The need for higher strength Sulfide Stress Cracking (SSC) resistant steels is increasing with the increasing development of High Pressure/High Temperature (HPHT) oil and gas fields. This has lead to a requirement for higher strength steel casing materials that also have suitable sulfide stress cracking (SSC) resistance for the mildly sour environments often encountered, or that can occur as a result of reservoir souring (e.g. as a result of sea-water flooding). A 125ksi (862MPa) grade high strength low alloy (HSLA) steel OCTG for mildly sour applications was investigated from the viewpoint of reducing dislocation density and controlling carbide morphology to enhance the SSC resistance. Vanadium containing steels, 1Cr-0.7Mo-0.1V and 0.5Cr-0.7Mo-0.1V revealed lower dislocation densities (half width values) than vanadium-free steels, 1Cr-0.7Mo and 0.5Cr-0.7Mo at same strength levels, because vanadium containing steels were tempered at a higher temperature than vanadium-free steels. The higher temperature tempering enhanced SSC resistance, as a result of the uniform and spheroidized M3C distribution and decrease in dislocation density. The decrease in Cr content, which had little effect on temper softening resistance, was beneficial for preventing M23C6 (M=Fe, Cr, Mo) formation. The 0.5Cr-0.7Mo-0.1V steel without M23C6 carbide had higher SSC resistance than the 1Cr-0.7Mo-0.1V steel. As a result, a 125ksi grade HSLA steel OCTG with vanadium addition and low Cr (0.5%Cr, 0.7%Mo and 0.1%V) has been developed for mildly sour environments.

Subject
Materials, Piping, Carbides, Dislocation, Sour environments, Vanadium, Density, Cracking resistance, Chemical composition, Steel, Sulfide stress cracking, Alloys, Tempering
Keywords:
OCTG, Casing, Carbide, Sulfide stress cracking, High strength low alloy steel, Mildly sour environments
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2005
Association for Materials Protection and Performance (AMPP)
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