The mechanism of hydrogen-facilitated anodic-dissolution-type stress corrosion cracking: theories and experiments

A novel concept of hydrogen-facilitated dissolution has been introduced to describe stress corrosion cracking (SCC) in metals under hydrogen, stress a nd dislocation effect. Related experiments for pipeline steels in dilute bi carbonate solution were conducted to support the proposed mechanism. slow-s train-rate tests (SSRTs) indicate that pre-charged hydrogen plays an import ant role in SCC by promoting anodic dissolution and SCC susceptibility. The hydrogen evolution and enrichment around a stress corrosion crack tip were identified using secondary-ion mas spectroscopy and its distribution aroun d a SCC crack was modelled using an elastic-plastic analysis. It is postula ted that the presence of hydrogen plus stress makes the anodic dissolution reaction more thermodynamically favourable. A thermodynamic model is propos ed which is used to calculate the effect on the SCC growth the presence of hydrogen and stress. The results obtained with the model are in agreement w ith SSRT measurements.