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stresses and equivalent plastic deformation in the vicinity of the crack contour are

determined in the elastic-plastic formulation. It is shown that the most dangerous zone

is formed along the crack contour, and the maximum of hydrostatic stresses occurs at

a certain distance from the contour, which is associated with the redistribution of

stresses in the plastically deformed zone. It is established that the maximum values of

hydrostatic stresses and plastic deformations increase with increasing internal pressure,

and the crack geometry (the ratio of the ellipse semi-axes) significantly affects the

nature of the localization of these parameters. A mathematical model for estimating the

hydrogen concentration in pipeline steel under hydrogen-charging conditions, in which

the total hydrogen concentration is given as the sum of the diffusible and trapped

components, has been developed. The flow of diffusible hydrogen is described, taking

into account the influence of hydrostatic stresses, and hydrogen trapping is described

based on the well-known Oriani model, accounting for the relationship between trap

density and equivalent plastic deformation. As a result, it was established that a non-

uniform distribution of hydrogen with a local maximum near the defect is formed in

the region at the front of the semi-elliptical crack contour. It was shown that at high

internal pressure, the contribution of trapped hydrogen to the total concentration
increases significantly, which increases the risk of the growth of the hydrogen

embrittlement level of the pipeline metal, and therefore the risk of accelerating the
growth of the existing crack-like defect.

The patterns of the influence of hydrogen concentration in the metal on the
characteristics of cyclic crack resistance in pipe steel were experimentally established.

It was shown that with an increase in the hydrogen concentration in the metal, the

resistance of the steel to the fatigue crack development significantly decreases, the

threshold and critical values of the stress intensity factor range decrease, and the crack

growth diagrams become steeper, indicating the acceleration of the crack-like defect

development under cyclic (pulsating) loads.

A model for predicting the residual durability of a pipeline with an internal semi-

elliptical crack, which determines the growth period of the existing crack-like defect