Formation of bubbles by hydrogen attack and elastic–plastic deformation of the matrix

Abstract

Steel pipes used in oil industry are subjected to environmental conditions, which may provoke generation of atomic hydrogen at their surface by electro-chemical processes. A part of the atomic hydrogen recombines to molecules and the remaining part enters the bulk of the pipe and causes the well known hydrogen attack with several negative effects. One of them is the formation and growth of bubbles. Hydrogen atoms diffuse in steel to the surface of the bubbles, they recombine there to gas molecules and increase the gas pressure in the bubbles. The pressure may then reach a value sufficient for the growth of the bubbles by elastic or elastic–plastic deformation of the matrix.The problem of kinetics of bubble formation and growth nucleated at an inclusion is treated by a thermodynamic model combining diffusion of hydrogen from the system surface to the bubble surface with the growth of the bubble by elastic or elastic–plastic deformation of the matrix. The processes are driven by the release of the Helmholtz free energy of hydrogen. The according driving force is spent for dissipation by diffusion, for elastic or elastic–plastic deformation of the matrix and for the increase of the bubble surface energy. The model is demonstrated on several simulations of bubble growth kinetics in iron and copper.