N. T. Hembara

The mechanisms of hydrogen-induced failure and the processes of hydrogen transport in metals are considered. A mathematical model of hydrogen diffusion is proposed, which accounts for the interaction between local elastoplastic deformations and hydrogen diffusion. Using the finite element method, the distribution of hydrogen in the vicinity of crack-like defects on the inner surface of steel pipelines under internal pressure is analyzed. Analytical dependences are derived to assess the local hydrogen concentration near defects of various geometric shapes. It is established that with increasing internal pressure, the concentration of both diffusible and trapped hydrogen significantly increases, contributing to hydrogen embrittlement of the material. The obtained results can be used to predict service life of pipelines in hydrogen power applications.

The problem of hydrogen diffusion in a metal with pores is formulated. Pores are sources of absorption (traps) of hydrogen. Traps were considered to be point-like, distributed uni­formly over the entire volume of the metal. Solutions to the problem of diffusion in a defective body have been obtained. In particular, expressions for determining the concen­tration of both diffusion-moving and trapped hydrogen are obtained for the plate. We also obtained a ratio for determining the amount of hydrogen sorbed by a defective plate at an arbitrary moment of time during its hydrogenation. The amount of hydrogen sorbed by a defect-free plate and a plate with uniformly distributed traps was compared. A 2-3 time excess of hydrogen content in the defective plate compared to the defect-free plate was established.

It was established that the metal of long-term operated gas pipelines made of 10G2BT steel contains relatively little hydrogen, which does not create prerequisites for the pipes hydrogen embrittlement. However, for the considered cases, it was established that the microstructure of steel is characterized by increased defectiveness, which increases with the extension of the pipeline operation time. Such a defective microstructure has an increased ability of absorbing hydrogen, and therefore there is a risk of hydrogen embrittlement of the material. It was concluded that the use of long-term operated pipelines for transportation mixtures of natural gas and hydrogen without additional verification is problematic.

On the basis of the previously developed calculation model of hydrogen-induced crack growth in metals under the action of long-term static loading under various HELP, HEDE mechanisms, kinetic diagrams of hydrogen cracking of steels were constructed 4340 and 4147 under different hydrogenation regimes. The residual durability of the plate with a crack under dual hydrogen exposure was calculated.