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Fracture due to hydrogen embrittlement is a major concern for the reliability and safety of hydrogen transportation via gas pipelines. Pipe steels are characterized by high plasticity, therefore, methods of nonlinear fracture mechanics, including the J-integral method, are preferred for determining the fracture toughness. The influence of preliminary electrochemical hydrogen charging under a moderate mode on fracture toughness of API 5L X67 steel in the as-delivered and 34-year operated on the gas main pipeline conditions was studied. A methodological feature of the experiments is the use of different rates of mechanical loading of specimens with cracks. The influence of the long-term operation of steel on its resistance to brittle fracture is revealed, depending on the test conditions. [ABSTRACT FROM AUTHOR]

We analyze the characteristics of in-service degradation of structural steels under the conditions of cyclic loading and take into account that the process of degradation of steels has two stages. In the first stage, cyclic strain hardening is predominant. The second stage can be described as the intense development of microdefects dispersed in the bulk of the metal. We distinguish the influence of in-service cyclic loading on the complex of basic mechanical properties of steels important for their serviceability and on a broad range of the characteristics of fatigue strength. In the first case, these are the characteristics of brittle-fracture resistance and, in particular, impact toughness and crack resistance. In the second case, we deal with fatigue-fracture resistance. The indicated characteristics are determined for smooth specimens and specimens with cracks. We analyze the influence of corrosive hydrogenating media on the intensity of in-service degradation of steels under cyclic loading. [ABSTRACT FROM AUTHOR]

We propose an adaptation of the laboratory express method of degradation of low-alloy steels that combines preliminary electrolytic hydrogenation with subsequent plastic deformation of the specimens and leads to the development, under these conditions, of dissipated bulk damage in the material. The proposed adaptation enables one to predict the susceptibility of gas pipeline steels of different strengths (17G1S, Х60 and Х70) to stress-corrosion cracking in model soil solutions. It is discovered that 17G1S steel is not susceptible to stress corrosion cracking in the as-received state but becomes susceptible to it as a result of in-laboratory degradation. However, higher strength characteristics of steels do not necessarily lead to a sharper decrease in the resistance to stress corrosion cracking as a result of degradation. [ABSTRACT FROM AUTHOR]