The application of the slow strain rate test method for the development of linepipe steels resistant to sulphide stress cracking

High grade linepipe steels may be sensitive to hydrogen embrittlement in sour environments. This sensitivity may appear under conditions of sulphide stress cracking (SSC) and even in the absence of applied stress. Several metallurgical parameters play a role in this susceptibility. In this study, only SSC is considered. The slow strain rate technique (SSRT) is shown to complement the constant load test method (NACE TM 01–77) in pointing to the influence of some metallurgical parameters and to differentiate more accurately the behaviour of some high grade linepipe steels. The influence of specimen orientation with respect to rolling direction, of rolling conditions and segregation leading to the formation of hard bands on cooling is particularly considered. The influence of experimental conditions on the SSRT results is discussed. The results obtained by these two test methods are in agreement, although SSRT seems more accurate and selective. The choice of sensitivity criteria is discussed and the criterion best describing the material behaviour in the corrosive environment is the normalized uniform elongation. This criterion represents the loss of ductility of the steel due to hydrogen embrittlement.