Page 11 - Дисертаця Венгринюк

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pipeline steels, as well as their variation due to degradation processes. It also

incorporates the calculated stress intensity factors in the vicinity of crack-like defects

in the pipe wall that may remain undetected during technical inspection, taking into

account the geometry of such defects and the hydrogen pressure within the pipeline.

Practical significance of the obtained results

A criterion has been proposed for assessing the serviceability of pipeline steels

under hydrogen transportation conditions, based on the material reaching its limiting

state. The criterion relies on determining the fracture toughness of pre-hydrogenated

specimens under low loading rates and comparing it with the allowable critical value,

while accounting for the presence of potential crack-like defects, service-induced

degradation, applied loading, and hydrogen exposure. The results obtained in this

dissertation have practical relevance for predicting the safe operation of hydrogen

transportation pipelines, both at the design stage of new systems and during the

repurposing of existing gas pipelines.

The established patterns of pipeline steel degradation, characterized by fracture

toughness as a function of hydrogen concentration and mechanical loading rate, the

substantiated criterion for the pipe metal reaching its limiting state during service based
on fracture toughness, and the developed models describing hydrogen diffusion and

predicting the fracture toughness of pipeline steels under hydrogen exposure, have been
utilized by IPP-Center LLC for validating methods of assessing the serviceability of

main gas pipelines and forecasting their reliable and safe operation under hydrogen
transportation conditions.

The scientific findings of this dissertation research – including the established

relationships describing the influence of hydrogen and mechanical loading rate on the

fracture toughness characteristics of pipeline steels, taking into account their current

condition (initial or service-exposed); the mathematical models for predicting the

fracture toughness of pipeline steels as a function of hydrogen concentration and the

degree of service-induced degradation; as well as the substantiated criterion for the

operated steels of main gas pipelines reaching their limiting state in terms of fracture

toughness under hydrogen transportation conditions – have been incorporated in the