Modelling the electrochemical crack size effect on stress corrosion crack growth rate

A model has been developed to predict the crack-tip potential and local chemistry in a stress corrosion crack in a steam turbine blade steel as a function of crack size and bulk chloride-ion concentration. The model incorporates mass transport and chemical and electrochemical reactions in the crack, with the potential drop in the bulk solution outside the crack calculated from the solution to Laplace's equation. The implications for crack-tip electrochemistry of full immersion vs a thin liquid layer are explored. The model predictions provide support for the concept of a solution conductivity dependent crack size effect on crack growth rates.