PSI - Issue 65

Emelyanov I.G. et al. / Procedia Structural Integrity 65 (2024) 83–91 Emelyanov I.G., Puzyrev P.I. / Structural Integrity Procedia 00 (2024) 000–000

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where 2 H p is the partial pressure of hydrogen in the gas phase, K 0 - dimensionless coefficient, H  - heat of solution, R = 8.314 J·K ¹·mol ¹ - universal gas constant. Values K 0 from 9 to 16, and values H  from 14 to 40 kJ/mol are given in work, Hisamatullin (1990) for some structural steels.

5. An example of solving diffusion problems

As an example of the problem of hydrogen diffusion, work, Emel'yanov, Mironov and Hodak (2019) considered a shell of rotation made of titanium alloy VT20 with a wall thickness h = 0.018 m. During operation, the inner surface of the shell comes into contact with a hydrogen-containing environment. The diffusion coefficient for solving equation (9) for titanium alloys depends on the structure and stability of the phases. After solving the diffusion boundary value problem described by the equation (9) the distribution of hydrogen concentration over the thickness of the shell wall was determined depending on the hydrogenation time. When calculating the structure under study, the boundary conditions on the inner surface of the shell were taken in the form of boundary conditions of the first kind (11). In Fig.3. solid lines show the distribution of hydrogen concentration over the wall thickness, calculated using equation (9). Curves 1-5 correspond to five moments of hydrogenation: 1980, 9972, 19980, 29988, 39996 seconds.

Fig.3. Distribution of hydrogen concentration over the wall thickness for five moments of time in sec.

Thus, during long-term operation of the studied shell structure (more than 11 days), to calculate the stress state it is necessary to use strain diagrams of titanium alloy samples in a fully hydrogenated state. With a shorter operating time, it is necessary to take into account the uneven distribution of hydrogen concentration over the wall thickness, which will also determine the mechanical properties of the material depending on the hydrogen concentration.