Development of the methodology of accelerated testing of oil-gas pipe steels for stress corrosion cracking

Abstract

Tensile stresses present in the pipe steels exposed to corrosive environment can result in the corrosion cracking of the pipe material. The standard procedure used for assessing the susceptibility of steels to stress corrosion cracking (for about 720 h) often does not fully provide insight into the characteristics of the material. The goal of the study is developing of a more rapid test procedure which can provide a reliable and complete information about the material placed in a corrosive environment under stress. Accelerated test for stress corrosion cracking of pipe steels with a relative strain rate of ~10 –6 sec –1 is proposed. The results of testing two materials at different deformation rates placed in different corrosive environments are presented. The tensile diagrams of the specimens tested in air and in corrosive environments containing hydrogen sulfide and carbon dioxide, as well as the measurement of the relative elongation and relative contraction of fractured specimens, were used to determine a degree of the susceptibility of the pipe steels which differ in the strength characteristics to stress corrosion cracking. It is shown that the degree of susceptibility of steel to stress corrosion cracking depends on the characteristics of the corrosive environment and the strength of the pipe steel. Tests under low rate of loading compared to tests with static load of the specimens revealed reduced duration of analysis from 720 – 1000 to 25 – 100 h.