An Electrochemical Testing Method for Stress Corrosion Cracking by Separating Crack Anode from Cathode

Abstract

The initiation and propagation of stress corrosion cracking (SCC) of austenitic stainless steels in boiling 35% magnesium chloride solution, with the pH adjusted to 3.0, were investigated electrochemically by separating the crack anode from the cathode. The dissolution current accompanying crack propagation can be measured, by connecting the anode with the cathode through an external electric circuit, and as a result, the distinction between crack initiation and propagation becomes very clear. The passive-active cell of SCC, simulated by keeping the crack anode potential at the potential of the cathode using a potentiostat, prevents the coupled potential from falling during crack propagation step, accelerates the dissolution of crack anode, and reduces the time to failure. For materials and environments which have low susceptibility to SCC, it can clearly be determined whether SCC occurs or not, by comparing the critical potential for crack propagation, not for initiation, with the corrosion potential of the unstressed steel in the environment concerned. If the former is more active than the latter, SCC can occur. The present method was applied to predict SCC in some chemical equipment, and successful results were obtained.

Effects of applied potential on stable pitting of 304 stainless steel

“…Although the electrolyte inside the pit has reached saturation, the pH does not reach the theoretical minimum, since it is depended mainly on the magnitude of ih. Some researchers report that the pH in the pit electrolyte can be as low as zero, and the concentration of metal chlorides can be as high as 12 M. These studies may have been conducted at a higher temperature and had a larger ih [50][51][52][53].…”

A Combined Experimental and Computational Approach to Study Crevice Corrosion of Stainless Steels

“…In-situ measurement of some crevice parameters (pH, potential, and chloride concentration), [32][33][34][35] corrosion damage, 36 or using more advanced technologies such as capillary glass tubes and acoustic emission [37][38][39] have shown to be promising developments but still require high precision instruments to be implemented. Electrochemical techniques using a three-electrode set-up working at rest potential have, however, proven to be suitable for real-time monitoring of crevice corrosion kinetics.…”