PSI - Issue 28

Hryhoriy Nykyforchyn et al. / Procedia Structural Integrity 28 (2020) 896–902 H. Nykyforchyn, O. Tsyrulnyk, O. Zvirko, M. Hredil / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 4. Fracture profile of a longitudinal specimen of 30-year operated API 5L X52 steel after the Charpy testing.

5. Conclusions Two main stages are distinguished in degradation of pipeline steels operated at ambient temperature: deformation aging and development of dissipated damaging. On the second stage, the additional substage is recognized for the rolled steels, consisting in a dominant orientation of damages in the rolling direction. These peculiarities, despite in service embrittlement of metal, can lead to a formal increase in certain parameters of plasticity and brittle fracture resistance determined using longitudinal specimens. Hydrogenation of steels intensifies the damaging process due to hydrogen induced microcracking of steel and, in this way, facilitates their operational degradation promoting dissipated damaging, as indicated by hydrogen behaviour studies by extraction and penetration methods. The main mechanism of microdamaging for textured steels is suggested to be the accumulation of hydrogen at the interface “elongated non-metallic inclusion–matrix” creating high pressure in defects with the following microdelamination along the rolling direction. This leads also to anisotropy of characteristics of brittle fracture resistance of rolled steels, which becomes more pronounced with operation time. Hydrogen assisted damaging in pipeline steels during long term operation can lead to formation of macrodelamination, increasing a failure risk. Acknowledgements This research has been partially supported by the NATO in the Science for Peace and Security Programme under the Project G5055. References Andreikiv, O. E., Hembara, O. V., Tsyrul’nyk, О. Т., Nyrkova L. I., 2012. Evaluation of the residual lifetime of a section of a main gas pipeline after long-term operation. Materials Science 48(2), 231–238. Bolzon, G., Rivolta, B., Nykyforchyn, H., Zvirko, O., 2018. Mechanical analysis at different scales of gas pipelines. Engineering Failure Analysis 90, 434–439. Devanathan, V. M. A., Stachurski, Z., 1964. The mechanism of hydrogen evolution on iron in acid solutions by determination of permeation rates. J. Electrochem. Soc. 111, 619–623. Gabetta, G., Nykyforchyn, H., Lunarska, E., Zonta, P. P., Tsyrulnyk, O. T., Nikiforov, K., Hredil, M. I., Petryna, D. Yu., Vuherer T., 2008. In-service degradation of gas trunk pipeline X52 steel. Materials Science 44 (1), 88–99. Gredil, M.I., 2008. Operating degradation of gas-main pipeline steels. Metallofizika i Noveishie Tekhnologii 30, 397–406. Hredil, M., Tsyrulnyk, O., 2010. Inner corrosion as a factor of in-bulk steel degradation of transit gas pipelines, 18th European Conference on Fracture (ECF-18), Dresden, Germany, manuskript #483. Hredil, M.I., 2011. Role of disseminated damages in operational degradation of steels of the main gas conduits. Metallofizika i Noveishie Tekhnologii 33 (Spec. Iss.), 419–426. Hredil, M., Krechkovska, H, Student, O., Kurnat, I., 2019. Fractographic features of long term operated gas pipeline steels fracture under impact loading. Procedia Structural Integrity 21, 153–160. Kharchenko, E. V., Polishchuk, L. K., Zvirko, O. I., 2014. Estimation of the in-service degradation of steel shapes for the boom of a clamp-forming machine. Materials Science 4, 501–507.