Corrosion Status and Failure Reason Analysis of Sewage Tanks in Domestic Refineries

The present situations of corrosion cracking of many sewage tanks and the composition of corrosive mediums in domestic refineries are statistically analyzed.It is found that nitrate is an important corrosive component that can cause stress corrosion.Based on the analysis of corrosion mechanism and corrosion products for different corrosive components,the following conclusions are drawn:the stress corrosion caused by hydrogen sulfide+ammonia+nitrate+water is the real reason for cracking and leakage of the sewage tanks,in which the stress corrosion caused by wet hydrogen sulfide is the main factor,the stress corrosion caused by ammonia and nitrate is secondary factor;and chloride ion has the effect of promoting wet hydrogen sulphide stress corrosion in alkaline environment.