PSI - Issue 68

Andriy Syrotyuk et al. / Procedia Structural Integrity 68 (2025) 880–886 Andriy Syrotyuk et al. / Structural Integrity Procedia 00 (2025) 000–000

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we can see an increased interest and intensification of studies dedicated to the impact of hydrogen on the characteristics of ductility, strength, fatigue behaviour, and resistance to fracture of the structural materials for pipeline infrastructure.

Nomenclature W f

energy spent on the specimen fracture [N × m] hydrogen content in material [ppm]

C H

C H(total) total hydrogen content [ppm] C H(dif) diffusible hydrogen content [ppm] C H(res) residual hydrogen content [ppm]

index showing the loss of fracture resistance

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The literature records indisputably indicate that hydrogen demonstrates various effects on the mechanical properties of engineering metallic materials (Barrera et al. (2018)). However, prevail number of investigations in this field have a substantial disadvantage: the true level of hydrogen content in the metal was unknown and this value was taken into account indirectly. Although, the value of hydrogen content in the metal should be considered as the crucial factor (Barrera et al. (2018); Dmytrakh et al. (2015, 2022)). The presented work removes this disadvantage because the study was carried out under the known values of the hydrogen content in the material. Here, in the example of the typical pipeline steel, the effect of hydrogen on its fracture behaviour was studied for the cases of the notch and the crack-like defect in the material. For this aim, the failure tests of the notched and cracked beam specimens with different content of hydrogen C H in the material were carried out and analysed. The bulk content of hydrogen in the metal can be considered as one of the basic parameters that determines the technical state of the pipeline in terms of its further safe operation. In this regard, it is essential to set the ranges of changes in the bulk hydrogen content in the metal C H which differently affect the mechanical properties of pipeline steel, as well as the corresponding critical values C H(critical) at which there is a significant loss of resistance to fracture. The paper considers two cases of in-service damage to the pipeline: the presence of corrosion damage, which is modelled by a notch of a given radius, and a crack-like defect as the extreme case of the stress concentrator in the material. For characterization of the effect of the hydrogen content C H on the fracture behaviour of the pipeline steel, we used the energy W f spent on the fracture of the specimen with a given content of hydrogen in the metal C H . The parameter W f is defined from the diagrams of specimen fracture in the coordinates “load F – displacement Δ” (Fig. 1):

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As a result, the dependencies W f = Φ( C H ) can be constructed on which the corresponding ranges of hydrogen content C H that are safe or dangerous from the point of view of fracture risk in the pipeline, can be found.

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Fig. 1. Schematic view of the diagrams “load F – displacement Δ”.