PSI - Issue 68

Olha Zvirko et al. / Procedia Structural Integrity 68 (2025) 868–873 Olha Zvirko / Structural Integrity Procedia 00 (2025) 000–000

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It is important to highlight that the impact of hydrogen pre-charging (ex-situ) on the mechanical behavior of steel in air has been studied, specifically looking at the effects of “internal” hydrogen absorbed before testing. These experiments differ from those that examine the combined impact of cathodic hydrogen charging and active loading (in-situ), where the influence of “external” hydrogen is also present.

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Fig. 1. Ultimate strength (a), yield strength (b), reduction in area (c), elongation (d) and impact toughness (e) of the pipeline steel in different states (I – the reserve pipe; II – the operated pipe) depending on the orientation of tensile specimens relative to the rolling direction of the pipe: 1 – longitudinal; 2 – transversal. Figure 2 presents data on the susceptibility of the investigated steels to HE assessed by the indicator НES.

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Fig. 2. HES indices of the pipeline steel in different states depending on the orientation of tensile specimens relative to the rolling direction of the pipe: (a) the reserve pipe and (b) the operated pipe.

The reserved steel is not susceptible to HE under the moderate mode of hydrogen charging ( i = 0.05 mА/сm 2 ) for both specimens’ types (longitudinal and transverse). In general, an API 5L X52 steel in the as-delivered state exhibits low sensitivity to HE (Zvirko et al. (2024)), as confirmed by experimental results. Typically, transverse specimens are more susceptible to HE than longitudinal ones. However, in this study, under moderate hydrogen