| 摘要 |
PURPOSE:To prevent the titled damage, by chemically prewashing nickel base alloy, then contacting with high temp. deration alkali soln. incorporated with gaseous hydrogen of a suitable partial pressure or a suitable quantity of hydrazine. CONSTITUTION:In circumstance, etc., in heat exchanger in which nickel base alloy such as 15 Cr - 75 Ni - Fe and high temp. dearation alkali soln. are contacted, prior to supplying the soln. contacting surface of the nickel alloy with the soln. is chemically washed to remove sludge such as Fe3O4, Fe2O3, CuO, etc., adhered on the surface. Further, gaseous hydrogen of >=10<-5> atm or/and >=1000 ppb hydrazine are added to the soln. to be supplied to prevent formation of oxidizable impurity. The chemical washing by liquid contg. aliphatic carboxylic acid such as citric acid, oxalic acid, formic acid and EDTA and adjusted to 5-6.5 pH by NH3 is suitable. In this way, raise of corrosion potential of the nickel base alloy to potential region causing grain boundary damage is prevented.
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