PSI - Issue 59

Hryhoriy Nykyforchyn et al. / Procedia Structural Integrity 59 (2024) 125–130 129 Hryhoriy Nykyforchyn, Oleksandr Tsyrulnyk, Oleh Venhryniuk, Olha Zvirko / Structural Integrity Procedia 00 (2019) 000 – 000 5 propagation energy stage is more sensitive for assessing the operational degradation of steels than the crack initiation stage. Table 2. Critical values of the J -integral determined for the 38-year operated 17H1S pipeline steel under different test conditions. Steel state Displacement rate Δ [mm/min] J 0.2 [N/mm] J 0 [N/mm] ( J 0.2 - J 0 )/0.2 [N/mm 2 ] Without pre-treatment 0.5 108 75 165 It has been established that the reduction in the displacement rate of specimens leads to a change in the slope of the J - Δa dependence (Figure 2) towards the Δa axis. For a quantitative assessment of the advantage of the J 0.2 parameter as a fracture toughness measure, a conditional dependency ( J 0.2 - J 0 )/0.2 mm was introduced as the ratio of two legs of the triangle ( J 0.2 - J 0 ) and Δa = 0.2 mm (Table 2). This ratio essentially characterizes the angle of inclination of the J- Δa line to the ordinate axis. A nearly fourfold difference in the value of this parameter was observed when transitioning from the steepest J - Δa line obtained from tests on non -immersed steel at a typical displacement rate to the flattest line obtained from tests on immersed specimens at the lowest displacement rate (165 N and 45 N, respectively). This provides additional evidence for the effectiveness of conducting fracture toughness experiments using the J -integral method at reduced deformation rates to detect the sensitivity of pipe steels to hydrogen embrittlement. 4. Conclusions The J -integral method was adapted to assess the influence of hydrogen pre-charging electrochemically on the fracture toughness of SENB specimens of long-term operated low-alloyed pipe steel, specifically of API 5L X52 strength grade. Under the adopted hydrogen pre-charging conditions, the fracture toughness of the steel, characterized by J 0.2 , decreased by almost half. The reduction in the displacement rate of specimens resulted in a further decrease in the fracture toughness of the steel, nearly halving as the displacement rate decreased by two orders of magnitude. A comparison was made between the standardized J 0.2 fracture toughness parameter and the conditional J 0 parameter at the onset of static crack extension from the top of the fatigue crack, considering their sensitivity to assessing hydrogen embrittlement. The preference was given to the J 0.2 parameter. Acknowledgements The research has been financially supported by the National Research Foundation of Ukraine under the Project No. 2022.01/0099 (grant agreement No 162/0099 on August 01, 2023). References Álvarez, G., Peral, L.B., Rodríguez, C., García, T.E., Belzunce, F.J., 2019. Hydrogen embrittlement of structural steels: Effect of the displacement rate on the fracture toughness of high-pressure hydrogen pre-charged samples. International Journal of Hydrogen Energy 44(29), 15634 – 15643. Andreikiv, O.Y., Hembara, N.Т. , 2022. Modeling of the influence of hydrogen on the deformation of metals. Materials Science 57(6), 774 – 781. ASTM E 813. Standard Test Method for J-Integral Characterization of Fracture Toughness. Boukortt, H., Amara, M., Hadj Meliani, M., Bouledroua, O., Muthanna, B.G.N., Suleiman, R.K. Sorour, A.A., Pluvinage, G., 2018. Hydrogen embrittlement effect on the structural integrity of API 5L X52 steel pipeline. International Journal of Hydrogen Energy 43(42), 19615 – 19624. Briottet, L., Moro, I., Lemoine, P., 2012. Quantifying the hydrogen embrittlement of pipeline steels for safety considerations. International Journal of Hydrogen Energy 37(22), 17616 – 17623. Preliminary hydrogen-charged 0.5 59 38 31 38 26 22 105 0.05 60 45 0.005