COLD WORK EFFECTS ON SULFIDE STRESS CRACKING OF PIPELINE STEEL EXPOSED TO SOUR ENVIRONMENTS

Cold work effects on sulfide stress cracking of a pipeline steel were examined for exposure to a sour gas environment. Cold worked steel was found to be sensitive to hydrogen embrittlement. The fracture toughness decreases with increasing cold work. Sufficiently low values of fracture toughness may be achieved to promote plane strain fracture even in relatively thin laboratory specimens after a steady state level of hydrogen has occurred in the material. Sulfide stress cracking failure of steel with low amounts of cold work (<30%) is by transgranular cleavage fracture, while heavily cold worked steel shows secondary cracks and microvoid coalescence. The results indicate that sulfide stress cracking of the steel is a mixture of anodic stress corrosion cracking (SCC) and hydrogen embrittlement. The anodic SCC mechanism is mainly promoted by carbon dioxide and a high level of chloride.