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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Based on the received data, the special diagram in the coordinates “ – ” was constructed (Fig. 7). This diagram consists of three zones marked as green, yellow, and pink colour (see Fig. 7). The green zone refers to the conditional plasticization of steel due to the action of the low content of diffusible hydrogen, which causes the increase in defectiveness of materials microstructure. This zone is denoted as the zone of enhanced deformability (ED). The yellow zone is the transition zone, where two mechanisms of the hydrogen effect are realized, namely: the enhanced deformability and the hydrogen embrittlement (ED + HE). The pink zone is the zone where hydrogen embrittlement (HE) dominates. Here it can be noted as follows. The fact of coincidence of three characteristic ranges of the hydrogen content for two independent series of tests (notched and pre-cracked specimens) can serve as evidence that the received results are invariant. Hence, three different mechanisms of hydrogen influence on the fracture behaviour are inherent for given pipeline steel. The diagram is the basis for determining the critical content of hydrogen C H(critical) in the metal. Here, the parameter C H(critical) defines the hydrogen content in the metal, which significantly reduces the resistance of the material to fracture. The analysis of the obtained data showed that the values of the critical hydrogen content for the considered steel are within the range C H(critical) @ 0.6–1.0 ppm (see red zone in Fig. 7). The parameter C H(critical) can be recommended as a baseline for assessing the potential risk of failure of defected sections of pipelines for the transportation of hydrogen-containing agents. 4. Conclusions The effect of hydrogen in pipeline steel on its fracture behaviour has been evaluated based on the failure tests of the notched and cracked beam specimens with different contents of hydrogen C H in the material. Here, the total energy W f spent on the fracture of the specimens was used as the conditional indicator and corresponding dependencies W f = Φ( C H ) were constructed. Three characteristic ranges of the hydrogen content that correspond to different features of the hydrogen influence on the microstructural fracture specificity of pipeline steel have been found, namely: the zone of enhanced deformability of material, the transition zone with the mixed mechanism of hydrogen effect, and the zone of hydrogen embrittlement. The specificity of these zones can be explained by the consideration of the ratio between the diffusible C H(dif) and residual hydrogen C H(res) in the total amount of C H(total) in the steel, and the SEM examination of the fracture surfaces confirmed this relationship. Based on the received results, a special index showing the loss of the fracture resistance of the steel depending on the hydrogen concentration C H in the steel was proposed. The parameter may be used as criteria for the evaluation of the in-service reliability of the defective pipelines. References Barrera, O., Bombac, D., Chen, Y., Daff, T. D., Galindo-Nava, E., Gong, P., Haley, D., Horton, R., Katzarov, I., Kermode, J. R., Liverani, C., Stopher, M., Sweeney, F., 2018. Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum. Journal of Materials Science 53 (9), 6251–6290. Bolzon, G., Gabetta, G., Nykyforchyn H., Eds., 2021. Degradation assessment and failure prevention of pipeline systems, in “Lecture Notes in Civil Engineering”, vol. 102 . Springer International Publishing, pp. 252. Djukic, M., Sijacki Zeravcic, V., Bakic, G., Sedmak, A., Rajicic, B., 2015. Hydrogen damage of steels: A case study and hydrogen embrittlement model. Engineering Failure Analysis, 58, 485–498. Dmytrakh, I., Leshchak, R., Syrotyuk, A., 2015. Effect of hydrogen concentration on strain behaviour of pipeline steel. International Journal of Hydrogen Energy 40, 4011–4018. Dmytrakh, I., Syrotyuk A., Leshchak R., 2024. Special diagram for hydrogen effect evaluation on mechanical characterizations of pipeline steel. Journal of Materials Engineering and Performance 33 (7), 3441–3454. Dmytrakh, I., Syrotyuk, A., Leshchak, R., 2022. Specific mechanism of hydrogen influence on deformability and fracture of low-alloyed pipeline steel. Procedia Structural Integrity 36, 298–305. Lynch, S. P., 2003. Mechanisms of hydrogen assisted cracking – A review, in “Hydrogen Effects on Material Behaviour and Corrosion Deformation Interactions”. In: R. H. J. N. R. Moody, A. W. Thompson, R. E. Ricker, G. W. Was (Ed.), pp. 449–466. Mulder, G., Hetland, J., Lenaers, G., 2007. Towards a sustainable hydrogen economy: Hydrogen pathways and infrastructure. International Journal of Hydrogen Energy, 32 (10–11), 1324–1331. Wasim, M., Djukic, M., Ngo, T., 2021. Influence of hydrogen-enhanced plasticity and decohesion mechanisms of hydrogen embrittlement on the fracture resistance of steel. Engineering Failure Analysis 123, art. no. 105312. ! " # ! ! ! " # ! " # $ = ! ! " # ! " #