Nyob rau hauv dab tsi tshwj xeeb kev sib xyaw ntawm Dissolved Oxygen Level thiab Flow Velocity Puas 316 Stainless Steel Heater Sheath Hloov los ntawm Passive mus rau Erosion-Corrosion nyob rau hauv siab-Tsev Dej

Mechanical tshem tawm cov zaj duab xis passive raws li ib tug tsis ua hauj lwm mechanism

Erosion-corrosion ntawm hluav taws xob cua sov raj sheathed hauv 316 stainless hlau thiab raus hauv dej kub (80-100 degree) uas muaj cov khib nyiab tshem tawm lossis ua haujlwm ntawm qhov nrawm nrawm. Cov yeeb yaj kiab tsis zoo yog qhov tsis zoo lossis kev tshem tawm los ntawm kev yaig -corrosion nyob ntawm kev sib xyaw ntawm cov pa oxygen yaj thiab cov dej tshaj tawm. Cov txheej txheej passive re- cov ntaub ntawv sai li sai tau thaum nws raug tshem tawm thiab cov nqi corrosion qis dua 0.05 hli ib xyoos nyob rau hauv qhov tseem ceeb. Tshaj li qhov tseem ceeb, tus neeg kho tshuab tshem tawm tus nqi tshaj qhov repassivation tus nqi thiab cov hlau poob yog ceev mus rau 1 mus rau 5 mm / xyoo, txaus perforate ib phab ntsa 1.5 mm tuab nyob rau hauv 3 mus rau 18 lub hlis. Daim ntawv no kwv yees cov pa oxygen yaj- nrawm nrawm rau qhov pib yaig-corrosion pib ntawm 316 sheaths thiab nthuav tawm cov dej dynamics tsim cov lus qhia rau kev pabcuam txhim khu kev qha.

Mechanism ntawm Electrochemical-Mechanical Coupling

Kev yaig corrosion ntawm 316 stainless hlau hauv dej yuav tsum muaj peb yam: cov kua dej ntws los ntawm cov hlau saum npoo los tsim cov kev ntxhov siab shear, txaus yaj cov pa oxygen los txhawb nqa kev ua haujlwm cathodic, thiab tshem tawm cov khoom abrasive lossis siab - npuas npuas uas tuaj yeem cuam tshuam cov zaj duab xis passive. Nyob rau hauv cov dej huv, nrog lub siab tshaj tawm thiab tsis muaj cov khoom, cov zaj duab xis passive tuaj yeem nyob twj ywm raws li cov shear quab yuam ib leeg (txog 10-20 Pa) tsis tshaj cov zaj duab xis adhesion zog. Txawm li cas los xij, ntawm li 2 ppm yaj cov pa oxygen repassivation tus nqi poob thiab txawm tias me me shear kev nyuaj siab tuaj yeem tiv thaiv kev tsim cov yeeb yaj kiab ruaj khov. Ntawm qhov tod tes, nrog cov ntsiab lus oxygen siab (tshaj 5 ppm) repassivation yog ceev thiab cov yeeb yaj kiab tuaj yeem tiv taus ntau dua. Cov xwm txheej phem tshaj plaws yog nyob nruab nrab ntawm cov pa oxygen (0.5-2 ppm) qhov twg repassivation yog maj mam tab sis muaj txaus cathodic tam sim no los txhawb anodic dissolution ntawm txhua qhov chaw hlau liab qab.

Quantified Erosion-Corrosion Thresholds 316 ntawm 90C

Flow voj thiab rotating lub tog raj kheej electrode kuaj nrog 316 stainless hlau cov qauv hauv 90℃dej (pH 7.5, 100 ppm chloride) tau txiav txim siab qhov nrawm nrawm thiab yaj cov pa oxygen sib xyaw ua ke uas ua rau yaig -corrosion tus nqi siab tshaj 0.1 hli hauv ib xyoos.

Dissolved Oxygen (ppm) Flow Velocity (m/s) Suspended Solids (ppm, 50 µm silica) Erosion-Corrosion Rate (mm/xyoo)|Lub Sijhawm rau Perforation (1.5 hli phab ntsa) Mechanism Pom zoo<0.05 >30 years Passive Yes >5 3-5 0 0.05-0.10 15-30 years Marginal Acceptable >5 5-8 0 0.10-0.25 6-15 years Transition Monitor >5 >8 0.25-0.50 3-6 xyoo Erosion-corrosionTsis pom zoo
2-5 <2 0.05-0.10 15-30 yearsAcceptable Yes 2-5 2-4 0 0.10-0.20 7-15 years MarginalAcceptable on inspection
2-5 4-6 0.20-.40 4-7 xyoo Erosion-CorrosiveTsis pom zoo rau lub sijhawm ntev
1-2 <1 0 0.10-0.20 7-15 yr.Instability of passive filmAcceptable with low chloride
1-2 1-2 0 0.20-0.50 3-7 yearsMixed tswj Tsis pom zoo
0.5-1 <0.5 0 0.15-0.30 5-10 yearsLow oxygen corrosion Marginal 0.5-1 >0.5 0 0.30-1.00 1.5-5 xyoo Erosion corrosion tsis kam txais<0.5 Any 0 >0.50 <3 years Active corrosion (deaerated) Unacceptable >5 2-3 100 0.15-0.30 5-10 xyoo Particle erosion Txais tau ntawm qis tshaj tawm 5 3-5 100 0.30-0.70 2-5 xyoo Kev yaig siab Tsis pom zoo5 5-8 100 0.70-2.00 1-2 xyoo Txais Tsis Tau
Npuas Impingement thiab Suspended Solids Effects

Cov khib nyiab tshem tawm txo qhov kev yaig -corrosion velocity threshold. Ntawm qhov nrawm nrawm li 2-3 m / s, dej nrog 100 ppm ntawm cov tawv tawv, cov khoom angular (xws li xuab zeb lossis silica) tuaj yeem ua rau cov yeeb yaj kiab tsis zoo ntawm 316 uas ua rau cov hlau poob 3-5 npaug ntau dua li cov dej huv ntawm tib qhov nrawm. Qhov teeb meem kev puas tsuaj tshaj plaws rau cov cua sov sheaths tsis yog qhov sib xws tab sis kev cuam tshuam hauv cheeb tsam ntawm khoov, lub luj tshib lossis cov dej ntws ntawm cov thermowells qhov twg cov dej nrawm nrawm thiab cov khoom tawm tsam ntawm qhov chaw. Cov npuas roj (los ntawm cavitation lossis flashing) zoo ib yam ua rau kev puas tsuaj. Yog tias daim ntawv thov tau paub cov khoom raug tshem tawm, qhov siab tshaj plaws tau pom zoo tshaj tawm rau 316 sheaths poob rau 1.5-2.0 m / s tsis hais txog qib oxygen yaj.

Tswv yim tsim kev pom zoo rau High Flow Service

Three design solutions prevent erosion-corrosion for 316 encased heaters in high-flow water systems (pumped circulation loops, heat exchangers, and cooling towers). The first method is to place the heater in a flow bypass or stilling well to reduce the local velocity at the sheath to less than 1 m/s while maintaining bulk flow in the main pipe. The second is to place the heater parallel to flow (axial alignment) rather than perpendicular, so that the drag force and shear stress are reduced by a ratio of 5-10. The third is to specify a thicker sheath wall (2.0 to 2.5 mm) to offer more corrosion allowance but this does not prevent initiation of erosion corrosion. If high velocity (>3 m / s) thiab qis yaj oxygen (< 2 ppm) are unavoidable in the system, then duplex 2205 stainless steel or Alloy 625 should be considered for upgrade.

Field Recognition of Erosion-Corrosion Damage

Nto cov yam ntxwv ntawm kev yaig-corrosion ntawm cov cua sov hauv siab- cov kev pabcuam ntws txawv ntawm cov pitting lossis crevice corrosion. Qhov chaw puas lawm feem ntau yog du, polished los yog 'dej-txiav' saib, feem ntau nrog cov grooves ncaj qha mus rau qhov kev taw qhia ntws (horseshoe lossis comet- zoo li lub qhov). Hlau poob yog kis tawm thoob plaws cheeb tsam puas, es tsis txhob ntawm ib lub qhov concentrated. Thiab ntawm qhov kev nthuav dav siab, qhov chaw nthuav tawm cov yas deformation thiab hlau smearing, tsis yog crystallographic facets ntawm SCC los yog lub voj voog pits ntawm chloride pitting. Kev yaig-corrosion yuav tsum tau xav tias yog lub rhaub dej tau ua haujlwm ntau dua 1-2 xyoos hauv dej nrog qhov nrawm dua 3m / s thiab yaj oxygen tsawg dua 2 ppm. Txhawm rau hloov, qhov khiav nrawm ntawm lub rhaub dej yuav tsum tau ntsuas thiab txo qis kom nyob hauv thaj chaw nyab xeeb hauv cov lus saum toj no.

Xaus: tswj kev khiav thiab oxygen rau 316 sheath kev ntseeg tau

Erosion-corrosion ntawm 316 stainless hlau encased rhaub nyob rau hauv high kub kev pab cuam dej pib thaum lub khiav ceev thiab yaj cov pa oxygen tsis txaus tso cai rau tsim ib tug ruaj khov passive txheej. Hauv cov dej huv uas muaj cov pa oxygen ntau tshaj 5 ppm, kev khiav ceev txog li 5 m / s raug tso cai. Qhov siab tshaj plaws ntawm cov pa oxygen 2-5 ppm poob rau 3-4 m / sec. Cov hlau poob tshwm sim ntawm qhov nrawm ntawm qhov nrawm tshaj 1 m / sec ntawm cov pa oxygen hauv qab 2 ppm. Cov khoom raug tshem tawm qis dua tso cai tshaj tawm los ntawm qhov ua tau ntawm 2 mus rau 3. 316 Rau qhov nrawm nrawm, yaj cov pa oxygen nyeem ntawv thiab piv rau cov pib qhia hauv cov lus saum toj no, cov sheaths tsim los rau cov twj tso kua mis yuav tsum tau ntsuas hauv zos lossis suav ntawm qhov cua sov. Txoj hauv kev uas tau hais los saum no ua rau cov neeg yuav khoom tsim cov dej ntws uas txhawb nqa cov txheej txheem passive thiab zam kom tsis txhob ntxov ntxov ntawm phab ntsa thinning, los ntawm kev cuam tshuam cov pa oxygen yaj, tshaj tawm thiab cov khoom thauj mus rau ntau qhov kev yaig-corrosion tus nqi.