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in the pipeline element to a critical size at a given hydrogen concentration in the metal,

has been developed based on the obtained calculation and experimental results.

The model combines the results of finite element analysis and the parameters of

the cyclic crack resistance of pipeline steel, which depend on the hydrogen

concentration. A parametric analysis of the influence of internal pressure, crack shape,

and hydrogen concentration on the number of cycles until the crack reaches a critical

size has been performed.

It has been established that the combined action of internal pressure determines

the residual durability of a pipeline, the geometry of a crack-like defect, and hydrogen

concentration in the metal. The period of crack growth to a critical size decreases by

approximately 6–8 times as the internal pressure increases from 8 to 20 MPa. A change

of the crack shape parameter a/c (the ratio of the ellipse semi axes) can reduce the

residual durability of a defective pipeline by up to 3 times. The residual durability

decreases by approximately 85–95% in comparison to the initial level at a hydrogen

concentration of 5–6 ppm in the pipe metal.

The scientific novelty of the results lies in the development of a computational-

experimental approach to assess the residual durability of pipelines with internal semi-
elliptical cracks, for the first time taking into account the hydrogen concentration in the

metal, internal pressure, and defect geometry. A new mathematical model, which
combines the determination of the distribution of diffusible, trapped, and total

hydrogen in pipeline steel, taking into account the stress-strain state and hydrogen
trapping according to the well-known Oriani model, has been proposed. Quantitative

patterns of the influence of hydrogen concentration on the parameters of pipe steel

cyclic crack resistance and pipeline residual durability have been established.

Modeling of the stress-strain state of a pipeline element with an internal semi-elliptical

crack has been improved by taking into account the relationships among local stresses,

plastic deformation, and hydrogen concentration in the metal.

The practical significance of the dissertation’s results lies in the creation of a

computational and experimental model that allows quantitative assessment of the

residual durability of a pipeline with a crack-like defect in a hydrogen-containing