To solve the problem that, in equipment using stainless steel, at the time when industrial fuming sulfuric acid and industrial concentrated sulfuric acid are diluted, and are used as dilute sulfuric acid of 3 to 20 mass%, the generation of black precipitated products and corrosion in the stainless steel occur in certain cases, and do not occur in the other cases, and, regarding the cause therefor, as the well known fact in the black precipitates and corrosion of stainless steel, the phenomenon that H2SO3 in the acid solution is spontaneously reduced to H2S in the surface of the stainless steel, so that the active dissolution of the stainless steel in an active region is remarkably promoted by H2S to cause severe corrosion is mentioned, and to prevent the corrosion of stainless steel caused by dilute sulfuric acid at a low cost.
Regarding the method of preventing corrosion in stainless steel on use of dilute sulfuric acid, the concentration of SO2 in dilute sulfuric acid of 3 to 20 mass% is held to >0 to 5 mass ppm. Regarding the method of preventing corrosion in stainless steel on use of dilute sulfuric acid, the concentration of SO2 in dilute sulfuric acid of 3 to 20 mass% is held to >0 to 12 mass ppm with an oxidizing agent.
YAMAKI TETSUO
KATSURA SHIGEO
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