Numerical analysis of hydrogen distributions in the welds of stainless clad steels, which are the structural material of hydrogen storage pressure vessels, was conducted to predict the hydrogen embrittlement in the pressure vessels. The theoretical model for the calculation was based on the activity of hydrogen considering residual stresses induced by welding and hydrogen accumulating sites such as precipitates and dislocations.

From the calculations, hydrogen concentrates at the center of weld metals in both of longitudinal and circumferential directions in welded joints of stainless clad steels. However, the hydrogen contents were much lower than those in the carbide layers, in which are observed in steels with weld overlay of stainless steels, as the calculation of hydrogen distribution in the materials using the higher evaluated diffusion coefficient of hydrogen with considering margin of safety.

Therefore, it seemed that the risk of cold cracking due to hydrogen embrittlement was sufficiently lower in the welds of stainless clad steels during many cycles of shutdown and restart of the pressure vessels in long-term operation.

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