Sulfide Stress Corrosion of Some Medium and Low Alloy Steels

Abstract

Abstract A study made of factors influencing sulfide-stress corrosion of a number of low alloy and medium alloy steels showed that their delayed failures when exposed simultaneously to stress and the corrosive action of acidified brine-hydrogen sulfide solutions have most of the features of hydrogen induced, delayed brittle failures. Different steels subjected to the same exposure conditions showed varying degrees of embrittlement as measured by ductility loss in bend tests. Ductility could be restored partially by room temperature storage. Ductility restoration was related to the amount of hydrogen removed after exposure. Delayed failure under stress occurs when corrosion generated hydrogen is absorbed, and lowers fracture strain until it equals the strain under load. A minimum applied stress was obtained for each steel below which failure did not occur. This “threshold” stress decreased as strength level increased and depended simultaneously on composition and microstructure. Nickel had little effect on cracking behavior of a steel whereas carbon appeared to be detrimental. Twinned martensite was more susceptible than untwinned martensite. Steels containing austenite were more resistant than body-centered steels.