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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It should be noted that the parameter W f is indicative and conditional. It is used only to establish the characteristic ranges of change in hydrogen content, which correspond to significant changes in the fracture behaviour of the pipeline steel. The value of W f is easy to determine, but W f should not be considered as a special invariant characteristic of the material which is opposed to K c or J c , for example. We tried to establish the characteristic ranges of the hydrogen content in the pipeline steel, that correspond to different features of hydrogen effects on the fracture mechanisms, as well as to determine the value of critical hydrogen content which significantly reduces the strength properties. Thus, on the diagram W f = Φ( C H ), the most important is the X-axis and the Y-axis plays the secondary role. Below, based on the results of special experimental studies, the diagrams W f = Φ( C H ) for pipeline steel in the presence of a notch and crack-like defect in the material are constructed. They were analysed together with the data of scanning electron microscopy and the results of the determination of the diffusible and residual hydrogen contents in the tested specimens. 2. Details of the experimental study For the present study, the typical ferrite-pearlite pipeline steel with nominal chemical composition (in weight %): C = 0.17–0.24; Si = 0.17–0.37; Mn = 0.35–0.65; S < 0.04; remainder Fe, was chosen. The two types of beam specimens were used (Fig. 2), namely: with the notch of a given radius which is the model of corrosion damage and with the crack-like defect. Before testing the specimens were preliminary hydrogen charged to the different values of hydrogen content C H within the range C H @ 0.01–2.00 ppm. For this purpose, they were saturated in gaseous hydrogen in a special chamber at the pressure of 5.5 MPa and a temperature of 400 °C (Fig. 3).

Fig. 2. Beam specimens with notch (a) and crack (b).

Fig. 3. Special chamber for hydrogen charging of specimens.

For the determination of the hydrogen content in the specimens, the hydrogen analyser LECO DH603 was used which provides a fast and accurate measurement of the values C H (Bolzon et al. (2021)). We determined the total hydrogen content C H(total) as well as the content of diffusible hydrogen C H(dif) and the content of residual hydrogen C H(res) , suggesting that:

(2)

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Here, the special procedure was applied which is described in our recent work (Dmytrakh et al. (2024)). Received trends in changing the residual C H(res) and diffusible C H(dif) hydrogen content in the specimens were used for the analysis of the dependencies W f = Φ( C H ). Each specimen was tested for failure under increasing static load according to the scheme of three-point bending. During the tests, the diagrams “load F – displacement (deflection) Δ” were recorded. The fracture surfaces of the specimens were examined using a scanning electron microscope EVO-40XVP. Received experimental data served for the construction of the dependencies W f = Φ( C H ) and also for their analysis. 3. Result and discussion Based on received experimental diagrams “load F – displacement Δ” and using the formula (1), the corresponding values of the parameter W f as the function of the total hydrogen content C H(total) in the specimens were calculated (Fig. 4). Hereinafter