Pitting corrosion yog ib qho kev puas tsuaj thiab nyuaj tshaj plaws -kom- kuaj xyuas cov hlau degradation. Tsis zoo li cov corrosion tsis sib xws uas kis tusyees hla ib qho chaw, pitting tawm tsam me me, thaj chaw hauv cheeb tsam thaum cov hlau nyob ib puag ncig tseem tsis cuam tshuam. Qhov no ua rau nws muaj kev phom sij tshwj xeeb- cov yeeb nkab tuaj yeem ua lub suab zoo kawg nkaus los ntawm sab nraud thaum lub qhov me me loj hlob tob rau hauv phab ntsa, thaum kawg ua rau cov dej xau lossis kev puas tsuaj loj nrog kev ceeb toom me ntsis.
Rau cov engineers, chaw tswj xyuas, thiab cov neeg cog lus ua lub luag haujlwm rau cov kav dej, kev nkag siab pitting corrosion yog qhov tseem ceeb. Phau ntawv qhia no piav qhia txog dab tsi ua rau pitting, yuav ua li cas paub txog nws ua ntej tsis ua haujlwm, thiab qhov tseem ceeb tshaj, cov kauj ruam twg koj tuaj yeem ua los tiv thaiv nws hauv koj lub cev.
Pitting Corrosion yog dab tsi?
Pitting corrosion yog ib hom kev tawm tsam hauv zos uas tsim cov qhov me me lossis kab noj hniav hauv cov hlau. Cov pits no feem ntau pib ntawm qhov tsis sib xws ntawm qhov chaw- khawb, suav nrog, lossis thaj chaw uas cov txheej tiv thaiv oxide tau tawg. Thaum pib, lub qhov dej tsim cov tshuaj lom neeg ib puag ncig hauv nws tus kheej. Hauv qab ntawm lub qhov dej yuav depleted ntawm oxygen thaum ua enriched nrog chloride ions thiab acidic corrosion khoom. Qhov no ua rau corrosion sai ntawm lub qhov hauv qab, ua rau nws loj hlob tob dua li qhov dav.
Qhov tshwm sim yog qhov me me qhov qhib zais qhov kab noj hniav loj dua hauv qab. Nyob rau hauv qhov xwm txheej hnyav, lub qhov dej tuaj yeem nkag mus rau hauv cov yeeb nkab phab ntsa tag nrho thaum qhov chaw nyob ib puag ncig pom tias tsuas yog muaj xim me me xwb.
Cov ntaub ntawv uas pheej hmoo
Txawm hais tias txhua yam hlau tuaj yeem ua rau hauv qhov tsis raug, qee cov ntaub ntawv muaj kev cuam tshuam ntau dua li lwm tus:
Stainless hlau: Tshwj xeeb yog yooj yim nyob rau hauv ib puag ncig chloride. Cov qib txheem zoo li 304 thiab 316 tuaj yeem ua rau lub qhov dej thaum raug dej ntsev, tshuaj dawb, lossis qee yam tshuaj lom neeg.
Aluminium thiab nws cov alloys: Ib txwm tiv taus vim oxide zaj duab xis, tab sis chlorides ua rau cov yeeb yaj kiab no thiab pib pitting.
Copper thiab tooj liab alloys: Muaj kev cuam tshuam rau hauv qee yam dej chemistry, tshwj xeeb tshaj yog siab -chloride lossis qis- pH.
Cov pa roj carbon steel: Feem ntau corrodes ntau uniformly, tab sis tuaj yeem pom pitting nyob rau hauv ib puag ncig zoo li cov av nrog sib txawv aeration.
Yuav ua li cas txheeb xyuas Pitting Corrosion
Kev tshawb nrhiav thaum ntxov yog qhov nyuaj tab sis tseem ceeb. Nov yog dab tsi los nrhiav:
Visual Indicators
Cov kab me me los yog staining ntawm qhov chaw uas tsis so
Cov qhov me me los yog kab noj hniav, qee zaum nrog cov khoom siv crystalline lossis hmoov corrosion nyob ib ncig ntawm lub npoo
Discoloration los yog tubercles (nce mounds ntawm corrosion khoom) npog lub qhov tiag tiag
Performance Indicators
Unexplained siab poob rau hauv lub system
Nquag xau ntawm qhov chaw tshwj xeeb thaum lwm ntu tseem nyob twj ywm
Particulates los yog discoloration nyob rau hauv lub kwj dej
Kev tshuaj xyuas
Dye penetrant testing: Ib qho dye yog siv rau ntawm qhov chaw thiab kos rau hauv qhov pits los ntawm capillary nkaus, qhia lawv qhov chaw.
Kev kuaj ultrasonic: ntsuas cov phab ntsa tuab thiab tuaj yeem ntes cov pits sab nraud ua ntej lawv nkag mus.
Eddy kev sim tam sim no: Siv tau rau cov uas tsis yog - ferrous raj zoo li tooj liab thiab stainless hlau, kuaj cov pits thiab tawg.
Kev kuaj pom hluav taws xob: X-ray lossis gamma-ray kuaj pom pom sab hauv pitting hauv cov kav dej thiab cov hlab ntsha.
Lub hauv paus ua rau Pitting Corrosion
Kev nkag siab yog vim li cas pitting tshwm sim pab tiv thaiv nws. Feem ntau ua rau muaj xws li:
Chlorides thiab Halides
Chloride ions yog cov yeeb ncuab tseem ceeb ntawm stainless hlau. Lawv nkag mus thiab rhuav tshem cov yeeb yaj kiab oxide tiv thaiv ntawm cov ntsiab lus tsis muaj zog, pib qhov pits. Cov tshuaj chlorides muaj nyob rau hauv dej hiav txwv, txoj kev ntsev, tshuaj dawb, ntau yam khoom siv tshuaj, thiab txawm tias qee cov dej hauv nroog.
Cov xwm txheej tsis zoo
Cov dej ntws pab tswj cov qib oxygen tsis sib xws thiab tshem tawm cov khoom siv corrosive. Cov dej tsis tu ncua tso cai rau cov hlwb sib txawv los tsim, qhov twg cov pa oxygen-depleted thaj chaw ua anodic thiab tsav pitting.
Kub
Kev kub siab dua ua kom cov tshuaj tiv thaiv electrochemical tsav pitting. Stainless hlau uas ua tau zoo nyob rau hauv cov tshuaj chloride txias yuav pit sai heev thaum tib tov yog rhuab.
Qhov Defects
Kos, burrs, weld discoloration, thiab inclusions ua raws li qhov chaw pib. Weld zoo tsis zoo, nkag mus tsis tiav, thiab tsis muaj kev tshaj tawm -welding tu yog ib qho kev koom tes.
Kev ua ntawm microbial
Microbiologically influenced corrosion (MIC) tshwm sim thaum cov kab mob tsim cov cheeb tsam hauv cheeb tsam uas txhawb nqa pitting. Sulfate-txo cov kab mob, feem ntau hauv dej thiab av, yog qhov ua txhaum ntau zaus.
Galvanic teebmeem
Kev sib txuas cov hlau tsis sib xws tuaj yeem ua rau muaj kev cuam tshuam hauv cheeb tsam ntawm cov khoom siv tsis zoo nyob ze ntawm kev sib tshuam.
Cov tswv yim tiv thaiv
Tiv thaiv pitting corrosion yuav tsum tau ua tib zoo xaiv cov khoom siv, tsim qauv, tsim kom zoo, thiab kev ua haujlwm.
1. Xaiv cov khoom zoo
Rau cov tshuaj chloride- muaj ib puag ncig, tus qauv 304 stainless hlau feem ntau tsis txaus. Xav txog cov kev hloov kho tshiab no:
316 / L stainless hlau: muaj molybdenum (2-3%), txhim kho cov tshuaj chloride zoo.
Duplex stainless hlau (2205, 2507): Muab cov pitting zoo heev ua ke nrog lub zog siab.
Super austenitic stainless hlau (6% Mo qib): Tsim tshwj xeeb rau kev siv tshuaj chloride txhoj puab heev.
Titanium: Zoo tiv thaiv chloride pitting, txawm tias kim.
Tus Pitting Resistance Equivalent Number (PREN) muab qhov sib piv: PREN=%Cr + 3.3(%Mo) + 16(%N). Cov lej siab dua qhia tias muaj kev tiv thaiv zoo dua.
2. Tswj ib puag ncig
Tswj kev khiav dej num: Tsis txhob nyob twj ywm. Tsim kom ua tiav cov kua dej yog qhov ua tau.
Tshem tawm cov chlorides: Qhov twg ua tau, txo cov tshuaj chloride los ntawm kev kho dej.
Kev tswj qhov kub thiab txias: Kev ua haujlwm qis qis txo qhov kev pheej hmoo pitting.
Kev kho mob biocide: Hauv cov kab mob uas raug mob, kho dej los tswj MIC- ua rau cov kab mob.
3. Ua kom zoo Fabrication
Kev vuam zoo: Siv cov txheej txheem tsim nyog. Xyuas kom tag nrho nkag mus thiab huv si, oxide-dawb nto.
Tshaj tawm -welding tu: Tshem tawm cov cua sov thiab oxide txheej. Pickling thiab passivation restore corrosion kuj.
Smooth nto: Tsis txhob khawb thiab cov cuab yeej cim thaum tuav thiab teeb tsa.
Kev tuav cov khoom siv: Tiv thaiv cov ntaub ntawv los ntawm kev sib kis los ntawm cov pa roj carbon steel (cov hlau tuaj yeem pib pitting).
4. Xav txog kev tiv thaiv
Txheej: Rau cov pa roj carbon steel, siab - cov txheej txheem ua tau zoo cais cov hlau los ntawm ib puag ncig.
Kev tiv thaiv Cathodic: Nyob rau hauv faus los yog immersed daim ntaub ntawv, impressed tam sim no los yog txiab anodes tuaj yeem tiv thaiv pitting.
Inhibitors: Cov tshuaj inhibitors tuaj yeem muab ntxiv rau kaw- lub voj voog kom txo tau qhov corrosivity.
5. Ua raws li kev soj ntsuam
Corrosion daim coupon: Nruab daim coupons ntawm cov ntsiab lus tswv yim thiab tshuaj xyuas tsis tu ncua.
Kev ntsuam xyuas tsis muaj kev puas tsuaj: Teem caij UT lossis kev tshuaj ntsuam xyuas tam sim no ntawm cov kab tseem ceeb.
Kev kuaj dej: Saib xyuas cov qib chloride, pH, thiab cov kab mob ua haujlwm.
Piv txwv li: Stainless hlau hauv dej txias
Ib qho xwm txheej qhia txog cov ntsiab cai no. Ib qho chaw tau teeb tsa 304 stainless hlau piping rau qhov kaw - voj kaw dej txias. Tom qab ob peb xyoos, pinhole leaks tsim nyob rau hauv qab ntawm kab rov tav khiav.
Kev tshawb nrhiav tau qhia:
Low flow velocities cia stagnation ntawm cov ntsiab lus qis
Chlorides los ntawm thawj zaug sau dej concentrated los ntawm evaporation
MIC cov kab mob nyob hauv cov chaw xau
Kev daws yuav tsum tau:
Kev tshem tawm qhov system thiab kev kho biocide
Hloov kho mus rau 316L stainless rau cov seem hloov
Hloov ua haujlwm kom tswj tau ntws los ntawm txhua ceg
Kev kuaj dej tsis tu ncua thiab kev kho mob
Pitting Resistance Sib piv los ntawm cov khoom
|
Khoom siv |
PREN Ntau |
Chloride kam rau ua |
Tus nqi txheeb ze |
|
304/L |
18-20 |
Tsawg |
Lub hauv paus |
|
316/L |
23-28 |
Nruab nrab |
1.3-1.5x |
|
2205 Duplex |
32-35 |
Siab |
2-2.5x |
|
6% Mo Super Austenitic |
42-48 |
Siab heev |
3-4x |
|
2507 Super Duplex |
42-48 |
Siab heev |
3-4x |
|
Titanium Qib 2 |
N/A |
Zoo heev |
8-10x |
Xaus
Pitting corrosion tsis tshaj tawm nws tus kheej nrov nrov. Nws ua haujlwm ntsiag to, zais hauv qab ntawm qhov chaw, kom txog thaum thawj qhov xau tshwm. Txog thaum ntawd, kev puas tsuaj loj tau tshwm sim. Tus yuam sij rau kev tswj cov kev pheej hmoo pitting yog nyob rau hauv kev nkag siab txog koj qhov system ib puag ncig, xaiv cov khoom tsim nyog rau ib puag ncig ntawd, tswj kom zoo thaum tsim khoom, thiab saib xyuas cov xwm txheej hauv lub sijhawm.
Rau cov txheej txheem tseem ceeb uas tsis ua haujlwm tsis yog ib qho kev xaiv, kev nqis peev hauv qib siab dua - cov ntaub ntawv qib siab thiab kev tswj xyuas zoo tau them nyiaj rau nws tus kheej ntau zaus dhau los ntawm kev zam kom tsis txhob muaj sijhawm poob qis, kho kim, thiab teeb meem kev nyab xeeb.
Xav tau kev pab hais txog Pitting Corrosion hauv koj qhov System?
Peb pab neeg ua haujlwm ua haujlwm nrog engineers thiab cov neeg saib xyuas chaw txhua hnub los daws cov teeb meem corrosion. Txawm hais tias koj tab tom tsim cov txheej txheem tshiab los tiv thaiv cov xwm txheej hnyav lossis daws teeb meem tsis ua haujlwm hauv kev teeb tsa uas twb muaj lawm, peb tuaj yeem pab koj txheeb xyuas cov ntaub ntawv thiab kev coj ua kom ntev - kev ntseeg tau ntev.
Tiv tauj peb cov kws tshaj lij corrosion rau kev sab laj, los yog thov peb cov ntaub ntawv xaiv cov khoom siv rau chloride ib puag ncig.