Rapid straining electrode behavior of iron and nickel base alloys in high temperature and high pressure aqueous solutions

In the rapid straining electrode method, a slight tensile strain is caused quickly in a thin wire to destroy its surface layer, and the initial stage of the electrochemical reaction in the resultant new surface is observed. This technique provides a useful clue to the understanding of the basic corrosion behavior of metal. The present report describes major results of a study on the rapid straining electrode behavior of iron- and nickel-based alloys in high temperature and high pressure neutral aqueous solutions, focusing on the effects of SO42- ions in the solutions and effects of chromium contained in the alloys. The mechanism of the rapid straining electrode method is outlined first. Some study results on the stability of surface layer in aqueous solution containing SO42- ions are then presented, focusing on iron and Fe-Cr alloys, and nickel and Ni-Cr alloys. The process of formation and growth of a surface layer in nickel is briefly outlined. The effect of chromium on the re-passivation of iron- and nickel-based alloys are also described. (N.K.)