Qhov siab tshaj plaws Chloride Concentration tuaj yeem 316 Stainless Hlau Sheathed Rhaub Nrog rau hauv nruab nrab pH Dej ntawm 90℃yam tsis muaj Pitting hauv 5 xyoos

Chloride Threshold rau Kev Siv Dej Kub 5 Xyoo Kev Pabcuam Lub Neej

Qhov siab tshaj plaws tso cai chloride concentration uas yuav tso cai rau 5- xyoo kev pab cuam lub neej yam tsis muaj pitting perforation ntawm 316 stainless hlau sheathed hluav taws xob cua sov raj rau hauv nruab nrab pH (6.5-}8.0) dej ntawm 90℃-ib yam mob rau industrial kub tank, tsis muaj nqi sib pauv. Nws nyob ntawm qhov chaw tiav, phab ntsa thickness thiab muaj cov crevices. Kev sim rau hauv chav sim thiab cov ncauj lus kom ntxaws txog kev ua tsis tiav tau pom tias 316 sheath nrog electropolished tiav thiab 1.5 hli phab ntsa thickness yuav muaj sia nyob rau tsib xyoos ntawm cov tshuaj chloride txog li 1000 ppm hauv cov dej zoo oxygenated thiab kev ua haujlwm tsis tu ncua ntawm lub rhaub. Cov ntaub ntawv zoo tib yam nrog cov pob zeb ua tiav hauv 12-18 lub hlis ntawm 500 ppm chloride. Daim ntawv no suav cov tshuaj chloride txwv rau 316 sheaths nyob rau hauv cov xwm txheej kub kub kev pab cuam, muab kev txiav txim siab matrix rau saum npoo thiab kev khiav hauj lwm hom, thiab txhais tau tias qhov pib thaum yuav tsum tau upgrade rau 316L los yog duplex stainless hlau.

Lub Critical Chloride Concentration thiab Pitting Mechanism

Pitting corrosion ntawm 316 stainless hlau nyob rau hauv kub nruab nrab chloride daws tshwm sim thaum cov tshuaj chloride concentration ntawm cov hlau nto tshaj qhov tseem ceeb uas yuav tsum tau mus ua txhaum cov passive zaj duab xis. Rau tag nrho annealed 316 nrog ib tug du, passivated nto, qhov tseem ceeb chloride concentration ntawm 90℃yog nyob rau hauv qhov kev txiav txim ntawm 1,200-1,500 ppm nyob rau hauv tas li immersion tsis muaj fissures. Pits tuaj yeem pib qis dua qib no tab sis yuav rov ua dua ua ntej kev txhim kho dhau qhov loj me. Nyob rau theem no, cov pits ruaj khov loj hlob ntawm 0.2-0.5 hli / xyoo, xuas nrig ntaus los ntawm 1.5 hli phab ntsa hauv 3-7 xyoo, nyob ntawm qhov tseeb chloride concentration thiab qhov chaw saum npoo. Tab sis cov cua sov tiag tiag hauv thaj teb tsis tshua muaj nyob ntawm qhov chaw kuaj pom zoo. Deg roughness ua rau muaj kev nce ntxiv ntawm cov tshuaj chloride zoo nyob rau hauv qab ntawm cov kwj deg, raws li qhov tshwm sim ntawm lub zos acidification mechanism. Lub tshuab polished nto Ra=0.4 rau 0.8 µm txo qhov pib mus rau 800 rau 1,000 ppm. Ib qho kev ua tiav zeb tiav (Ra{22}} µm) nce qhov pib mus rau 400-600 ppm. Crevices nyob rau hauv mounting flanges, gaskets los yog scale deposits txo qhov pib mus rau 200-300 ppm, tsis hais txog ntawm lub nto tiav.

Quantified chloride txwv rau 5 xyoo pitting dawb kev pabcuam ntawm 90 degree

Ntev -ntev immersion thwmsim (5 xyoo ntev) ntawm 316 sheaths ntawm 1.5 mm phab ntsa thickness nyob rau hauv aerated nruab nrab dej ntawm 90℃yog summarized nyob rau hauv cov lus hauv qab no. Cov txiaj ntsig sawv cev rau qhov siab tshaj plaws chloride concentration uas tsis ua rau pitting nkag siab dua 0.3 hli (20% ntawm phab ntsa thickness) tsawg dua 5% ntawm cov qauv kuaj. Nyob rau hauv cov ntaub ntawv ntawm kev ua hauj lwm sib quas ntus (txog txhua hnub kub) cov ntsiab lus chloride tso cai yog nyob ib ncig ntawm 30% qis dua vim repassivation yog cuam tshuam los ntawm thermal cycling.

Nto Finish Condition Phab Ntsa Thickness (mm) Cov tshuaj chloride siab tshaj plaws rau 5-xyoo lub neej (ppm, kev ua haujlwm tas mus li) Cov tshuaj chloride siab tshaj plaws rau 5-xyoo lub neej (ppm, kev ua haujlwm tsis sib xws, 1 lub voj voog / hnub) Qhov chaw loj Pitting yuav ua li cas yog tias dhau lawm
Electropolished (Ra ≤0.15 µm) 1.5 1200 850 Random on surface of sheathUpgrade to 316L or duplex ( >1500 ppm)
Electropolished (Ra Tsawg dua lossis sib npaug ntawm 0.15 μm) 2.0 1500 1050 Random Txais tau txog 2000 ppm nrog phab ntsa tuab
Fine mechanically polished (Ra 0.2-0.4 um) 1.5 950 650Nto scrapes lossis inclusions Upgrade rau saum 1000 ppm
Fine mechanically polished (Ra 0.2-0.4 µm) 2.0 1200 800 Txais nrog phab ntsa tuab txog 1500 ppm
Txheem zeb tiav (Ra 0.8-1.2 µm) 1.5 550 380 Ntev kab kos tsis haum rau saum 600 ppm
2.0 700 490 Txheem zeb tiav (Ra 0.8-1.2 µm) Marginal saum 700 ppm txawm tias muaj phab ntsa tuab
As-drawn rough finish (Ra >1.2 µm) 1.5 350 250Txhua qhov chaw tsis pub> 400 ppm
Txhua qhov ua tiav, tawg hauv qab nplai / gasket1.5-2.0 250 175 Crevice areaupgrade rau titanium los yog tshem tawm ntawm crevice
chloride Threshold: Dab tsi nce lossis qis dua

Peb qhov tseem ceeb ntxiv cuam tshuam rau cov tshuaj chloride hauv lub rooj. Thawj yog cov dej ntws nrawm. Rau qhov xwm txheej tsis txaus lossis qis qis (qis dua 0.3 m / s) cov tshuaj chloride concentration polarization ntawm lub plhaub saum npoo yog txo los ntawm 30-40%. Kev nrawm nrawm (tshaj li 1.5 m / s) tsis tu ncua tshem tawm cov tshuaj chloride ciam ciam txheej thiab tuaj yeem nce qhov pib los ntawm 20-25% tsuav yog tias kev yaig-corrosion tsis tshwm sim. Qhov thib ob yog qhov concentration ntawm yaj oxygen; Cov dej aerated tag nrho (8-10 ppm O 2 ntawm 20 degree, txog 4-5 ppm ntawm 90 degree) muab cov tshuaj tiv thaiv cathodic tsim nyog rau kev ruaj ntseg passivity. Cov dej tsis huv (<0.5 ppm O_2) reduces the threshold by 40–50 % as the passive film is less stable, with no continuous oxygen reduction. The third criterion is the presence of sulphate or bicarbonate ions. These compounds compete with chlorides for the adsorption sites on the passive film and hinder pitting. Water containing 200-500 ppm sulphate can withstand 1.5-2.0 times the chloride concentration before initiation of pitting.

Tswv yim Spec rau 316 Cua sov rau 90 deg C Dej Kev Pabcuam

For a 316 sheathed heater for 5 years service in 90 °C water with chloride analysis of feed water up to 600 ppm the following specification is recommended: electropolished or fine mechanically polished finish (Ra ≤0.4 µm), minimum wall thickness of 1.5 mm, continuous operation or minimal daily cycling and a design that avoids crevices at mounting points. For chloride levels from 600 to 1,000 ppm, upgrade to 2.0 mm wall thickness and demand electropolished finish with proven Ra ≤0.15 µm. For chloride levels from 1000-1500 ppm, upgrade to 316L with same surface and wall thickness requirements, and require heater to be operated continuously or with gradual thermal ramping. Do not use 316 and 316L for chloride levels >1500 ppm ntawm 90 degree. Qhia meej duplex 2205 los yog titanium sheaths. Kev saib xyuas cov ntsiab lus chloride yog qhov tseem ceeb vim tias qhov concentration ntawm 2-5 npaug ntawm cov khoom noj uas tuaj yeem ua tiav los ntawm evaporation hauv cov tso tsheb hlau luam qhib.

Xaus: Tsim kom muaj 5-Xyoo Chloride Threshold rau Kev Pabcuam Zoo

Lub 316 stainless hlau encased rhaub yuav tsis pit nyob rau hauv nruab nrab pH dej ntawm 90℃rau 5 xyoo ntawm chloride concentrations ntawm 350 ppm rau ib tug ntxhib, raws li - kos tiav rau 1200 ppm rau ib tug electropolished tiav. Cov kws kho tsheb yuav tsum txheeb xyuas cov dej chemistry (qhov phem tshaj -qhov xwm txheej ntawm cov tshuaj chloride), qhov ua tiav ntawm qhov chaw thiab phab ntsa tuab yuav tsum tau ua. Siv cov kev txwv kom muaj nuj nqis hauv cov lus saum toj no, Cov neeg yuav khoom tuaj yeem xaiv 316 sheaths uas muab 5-xyoo kev pabcuam hauv kev pabcuam dej kub thiab zam kev ua tsis tiav pitting ntxov uas tshwm sim thaum cov tshuaj chloride ntau tshaj qhov txwv rau qhov chaw xaiv.