20. Yuav ua li cas cov zinc txheej corrode nyob rau hauv cov dej txias?

Dej-pas galvanized steel kav (hu ua "Galvanized Welded Steel Pipes for Low-Pressure Fluid Transportation" in the new national standard GB3091-82) yog siv los ua cov kav dej. Yog li ntawd, nws yog ib qho tseem ceeb rau kev kawm txog tus cwj pwm corrosion ntawm zinc txheej hauv cov kais dej. Txhawm rau kom nkag siab txog cov txheej txheem corrosion no, peb yuav tsum ua ntej kuaj xyuas qhov muaj pes tsawg leeg ntawm cov kais dej. Feem ntau, 1 liter dej muaj 10 milligrams ntawm cov pa oxygen. Qhov no oxygen reacts nrog zinc txheej los tsim zinc hydroxide, uas tshwm sim raws li corrosive byproduct es tsis yog ib tug tiv thaiv txheej. Cov dej mos, uas muaj ntau dua cov pa oxygen, carbon dioxide, thiab sodium ntsev (los ntawm cov txheej txheem softening), ua kom cov zinc txheej corrosion. Hauv qhov sib piv, cov dej tawv muaj aluminium hydroxide, silicic acid, phosphates, magnesium ntsev, thiab calcium carbonate, uas tsim cov txheej tiv thaiv ntawm zinc txheej. Yog li ntawd, galvanized steel kav muaj qhov zoo dua corrosion kuj nyob rau hauv cov dej nyuaj piv rau cov dej mos.
Tus nqi pH ntawm cov kais dej feem ntau yog nyob rau hauv thaj tsam ntawm 7.5-9.5. Thaum cov calcium bicarbonate, sulfide, chloride thiab nitride nyob rau hauv cov ntsiab lus tso cai, zinc txheej yog nyob rau hauv ib qho chaw ruaj khov thiab tiv thaiv vim yog tsim ntawm insoluble carbonate txheej.
Cov dej kais dej yog kho nrog kua chlorine rau kev tua kab mob, uas yog corrosive heev rau zinc txheej. Thaum zinc txheej muaj cov tin ntau tshaj 0.28%, lawv tuaj yeem tsim pitting corrosion hauv cov kais dej. Yog li ntawd, kub -dip galvanized steel kav siv rau dej yuav tsum tsis txhob txhob txwm muab tin rau hauv lawv cov txheej. Feem ntau, cov tin- dawb zinc coatings corrode ntawm tus nqi kwv yees li ntawm 0.66 mg / dm²·d hauv dej txias, thaum tin- muaj zinc txheej corrode ntawm tus nqi kwv yees li 2.03 mg / dm²·d.