Model of porosity evolution and its practical application for describing the process of hydrogen corrosion during heating (cooling) of a steel cylindrical tube under internal hydrogen pressure

Abstract

The process of nucleation of main cracks in a cylindrical tube deformed by internal pressure of hydrogen has two features, which are determined by the possibility of chemical interaction of hydrogen with steel. In the absence of chemical interaction of hydrogen with the material, under creep conditions, the main crack originates at the outer boundary radius, at which the effective tangential stress reaches the strength ultimate for the first time. During the chemical interaction of diffusing hydrogen with steel, under conditions of high temperature heating, main cracks are generated in the vicinity of the internal boundary radius. To be able to describe these two features, a model of porosity evolution has proposed, in which the relative change in the area of a ring with an infinitesimal thickness have considered as a porosity characteristic. In the mathematical formulation of the problem, all the considered mechanical and physical quantities depend on an arbitrary radius and time, and do not depend on the longitudinal coordinate and angle (the problem with axial symmetry). For the first time in practice, the dependence on an arbitrary radius for large linear displacements has considered, the linearization of which leads to a well known hyperbolic dependence for small linear displacements. Three hypotheses have accepted in solving the problem. The process of formation and growth of micropores does not have a noticeable effect on one of the two boundary radii (in this paper, the external boundary radius is taken as such). The linear size of discontinuities in a material with micropores is taken as the difference between radial displacements in a material with micropores and an incompressible material. The product of porosity and tangential deformation at a point of an arbitrary radius is determined by the product of the corresponding integral characteristics. Taking into account these hypotheses, the dependence of porosity on an arbitrary radius, as well as its effect on radial displacement and strains in a material with micropores, has determined.