Methods for the Evaluation of Corrosion-Hydrogen Degradation of Steels of Oil-and-Gas Pipelines

We analyze the mechanical, structural-fractographic, and electrochemical methods aimed at the evaluation of the in-service degradation of pipe steels with regard for the corrosion-hydrogen influence of aggressive media. Mechanical methods are used primarily for the evaluation of brittle-fracture resistance. However, in the investigation of forge-rolled steels, it is necessary to take into account the possibility of their microdelamination in the axial direction. Preliminary hydrogenation increases the sensitivity of mechanical methods due to the enhancement of the susceptibility of degraded steels to hydrogen-assisted cracking. Among structural factors, we emphasize a special role played by the rolling texture. At the same time, among fractographic factors, we emphasize the role of the fraction of low-energy fractures, such as delamination and intragranular cleavage. The contribution of hydrogenation to the development of steel microdamage is determined by the method of microfractographic analysis. Electrochemical methods enable one to predict the brittle-fracture resistance of steels according to the changes in the polarization resistance and in the fracture surface potential. It is also possible to estimate the degree of dissipated damage and the susceptibility of steels to hydrogen-assisted cracking.