539 Long-term in-situ study of stress corrosion cracking kinetics in a carbonate-rich solution

A long-term SCC crack growth kinetics study, using precracked WOL samples, was performed. The samples were exposed in a mild steel storage tank containing a solution with high levels of ammonium and carbonate ions. Some samples were fully immersed in the tank content, while in other cases, intermittent drying took place in the tank upper regions. At short times, the highest (intergranular) crack growth rates were obtained at immersed regions and initially, the region with intermittent drying showed considerably slower growth rates. With pronounced exposure times, the trend however reversed and the growth in the intermittent drying region accelerated while the samples in the immersed location experienced a retardation in the SCC growth velocities. It was found that the SCC mechanism progressed through a process where small cracks first formed at the fatigue crack front and thereafter merged to form a continuous SCC crack front.