Systematic investigation of the role of stress-induced pits and grooves in SSC four-point bend testing of line pipe steel

摘要

The four-point bend test as per NACE TM0316-2016 is used in the oil and gas industry as a common test to evaluate the resistance of line pipe steels to sulfide stress cracking. The appearance of stress-induced pits or grooves on the test specimens can sometimes be noted when testing is performed under high load, at low pH or in CO_2 containing test environments. When evaluating SSC specimens, it is important to distinguish between stress-induced corrosion pits and SSC crack structures and their relevance for the SSC test result. Within this study a systematic investigation of the level of applied stress, the test gas composition and the surface finish of test specimens and their influence on the onset and growth of cracking of four-point bend SSC specimens was performed. In this context the role of shape and maximum depth of stress-induced corrosion pits and stress grooves are discussed in detail.