The study on stress corrosion behavior of X65 steel welded joint in marine environment

摘要

Pipeline is important equipment for deep sea oil and gas development. More than 138 strip pipeline are laid in deep sea water, the total length of submarine pipeline is more than 4000km. According to the United States MMS ( Minerals Management Service ) statistics, total of 690 failure cases happened in sea bottom in Mexico during 1967 to 1987, average more than 35 accidents happened every year. For date, at home and abroad, the law and characteristics of corrosion of pipeline are mastered in shallow sea after many years practice; but the study on corrosion behavior of pipeline in deep sea environment is quite deficient. Hence, the studies of material corrosion in deep sea attract people's much attention. It is well known that the deep sea environment is not only characterized by high hydrostatic pressure (it increases 1atm for each 10 m in depth), but also low oxygen and temperature. In this environment, the uniformity corrosion of pipeline is inhibited and the effect of hydrogen permeation is enhanced. Then, all these can cause localized corrosion more likely.from which SCC can be easily initiated. Meanwhile, the welded joint is the most sensitive partsto corrosion.In some condition, the welded joint corrosion often evolve into SCC with the corrosion process, it can cause serious damage.