Mechanistic interpretation on acidic stress-corrosion cracking of NiCrMoV steam turbine steel

Abstract

The present work evaluates the acidic stress-corrosion cracking (SCC) of NiCrMoV steam turbine steel. Between a pH of 4.2 and 7, iron oxidises to Fe2O3, whereas iron dissolution (Fe2+) and hydrogen proton (H+) reduction are favoured at lower pH. The corrosion rate increases with the H+ concentration via a linear relationship as well as by a temperature increase. During in-situ constant extension rate testing, both the ductility and strength losses, caused by anodic dissolution and hydrogen embrittlement, increase with a higher acetic acid concentration. Hydrogen embrittlement causes larger embrittled zones with higher acetic acid concentrations as well as stress-corrosion cracking.