Crack growth rate measurements on Alloy 600 steam generator tubing in primary and hydrogenated AVT water

Despite the numerous studies dedicated to assess the intergranular stress corrosion cracking (IG-SCC) behavior of alloy 600 in high temperature water, few reliable crack growth rate data exist. It is often difficult to obtain a consistent picture of the cracking kinetics of this alloy because of the disparity of the techniques and the scatter in the experimental conditions used. Preliminary results of longitudinal crack growth rate measurements on a new tubular fracture mechanics specimen have been previously presented. The influence of cold work and hydrogen partial pressure were partially assessed. Further work is presented in this paper on longitudinal crack growth rate measurements on steam generator tubing in primary water and AVT using a direct current potential drop technique on the same tubular specimens. This study has been focused on the influence of temperature between 315 and 360 degrees C, loading (stress intensity factor) and cold work on the crack growth rate of alloy 600 in primary water. Activation energies between 80 and 160 kJ/mol have been found depending on the loading conditions. The increased susceptibility with cold work has been confirmed. In the nominal secondary AVT water at 360 degrees C, IG-SCC has only been observed when adding hydrogen. The influence of hydrogen partial pressure has been studied between 0 and 0.3 MPa. In this environment, crack growth rates were comparable to those found in primary water