Modeling of the chemistry and electrochemistry in cracks - A review

The state of the art in crack chemistry modeling is assessed. An overview of conceptual understanding of the processes occurring in a crack is given, and the foundations for establishing mathematical equations for the mass conservation of species in a crack are described. With the exception of concentrated solutions, crack chemistry modeling is at the stage where the primary uncertainty in prediction should be associated only with the paucity of data for the input parameters. Establishing an electrochemical database is advocated, The relevance of crack electrochemistry models to predicting crack growth is assessed for low-alloy carbon steel (CS) in seawater sensitized stainless steel (SS) in high-temperature waters, and Ni-P alloy in sulfuric acid (H2SO4). A much clearer understanding of the role of environmental, material, and stress variables has emerged from such modeling, and in some cases prediction of crack-growth kinetics has been made for simple dissolution-based models. However validating specific crack chemistry measurement predictions has been confined to low-alloy steels in seawater, and ongoing research of such measurement is encouraged.