Effect of loading technique on stress corrosion cracking in compact tension specimens exposed in light water reactor environments

The simplest, and often the cheapest, way of achieving crack growth rate data, for instance for disposition lines, are bolt loaded specimens. Bolt loaded specimens can be exposed to simulated reactor water in laboratory loops, or to reactor water in test systems in commercially operating nuclear power plants. This type of loading is passive and one disadvantage is that the load, and consequently the stress intensity factor, is unknown once the specimen is loaded and will change due to load relaxation and crack growth. Therefore, the most common way in laboratory testing is to load specimens under either constant load or constant stress intensity factor conditions in combination with a sophisticated crack growth monitoring technique of sufficient resolution. This is an active type of loading because the load on the specimen is controlled (and measured), and it can be adjusted to the desired value. This paper compares and discusses different loading techniques and their effect on stress corrosion crack growth rates and fracture surface morphology. Compact tension specimens of Alloy 182 have been tested at constant load, constant stress intensity factor and constant displacement in BWR environments. (author)