The effect of acetic acid on the stress corrosion cracking of 3.5NiCrMoV turbine steels in high temperature water

The effects of acetic acid on the stress corrosion cracking (SCC) susceptibility of ASTM A470/471 turbine disk/rotor steels (3.5NiCrMoV) were evaluated. Thus, this study investigated the possibility of corrosion damage to turbine components due to acidified, early condensates containing acetic acid, which is a common impurity in steam cycle systems. Constant extension rate tests (CERTs) were carried out in aqueous solutions containing acetic acid at various concentrations (pH 3–5) at 150 °C to ascertain the susceptibility in terms of strain to failure and reduction in area upon fracture. Acetic acid significantly affects the SCC susceptibility of the turbine steels with the susceptibility increasing with increasing acetic acid concentration, except at the very highest concentration at which excessive dissolution led to crack blunting. The SCC susceptibility test results were analyzed using the CEFM (Coupled Environment Fracture Model), and it is shown that this model accounts for the experimentally–observed relationships between the SCC growth rate and the concentration of the acetic acid in terms of the conductivity of the solution.