Evaluation of potential ranges for susceptibility to SCC by electrochemical measurements, constant strain rate and constant load stress corrosion cracking experiments

Abstract

AbstractFor the prediction of possible failures due to SCC as well as for corrosion prevention by anodic or cathodic protection, the evaluation of critical potential ranges for susceptibility to SCC is of great practical importance. For this purpose, accelerated testing techniques have been described in the literature basing on the conception that critical potential ranges for SCC are characterized by marked differences of the slope of the stationary and nonstationary measured current‐potential‐curves.The validity of this conception was investigated for two systems: (i) 18/8 stainless steel/boiling 42% MgCl2 and (ii) low‐alloy C‐Mn‐steel/3M Na2CO3 (40 to 70 °C). Experimental data were obtained by (i) potentiodynamically with high and low potential sweep rates measured current‐potential‐curves; (ii) constant‐load and (iii) constant strain rate SCC experiments. The SCC experiments were run under potentiostatic control and followed by careful metallografic investigation of the specimens.From the experimental results one has to conclude that differences in the slope of the current‐potential‐curves measured with variable, high and low potential sweep rates, are no necessary precondition for the occurence of SCC. Possibly they can give indication for experimental conditions under which SCC might be expected, but they are no substitute for conventional test methods to investigate susceptibility of materials to SCC.