PSI - Issue 42

5

Olha Zvirko et al. / Procedia Structural Integrity 42 (2022) 522–528 Olha Zvirko / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 1. HES indices of the 17H1S pipeline steel in different states depending on the orientation of tensile specimens relative to the rolling direction of the pipe.

According to the data obtained by the tensile testing of the longitudinal specimens no susceptibility of the 17H1S pipeline steel in the as-delivered state and the 20 pipeline steel from straight pipe elbow section to hydrogen embrittlement was revealed: the indices of the specimens are almost zero. At the same time, the hydrogen embrittlement effect on plasticity characteristics determined using transversal and short transversal specimens is significant for both studied steels. As it can be seen from Figs. 1 and 2, the investigated steels showed a pronounced resistance anisotropy to hydrogen embrittlement depending on the plane of fracture propagation relative to the rolling direction of the pipe, and also on degree of its operational degradation. Thus, for the metal of the tensioned section of the pipe elbow the influence of hydrogen on decreasing plasticity is more significant than for the straight one (Fig. 2), especially at testing the short transversal specimens. The similar tendency is inherent to the 17H1S pipeline steel (Fig. 1).

Fig. 2. HES indices of the 20 pipeline steel in different states depending on the orientation of tensile specimens relative to the rolling direction of the pipe elbow.

The higher sensitivity of reduction in area compared with elongation (or relative displacement in the case of usage of notched specimens for tensile testing) to the hydrogen embrittlement can be explained by the dissipated damaging of the operated steel at the nano and microscale. These damages are developed in the rolled pipeline steels mainly in the planes between the fibers of the structure, where there is the weakest cohesion. At the tensile testing of