Vim li cas 316 Stainless Hlau Sheath Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Corrosion Hauv qab PTFE Cov Khoom Txhawb Nqa Hauv Nruab Nrab -Chloride Kub Cia Tank?

Cov khoom siv hluav taws xob rau cov hluav taws xob cua sov hauv cov dej kub cia tank feem ntau yog ua los ntawm polytetrafluoroethylene (PTFE) lossis lwm yam fluoropolymers, thiab lawv tau siv los khaws 316 stainless hlau sheath tawm ntawm cov pa roj carbon steel phab ntsa. Qhov kev tsim no tiv thaiv galvanic corrosion ntawm cov hlau tsis sib xws, tab sis qhov tsis ua hauj lwm kev soj ntsuam ntawm kev lag luam dej rhaub thiab thermal cia tshuab qhia tau hais tias lub crevice tsim ntawm PTFE bracket thiab 316 stainless hlau sheath tsim ib qho kev txhoj puab heev hauv zos chemistry txhawb pitting thiab crevice corrosion, feem ntau ua rau lub rhaub dej tsis ua hauj lwm nyob rau hauv 6{{10} 7 pp} tsuas yog 18 lub hlis hauv dej. tshuaj chloride. PTFE cov khoom nws tus kheej yog tshuaj inert tab sis tsis-absorbent non-permeable yam ntxwv ntawm PTFE inhibits oxygen thiab bulk dej los ntawm kev nkag mus rau nruj fissure, uas yog dab tsi ua rau txawv aeration cell tsim. Thaum ib qho tawg tau tsim, cov dej ntim hauv qhov crevice ua cov tshuaj tiv thaiv hydrolysis uas ua rau cov pH hauv zos rau qhov qis qis li 3.5-4.0. Cov chloride ions txav mus rau hauv qhov tob kom khaws cov nqi nruab nrab, ncav cuag qhov siab txog li 10 npaug ntawm cov dej ntau. Kab lus no kwv yees cov kinetics ntawm crevice corrosion nyob rau hauv PTFE txhawb nqa ntawm 316 stainless hlau sheaths thiab tawm tswv yim engineering cov tswv yim kom tsis txhob no tsis ua hauj lwm hom nyob rau hauv dej kub kev pab cuam.

Electrochemical mechanism ntawm crevice corrosion hauv qab uas tsis yog - ntxeem tau polymer txhawb
Lub crevice corrosion mechanism ntawm 316 stainless hlau yuav tsum muaj qhov sib txawv geometric feem ntau me dua 0.1 hli los tsim ib qho chaw tsis muaj zog. Thaum clamped tiv thaiv lub hnab uas muaj roj hmab los yog silicone cushion txheej, PTFE txhawb nqa brackets tuaj yeem tsim qhov khoob ntawm 0.05-0.3 hli, nyob ntawm qhov sib txawv ntawm compression thiab thermal expansion. Thaum cov dej ntau nkag mus rau hauv qhov crevice no, cov pa oxygen hauv lub ntim ntim tau sai sai los ntawm cov txheej txheem cathodic txo ntawm cov hlau. Hauv cov txheej txheem cathodic, oxygen thiab electrons raug txo kom tsim hydroxide ions: O 2 + 2H 2 O + 4e- → 4OH - Txawm li cas los xij, raws li PTFE yog impervious rau diffusion ntawm oxygen, tsis muaj replenishment los ntawm cov dej ntau. Lub ntim me me uas dhau los ua ntxiab yog deaerated thiab hauv zos muaj peev xwm txav mus rau hauv cheeb tsam corrosion active rau 316 stainless hlau. Cov hlau chloride nyob rau hauv qhov crevice undergoes hydrolysis kom muab cov kua qaub dawb: FeCl 2 + 2H 2 O → Fe (OH) 2 + 2HCl Cov txheej txheem autocatalytic no txo ​​cov pH mus rau qib uas depassivate 316 stainless hlau, uas yuav tsum tau tsuas yog 50-100 ppm .com bulk chloride kom tswj tau

Kev sim kev tshawb fawb nrog microelectrodes muab tso rau hauv cov kab nrib pleb ntawm PTFE blocks thiab 316 stainless hlau daim hlau hauv 100 ppm chloride dej ntawm 70℃qhia kev nce qib raws li hauv qab no:

Thawj 24 teev: Bulk pH 7.2, crevice pH 6.5, crevice chloride 120 ppm.

72h ua. Crevice pH 5.2, chloride 280 ppm. Qhib Circuit Court muaj peev xwm hloov ntawm +50 mV rau -250 mV vs Ag/AgCl.

168 teev pH 3.8 chloride 960 ppm (crevice). Qhov pom pitting pib ntawm ntug crevice.

336 teev: pH 3.2, chloride concentration nyob rau hauv crevice 1100 ppm Qhov nkag mus ntau tshaj 0.1 hli ib lub lis piam ntawm 70 degree.

Rau cov dej kub cia tso tsheb hlau luam ntawm 60-80 degree, tus nqi corrosion yog nce los ntawm qhov zoo ntawm 2-3 rau txhua txhua 10℃nce vim qhov nrawm nrawm dua thiab ntau dua aggressive hydrolysis kinetics.

Qhov tseem ceeb dav ntawm qhov sib txawv thiab cov khoom sib haum xeeb teeb meem
Tsis yog txhua qhov tawg yog sib npaug sib npaug. Qhov kev txhoj puab heev tshaj plaws tshwm sim nyob rau hauv ib qho geometric ntau yam thiab PTFE-stainless steel interface ntog rau hauv qhov tseem ceeb. Cov txiaj ntsig ntawm kev tswj kev sib txawv hauv 316 stainless hlau hauv 150 ppm chloride dej ntawm 75℃yog raws li hauv qab no. Kev sib txuas ntawm qhov sib txawv ntawm qhov dav thiab qhov siab tshaj plaws tom qab 500 h yog:

Crevice gap width (mm) Oxygen diffusion stateMaximum Pit Depth (mm) Pit Morphology < 0.02 (raws li cov hlau rau hlau sib cuag) Tsis muaj dej nkag, tsis muaj crevice corrosion 0.00 Tsis nres 0.02 - 0.08 Cov pa oxygen deprivation, txwv dej ingress tob 0.25 - 0.4
0.08 - 0.25 Kev hloov pauv dej nruab nrab, nquag autocatalytic voj voog 0.40-0.70Large undercut qhov
0.25 - 0.50 Tsawg qhov hnyav, ib nrab dej ncig 0.15 - 0.30A tus naj npawb ntawm cov trenches ntiav 0.50 Cov dej tsis pub dawb, cov pa oxygen diffusion ua tau <0.05 Tsawg kawg nres Compression ntawm PTFE kev txhawb nqa brackets los ntawm cov hlua hlau los yog lub caij nplooj ntoos hlav clips feem ntau ua rau qhov sib txawv ntawm 0.05 mm. Qhov no yog vim li cas PTFE yog ib qho teeb meem tshwj xeeb tiv thaiv cov khoom ntxeem tau xws li roj hmab lossis fiber ntau cov khoom sib xyaw. Roj hmab gaskets thiab EPDM (ethylene propylene diene monomer) cov ntaub ntawv yog me ntsis permeable rau oxygen, tso cai rau ib tug gradual passage uas tej lub sij hawm muaj peev xwm txhawb nqa passive tej yam kev mob. PTFE muaj cov pa permeability ntawm ib ncig ntawm 0.5 × 10⁻¹³ cm³·cm / (cm²·s·Pa) thiab yog li xyaum ua ib qho zoo meej oxygen barrier, uas txhais tau hais tias lub crevice ntim yog deaerated kiag li.

Cov ntaub ntawv pov thawj ntawm Kev Pabcuam Kev Txom Nyem ntawm Kev Ua Lag Luam Dej Kub
Hauv paus ua rau kev faib tawm ntawm 247 ua tsis tiav 316 stainless hlau hluav taws xob cua sov raj xa rov qab los ntawm kev lag luam kub dej tso tso tsheb hlau luam (150-500 liter muaj peev xwm, 60-80℃setpoint, hauv nroog dej nrog 40-200 ppm chloride) qhia: 43% ntawm qhov ua tsis tiav pib ntawm PTFE txhawb nqa bracket 3 affed{1% crevices, zones, 18% ntawm lub davhlau ya nyob twg pin ntsaws ruaj ruaj, thiab 8% los ntawm cov pitting dav dav ntawm cov hlua ncaj nraim. Lub sij hawm nruab nrab ntawm kev ua tsis tiav rau PTFE crevice- cuam tshuam txog kev ua tsis tiav yog 14 lub hlis vs 31 lub hlis rau qhov vuam- cuam tshuam txog kev ua tsis tiav thiab 46 lub hlis rau kev ua tsis tiav.

Lub sijhawm tsis ua haujlwm luv dua tau pom rau cov cua sov uas siv PTFE brackets hauv cov dej sov tshaj plaws nyob ze ntawm lub tank hauv qab. Cov dej kub tshaj plaws stratifies nyob rau hauv qis thib peb ntawm lub tso tsheb hlau luam, ncav cuag qhov kub ntawm 5-15℃saum toj no qhov teeb meem, vim muaj cov cua kub hauv zos. PTFE brackets nyob rau hauv cov cua sov ua haujlwm ntawm 75℃bulk kub thiab nyob rau hauv 80-85℃cheeb tsam ua tsis tau tejyam nyob rau hauv nruab nrab ntawm 8-11 lub hlis.

Kev soj ntsuam ntau ntawm cov dej chemistry cov ntaub ntawv los ntawm kev teeb tsa lub rhaub dej ua tsis tiav qhia tau hais tias muaj kev sib txuas siab ntawm cov tshuaj chloride concentration thiab lub sijhawm rau PTFE-crevice tsis ua haujlwm:

< 30 ppm chloride: No PTFE crevice failures recorded in 60 months.

30-80 ppm chloride: nruab nrab tsis ua haujlwm 28 lub hlis (ntau 18-48 lub hlis).

80-150 ppm chloride Median tsis ua hauj lwm 12 lub hlis Range 6-24 lub hlis.

150-300 ppm chlorine Median tsis ua hauj lwm 4 lub hlis Range 2-8 lub hlis

Qhov kev cuam tshuam zoo yog tias PTFE cov khoom txhawb nqa yog qhov tsis muaj zog tshaj plaws nyob rau hauv lub rhaub dej sib dhos hauv ntau qhov dej hauv nroog (feem ntau 20-100 ppm chloride), txawm tias cov tshuaj chloride ntau yuav qhia tias 316 stainless hlau yuav tsum txaus rau 5-10 xyoo.

Tsim Kev Hloov Kho kom tshem tawm qhov teeb meem PTFE Crevice
Ntxiv nrog rau kev tsim lub tank yooj yim, muaj ntau yam kev coj ua uas tuaj yeem ua haujlwm kom txo qis crevice corrosion nyob rau hauv kev txhawb nqa brackets. Txoj kev ua tau zoo tshaj plaws hloov cov khoom siv ntawm lub bracket, geometry ntawm lub installation lossis qhov zoo ntawm lub plhaub ntawm qhov chaw sib cuag.

Ua ntej, hloov PTFE brackets nrog cov pa permeable lossis cov khoom ntxeem tau kiag li. Nyob rau hauv EPDM ua npuas ncauj roj hmab txhawb txoj kev rau oxygen diffusion yog qhib los ntawm cov polymer matrix, thiaj li hais tias ib tug zoo muaj peev xwm yog khaws cia nyob rau hauv cov hlau nto txawm nyob rau hauv compression. Kev ntsuam xyuas ntawm PTFE vs. EPDM ua npuas ncauj brackets ntawm 316 sheaths nyob rau hauv 150 ppm chloride dej ntawm 75℃qhia tau hais tias EPDM- nruab cov cua sov qhia tias tsis muaj crevice pitting tom qab 2000 teev, tab sis PTFE - nruab cov cua sov tsim 0.5 hli 0 teev nyob rau hauv.

Qhov thib ob, rov tsim kho cov hlua khov kho nrog cov kav dej. Lub PTFE thaiv yuav tsis tas mus li tab sis yuav muaj peb - taw tes tiv tauj ncoo (txhua lub ncoo 3-5 hli dav) nrog 5 hli ntu nruab nrab ntawm. Qhov ntev ntawm kev sib cuag nrog lub sheath yuav tsum yog 20-40 mm. Cov qhov khoob tso cai rau cov dej ntws thiab cov pa oxygen mus rau qhov chaw nyob. Qhov kev ntsuam xyuas qhia tau hais tias peb lub ncoo bracket tsim minimizes qhov tob ntawm crevice corrosion los ntawm 80% piv rau cov khoom sib cuag bracket.

Thib peb, qhia kom muaj thermally sprayed aluminium txheej ntawm lub sheath ntawm lub bracket contact sites. Qhov no yog vim lub 0.1-0.2 hli txhuas txheej uas yuav nyiam corrode thiab muab ib tug sacrificial anode los tiv thaiv lub hauv paus ntawm 316 stainless hlau. Kev ntsuas nrawm hauv 200 ppm chloride ntawm 80℃qhia pom cov ntsiab lus txhuas coated tiv tauj tsis muaj 316 pitting tom qab 3000 teev. Uncoated tswj tsis pub dhau 500-800 teev.

Plaub, yog tias koj muaj PTFE brackets uas twb muaj lawm uas tsis tuaj yeem hloov kho, tso lub siab kub polysulphide sealant lossis silicone gasket ntawm lub bracket thiab sheath. Lub sealant nkaus ntsaws lub fissure, tshem tawm cov dej ingress thiab qhov sib txawv aeration cell. Tab sis txoj kev no yuav tsum tau ceev faj txog kev siv thiab kev soj ntsuam raws sij hawm raws li lub sealant yuav deteriorate nyob rau lub sij hawm thiab rov-tsim lub crevice.

Cov lus qhia tshwj xeeb rau kev txhawb nqa cua sov, Corrosion Resistant
Thaum muab 316 stainless hlau hluav taws xob cua sov raj rau cov dej kub cia siv PTFE lossis lwm yam khoom siv polymer, cov kws ua haujlwm yuav tsum suav nrog cov kev cai hauv qab no hauv kev yuav khoom. Rau cov tshuaj chloride ntau dua 50 ppm, xav kom cov khoom siv bracket yuav tsum yog cov pa oxygen -permeable polymer (xws li, EPDM ua npuas ncauj), los yog lub bracket yuav tsum muaj cov kav dej ntawm qhov tsawg kawg nkaus 2 mm dav, spaced ntawm lub ncua sij hawm tsis pub tshaj 10 mm, los yog sheath nto ntawm tag nrho cov ntsiab lus ntawm kev sib cuag yuav tsum tau muab nrog ib tug tuab ntawm 1 hli los yog zinc. Rau cov tso tsheb hlau luam uas xav kom muaj cov tshuaj chloride ntau dua 150 ppm, pom zoo kom tshem tawm tag nrho cov kev txhawb nqa polymer los ntawm kev siv cov sheaths nrog kev sib koom ua ke welded standoffs (316 stainless hlau projections tawm ntawm lub ntsiab raj) los yog upgrade cov ntaub sheath rau super- austenitic alloy 254 SMO los yog welded 2 cov kev tshawb fawb los ntawm titanium Field. Lub neej nruab nrab ntawm lub tshuab cua sov ntau tshaj 8 xyoo hauv cov dej uas muaj 200-300 ppm chloride, piv rau 4-8 lub hlis rau PTFE-bracketed designs hauv tib qhov kev pabcuam. Pom tau tias qhov teeb meem tsis yog 316 stainless hlau, tab sis qhov tawg tshwm sim los ntawm qhov tsis zoo ntawm PTFE bracket, engineers tuaj yeem hais kom yooj yim thiab qis tus nqi tsim kho kom tshem tawm cov kev ua tsis tiav feem ntau hauv kev lag luam kub dej rhaub.