DEW POINT CORROSION CRACKING OF LOW CARBONSTEELS AND THEIR WELD SEAMS IN NITRATE SOLUTIONS
低碳钢及焊缝硝酸盐露点腐蚀开裂研究

Recently,dew point corrosion cracking has been found in catalytic cracking equipments in many refineries.The reasons are thought to be the joint actions of welding residual stress and the gaseous corrosive media of nitrogen oxides,sulphur oxides,water vapor etc.which condensed on the wall of catalytic cracking equipments.In this paper,the susceptibility to stress corrosion cracking (SCC) of steels of 20G,16MnR,Q235-A and their weld seams were studied in various NH\-4NO\-3 solutions by the U-shaped constant strain method.Based upon experiments the effect of sulphur oxides on the susceptibility to SCC and the cracking mechanism of nitrate dew point corrosion were discussed.The results showed that the susceptibility to nitrate dew point corrosion cracking of the weld seam is higher than that of the relevant matrix,the SCC susceptibility of steel 20G is lower than that of steels 16MnR and Q235-A and that the existence of sulphur oxides increases the SCC susceptibility.