Pitting thiab Crevice Corrosion Resistance ntawm Incoloy 925

1. Core Mechanisms ntawm Pitting thiab Crevice Corrosion Resistance

Cov ntsiab lus siab chromium (19.0–21.0 wt%): Chromium forms a dense, adherent and self-healing chromium oxide passive film on the alloy surface. Cov yeeb yaj kiab no ua raws li lub cev thiab tshuaj tiv thaiv, tiv thaiv ions corrosive (tshwj xeeb tshaj yog Cl⁻) los ntawm kev nkag mus rau hauv substrate thiab pib corrosion.

Molybdenum ntxiv (2.5-3.5 wt%): Molybdenum yog lub hauv paus tseem ceeb rau kev txhim kho hauv zos corrosion kuj. Nws koom nrog kev tsim cov yeeb yaj kiab passive, txhim kho zaj duab xis stability thiab compactness. Qhov tseem ceeb tshaj, molybdenum tuaj yeem cuam tshuam cov adsorption ntawm Cl⁻ ntawm cov hlau nplaum thiab tiv thaiv kev tawg ntawm cov yeeb yaj kiab tsis zoo los ntawm cov tshuaj chloride ion tsub zuj zuj.

Copper alloying (1.5-3.0 wt%): Copper txhim khu lub alloy qhov kev tiv thaiv kom tsis txhob muaj acidic ib puag ncig (xws li sulfuric acid, phosphoric acid media) thiab synergistically txhim kho cov stability ntawm passive zaj duab xis nyob rau hauv chloride - muaj cov ntaub ntawv sib xyaw.

Kev tswj nruj ntawm cov khoom tsis zoo: Raws li tau hais dhau los, qhov txwv qis ntawm C (Less dua lossis sib npaug li 0.03 wt%), S (Less dua lossis sib npaug li 0.015 wt%), thiab P (Less dua lossis sib npaug li 0.020 wt%) zam qhov tsim ntawm carbide precipitates, sulfide inclusions thiab lwm yam tsis xws luag. Cov teeb meem no yog qhov chaw pib qhov chaw rau pitting thiab crevice corrosion; tshem tawm lawv ua kom lub uniformity ntawm passive zaj duab xis thiab lub substrate qauv.

Precipitation strengthening microstructure: Tom qab kev kho cua sov tsim nyog (kev daws teeb meem + kev laus), cov hlau nplaum ua kom zoo 'theem (Ni₃(Ti, Al)) thiab carbides, uas txhim kho cov neeg kho tshuab lub zog yam tsis muaj kev cuam tshuam corrosion kuj. Kev faib tawm tsis sib xws ntawm precipitates zam microstructural heterogeneities uas tuaj yeem ua rau muaj kev cuam tshuam hauv zos.

2. Kev ua tau zoo nyob rau hauv Ib puag ncig Corrosive

Chloride{0}} muaj cov tshuaj aqueous: Hauv dej hiav txwv, ntsev pas dej brine, thiab cov dej txias ua haujlwm nrog cov tshuaj chloride siab, cov alloy tuav cov pitting zoo heev.

Rau Incoloy 925, tus nqi PREN feem ntau yog siab dua 35, uas yog ntau dua li cov hlau tsis zoo austenitic (xws li, 304 stainless hlau nrog PREN ≈ 18). Tus nqi PREN siab no qhia tias nws muaj peev xwm tiv taus pitting corrosion hauv chloride ib puag ncig.

Crevice corrosion scenarios: Nyob rau hauv cov xwm txheej xws li flange kev sib txuas, bolted pob qij txha, thiab cov pa hluav taws kub exchanger tube nplooj ntawv, qhov twg stagnant corrosive xov xwm yog nquag mus sau, Incoloy 925 qhia zoo crevice corrosion kuj. Cov kev ntsuam xyuas tau pom tias nyob rau hauv 3.5 wt% NaCl tov ntawm 60 degree, cov hlau tsis ua kom pom tseeb crevice corrosion txawm tias tom qab ntev - lub sij hawm immersion, thaum cov pa stainless hlau yuav raug kev txom nyem los ntawm crevice corrosion nyob rau hauv tib yam.

Roj thiab roj ntau lawm ib puag ncig: Nyob rau hauv qhov chaw ib puag ncig uas muaj H₂S, CO₂, thiab chloride ions (yog li- hu ua "kev pabcuam qaub"), cov hlau tiv thaiv pitting thiab crevice corrosion tshwm sim los ntawm kev sib xyaw ua ke ntawm corrosive gases thiab ions, ua rau nws tsim nyog rau kev tsim downhole tubulars, li qub, thiab cov khoom hauv lub taub hau.

Tshuaj ua cov xov xwm: Hauv xov xwm xws li sulfuric acid, phosphoric acid, thiab cov organic acids uas muaj chloride impurities, cov hlau muaj peev xwm tswj tau qhov kev ua haujlwm ruaj khov yam tsis muaj kev cuam tshuam hauv zos, uas yog siv rau cov tshuaj reactor internals, pipeline systems, thiab twj tso kua mis valve.

3. Cov yam ntxwv cuam tshuam rau Pitting thiab Crevice Corrosion Resistance