On the choice of equivalent stress for the problem of mechanochemical corrosion of spherical members

This paper compares two models of double-sided mechanochemical wear of thick spherical members subjected to inner and outer pressure. The corrosion rates on the inner and outer surfaces of the sphere are supposed to be linear functions of the corresponding equivalent stress. The possible inhibition of the corrosion process is taken into account. One of the models compared uses the von Mises stress as the equivalent stress while another model uses the maximum principal stress as the equivalent stress. The effect of hydrostatic pressure on the durability of the sphere is investigated. It is shown that, unlike the first model, the second one reflects the effect of hydrostatic pressure. Within the model using the maximum principal stress, the durability may be considerably smaller or larger, depending on the sign of the difference between the inner and outer pressure. It is demonstrated that when the inhibition constant is not equal to zero, the difference between the durability calculated by the use of one model and the durability calculated by the use of another may reach hundreds percent. It is shown that for high-pressure vessels in the conditions of corrosion the maximum principal stress model is more appropriate then the von Mises stress model. Refs 30. Figs 3.