Effect of nonmetallic inclusions on hydrogen delamination of low-alloy steels

Because of the development of new deposits of oil and gas, including in the shelf zone, increasing attention is being paid to the performance of low-alloy steels in hydrogen-sulfide containing media. The presence in the product of even a small amount of hydrogen sulfide (to 5 vol.%) has a catalytic effect on the hydrogen charging of low-alloy steels [i ,2] and, consequently, on their embrittlement and corrosion cracking. In addition to hydrogen sulfide cracking, the greatest risk for low-alloy structural steels with the tensile strength of up to 700 MPa and a hardness of up to 240 HB in operation in these conditions is presented by internal hydrogen cracking, i.e., the formation of delaminations and planes in the metal as a result of hydrogen charging [3]. This type of failure is associated directly with the structural characteristics, including the nature, form, and distribution of nonmetallic inclusions, especially the sulfide phase. Therefore, comprehensive examination of the interaction between the hydrogen diffusing into the steel and the nonmetallic inclusions is of considerably theoretical and applied value, especially in developing steels for equipment used in extracting and processing hydrogen sulfide-bearing oil and gas.