PSI - Issue 36

V. Zapukhlyak et al. / Procedia Structural Integrity 36 (2022) 378–385 V. Zapukhlyak, Yu. Melnychenko , І . Оkipnyi et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 1. Hydrogen distribution on the pipe wall thickness at different time periods of hydrogenation 1 – τ= 0.01 ; 2 – τ= 0.05 ; 3 – τ= 0.1 Under boundary conditions, when the whole absorbed hydrogen is in the metal wall, experimentally measured hydrogen distribution in the wall is determined by the equation ( ) ( )  − − =   e s e , , С C C X C X C   ( )   ( ) ( ) ( )   ( )     ( )  + − +  + −   + − −    = 1 2 2 2 2 sin exp cos 1 2 1 ch ch 1 n n n n т n т X X              . (3) Analyzing the kinetics of hydrogen saturation both under total hydrogen desorption block from metal conditions as well as under its total desorption from metal conditions, we can argue, that at low values of non-dimensional time τ , the saturation intensity is practically the same. As can be seen from the above-mentioned material, there is a danger of pipe steel hydrogen acquisition during some repairs using welding even without any additional hydrogen concentration in the pipeline, resulting in mechanical properties change, namely in the making pipe metal brittle in the welded joint area. Therefore, one must take into account the technical state of the gas pipelines line pipe while choosing them for their further use under gas-hydrogen mixture transportation conditions so that to provide their reliability. Due to the above-mentioned reasons, one should choose the pipelines of higher parameters of reliability for gas-hydrogen mixture transportation which will not need any repair shortly. As the pipeline repair under pressure conditions will be almost impossible, and the pipeline liberation of gas during the repair will cause heavy economic expenditures. The choice of separate GTS objects or sections for their further use in the system of gas-hydrogen mixture transportation must have a scientific foundation. Therefore, it is necessary to develop a mathematical model for the determination and forecast of the specified object or a line pipe technical position based on the diagnostic examination, mechanical tests, and stochastic study. As a result, it’s necessary to obtain the parameter of comparison of separate single -purpose technological objects according to which the objects are divided into two categories: those which should be taken out of service due to their failures and the more reliable ones for further use (Yavorskyi et al., (2017), Zhang et al., (2018), Kryzhanivskyy et al., (2019)). 3. Results of determination of gas pipelines design reliability and their discussion. It is well-known, that nothing but the design reliability characteristics are taken into account under the gas pipeline taken out of service for capital repair conditions, whereas the environment (mainly soil) as an impact factor on the corrosion processes in the pipe wall is neglected. Nevertheless, in the case when the gas pipeline is going to be taken out of service, one should take into consideration not only the design reliability characteristics but their forecasted parameters based on retrospective analysis and the results of the pipe wall and insulation actual state diagnostics as well (to detect any defects), and also the results of environmental impact forecast.        