Page 8 - Дисертаця Венгринюк

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steels is often challenging due to the limited wall thickness of pipes. In this context,

mathematical modelling and machine learning methods provide an effective approach

for predicting the mechanical characteristics of materials while accounting for the

influence of multiple factors. Therefore, the aim of this dissertation is to develop

mathematical models, computational and experimental methods for assessing the

degradation of gas transmission pipeline steels in terms of fracture toughness and to

substantiate a criterion for their limit state under combined loading and hydrogen

exposure.

The object of the study is the fracture processes in pipeline steels under the

action of service loads and hydrogen charging.

The subject of the study is models and methods for assessing the fracture

resistance of transmission gas pipeline steels, taking into account the influence of

mechanical and physico-mechanical factors (loading, hydrogen charging, and

operational degradation of the steel).

The study addresses an important scientific and engineering problem for the

energy sector of Ukraine, namely the development of mathematical models,

computational and experimental methods for assessing the degradation of
transmission gas pipeline steels in terms of fracture toughness under hydrogen

transportation conditions. The obtained results provide a basis for assessing the
serviceability of these steels in hydrogen transport service and for developing criteria

for their safe operation, accounting for material degradation and hydrogen effects.
The sensitivity of the mechanical properties of 17H1S steel from a gas

transmission pipeline in both the as-received and in-service steels was analysed under

tensile testing after hydrogen charging of varying intensity. It was found that 17H1S

steel, which had been in service in a gas transmission pipeline for 38 years, exhibits a

significantly higher susceptibility to hydrogen embrittlement under standard tensile

tests of electrolytically hydrogen-charged specimens compared to the as-received

steel. In contrast, the as-received steel shows sensitivity to hydrogen only when

specimens are oriented transverse to the pipe axis and subjected to high-intensity

hydrogen charging.