Sulfide Corrosion Cracking of Linepipe for Sour Gas Service Available to Purchase

Sulfide corrosion cracking of linepipe steel was studied from metallurgical and environmental standpoints using laboratory and full size tests. Sulfide corrosion cracking can be classified into hydrogen induced cracking (HIC) and sulfide stress cracking (SSC). HIC initiates at an elongated inclusion and tends to propagate along microstructural inhomogeneity. The addition of copper was effective in preventing HIC in a relatively mild BP solution, due to the formation of a protective film, but was ineffective in a NACE solution. Calcium treatment of desulfurized steel was effective in preventing HIC initiation. Optimization of the manganese content for controlled rolled plate, and the quenching and tempering process were effective in controlling HIC propagation in a NACE solution. SSC in linepipe steel was closely related with HIC. Measures for HIC were also effective in increasing SSC resistance. Girth welded joints were the most susceptible since SSC occurred at the hardest point in the heat affected zone of the final welding pass. Critical hardness for SSC under the stress level of 1.3 times the yield deflection was Hv 250 and 280 for 1.0 and 0.1 atm partial pressure of H₂S gas, respectively. In a full size HIC test simulating an actual pipeline, HIC developed only in the inner side of the steel, resulting in a decrease of the average crack length by one half as compared with laboratory test results. The residual tensile stress of 50 kg/mm² due to girth welding did not introduce any SSC by itself.