv active bromine concentrations ntau dua 10 ppm ntawm 40-60 deg. C.

500 ppm Br- + 20 ppm HOBr + 200 ppm Cl-, 50°C (mm/year) Corrosion Rate of Sheath MaterialIntergranular Attack? Relative Cost (versus 316) Recommended for Active Br >10 ppm
316 Stainless Hlau 0.70 Yog, hnyav 1.0 Tsis yog (tsis ua tiav 3-6 lub hlis)
317L (Mo siab dua) 0.55 Yog 1.3 Marginal, txwv lub neej 904L (UNS N08904) 0.20 Tsawg (kev xeb dav dav) 2.5 Tau txais 12-24 lub hlis
Alloy 825 (UNS N08825) 0.08 Tsis muaj 4.0 Zoo, 36-60 lub hlis
Alloy C-276 (UNS N10276)<0.02 None 8.0 Very Good
Titanium Qib 2 (UNS R50400) < 0.01None 2.2 Zoo heev, nyiam dua
Titanium Qib 7 (UNS R52400)<0.01None 2.5 Great for higher temperatures
Titanium Qib 2 yog kev txhim kho kev lag luam tshaj plaws rau kev pabcuam dej txias brominated. Nws muaj kev tiv thaiv rau intergranular quab yuam thiab resistant rau ob qho tib si HOBr thiab bromide ions. Cov ntaub ntawv teb los ntawm ntau qhov chaw txias ntauwd qhia tias titanium sheaths kav ntev li 5-10 xyoo, piv rau 3-6 lub hlis rau 316.

Specification Language rau Brominated Cooling Dej rhaub
Cov kws tsim khoom siv hluav taws xob cua sov raj rau cov dej txias txias dosed nrog bromine -raws li biocides - piv txwv li, txhua qhov system uas sodium bromide yog dosed nrog ib qho oxidant - yuav tsum xav tias cov qib bromine nquag ntawm lub rhaub dej yuav siab dua 10 ppm vim muaj kev cuam tshuam hauv zos, txawm tias qhov ntsuas ntau tsawg. Rau txhua daim ntawv thov qhov twg cov bromide concentration ntau dua 100 ppm thiab qhov kub siab tshaj 40 degree, cov ntaub ntawv sheath yuav tsum tau teev raws li qhov tsawg kawg nkaus Titanium Qib 2 (UNS R50400) los yog Qib 7 (UNS R52400). Yog tias 316 stainless hlau yuav tsum tau siv rau hauv cov txheej txheem uas twb muaj lawm, cov kev txwv kev ua haujlwm hauv qab no yuav tsum suav nrog: tswj cov bromine concentration ntawm tsawg dua 5 ppm txhua lub sijhawm siv qhov tseeb ORP tswj (lub hom phiaj 600-650 mV, tsis siab dua); zam kev poob siab ntawm oxidants nyob ze ntawm lub rhaub; thiab sheaths yuav tsum tau soj ntsuam txhua hli rau intergranular nres siv ultrasonic thickness ntsuas los yog dye penetrant kuaj ntawm welded cheeb tsam. Nkag siab tias cov dej brominated yog inherently txhoj puab heev rau 316 dua li chlorinated dej nyob rau tib theem biocide. Nkag siab tias kev tawm tsam intergranular, tsis yog pitting, yog qhov tsis ua haujlwm loj. Cov kws tsim khoom tuaj yeem ua tiav cov kev pabcuam cua sov zoo nyob rau hauv lub xyoo, tsis yog lub hlis, hauv brominated txias tshuab los ntawm kev kho dua tshiab rau titanium lossis npib tsib xee alloys.