Monitoring behaviour of 304 stainless steel under constant tensile loading by electrochemical impedance spectroscopy

This paper presents the potential use of electrochemical impedance spectroscopy (EIS) for the electrochemical study of stainless steel behaviour under different constant loads and for the detection and characterisation of stress corrosion cracking (SCC). The test specimens were made from sensitised stainless steel of type 304 and were immersed in 0.5M aqueous solution of sodium thiosulphate. The specimens were subjected to constant load tests. Different load levels were applied in order to provoke and evaluate different experimental conditions. The results of EIS measurements clearly showed that the initial polarisation resistance is inversely proportional to the increasing load level. The polarisation resistance also changes with time. Although EIS is generally used for the characterisation of stationary processes, basic electrochemical parameters indicated temporal breaks of the passive film. It was confirmed that under stress, these damages can initiate SCC. It can therefore be concluded that EIS can be used as a supplementary technique for monitoring the initial phases of intergranular SCC.