Application of the slow strain rate test method to assess the tendency of corrosion-resistant steels and alloys to sulfide cracking

The results obtained after tests using the slow strain rate test method (SSRT) to determine the tendency to sulfide stress cracking (SSC) of corrosion-resistant steels of ferritic, austenitic, austenitic-ferritic and martensitic classes as well as aluminum alloy are considered. The selected materials are used in the oil and gas industry and operated in an acidic aqueous environment when saturated with hydrogen sulfide. The deformation rate at the level of 10 –6 sec –1 is recommended by the NACE TM 0198 standard and was selected during the initial study of these materials (due to low illumination of the SSC results on them) in order to assess the tendency to sulfide stress cracking of corrosion-resistant steels and alloys. In fact, using the promising SSRT method, materials with varying structures are evaluated. The method of stretching with a low deformation rate directly in a corrosive environment has shown its suitability for comparative evaluation of the resistance of steels of various classes to sulfide stress cracking. From the consideration of the tensile curves of the studied materials in a hydrogen sulfide medium, it follows that the destruction of steel samples of grades 08Kh13, 08Kh18N10T, 08Kh22N6T occurs only in the area of plastic deformation, and the destruction of steel samples of grades 17-4PH was noted in the area of elastic deformation on a linear section of the tensile curve. Martensitic class steel 17-4PH showed the greatest sensitivity to the effects of hydrogen sulfide and a threshold stress below the permissible one. Aluminum alloy 1953T1 has not shown a tendency to sulfide cracking (the tensile curves in air and in a hydrogen sulfide medium are almost completely the same) and can be considered as a standard of resistance to this type of corrosion failure. Metallographic analysis of the structure of the studied steels and the nature of the propagation of the formed corrosion cracks allowed us to confirm the influence of the structure, phase composition and strength level of the material on the development of the sulfide stress cracking process.