PSI - Issue 59

Oksana Hembara et al. / Procedia Structural Integrity 59 (2024) 190–197 Oksana Hembara et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Substituting the values of V H , R and T , we finally obtained the relationship to determine the concentration of diffusive hydrogen as a function of hydrostatic stress in the vicinity of the crack-like defect:   4 ln 8.21 10 L B h C C const      (12) where σ h is measured in MPa. This relationship was obtained from equation (2) by neglecting the prior plastic deformation. 4. Results and discussions First, we determined deformations and stresses by solving the elastic problem. Fig. 2 illustrates the distribution of hydrostatic stresses around crack-like defects under an internal pressure of 7 MPa. a b

Fig. 2. Distribution of hydrostatic stresses around crack-like defects under an internal pressure of 7 MPa: (a) semi-circle crack ( a / c =1); (b) crack ( a / c =0.1).

Next, using the distribution of hydrostatic stresses, we calculated the concentration of diffusive hydrogen according to equation (19). Fig. 3 shows the distributions of hydrostatic stress and the corresponding hydrogen concentration C L along the Ох axis under an internal pressure of 7 MPa. Similar calculations were conducted for higher internal pressures of the hydrogen-containing environment: 10 MPa, 20 MPa, and 30 MPa (Fig. 4). Both distributions of σ h and C L have similar shapes and peaks at a certain distance from the defect surface. According to equation (1) the hydrogen flow is influenced by σ h . Therefore, the distribution of C L is similar to the distribution of σ h for all types of considered crack-like defects. As for the influence of the shape of the crack-like defect on the C L concentration, it increases with the length of the crack relative to its depth at the same internal pressure. Calculations indicate that the maximum value of hydrogen concentration C L is associated with the maximum value of σ h without considering the ratio a / c . a b

Fig. 3. Distribution of hydrostatic stresses (a) and concentration of diffusive hydrogen (b) along the Ox axis from the surface of crack-like defects under an internal pressure of 7 MPa.

We also observe that higher internal pressure leads to higher maximum values of both hydrostatic stresses and the concentration of diffusive hydrogen for all types of investigated defects (Fig. 5). At a pressure of 30 MPa, the maximum value of hydrogen concentration С L is nearly 2 times higher than at 7 MPa. This difference increases as the ratio of crack depth to length a / c decreases.