2009 W.R. Whitney Award Lecture: Local Hydrogen Generation and Its Impact on Environment-Assisted Cracking and Crevice Corrosion

An overview is given of the key role for reduction of hydrogen ions and water in determining the local chemistry and electrochemistry in crevices and cracks. Thus, the ability to cathodically protect long, tight crevices and cracks is explained on the basis of depletion of oxygen but also on the slower kinetics for hydrogen generation consequent upon the locally elevated pH. The conditions for developing locally acidic conditions in cracks are described and used to rationalize the “chemical short crack effect” in corrosion fatigue. It is then shown how the relative magnitude of the kinetics of hydrogen generation at the crack tip and on the surface external to the crack need to be considered in testing for resistance to hydrogen-assisted cracking. The importance of internal reactions in the context of boiling water reactor crack chemistry is highlighted, and finally, ideas about constraining crevice attack by increasing the local hydrogen evolution kinetics are explored.