Corrosion fatigue in pressure vessel steels for light water reactors

Abstract

One of the factors of importance to the safety in service of large pressure vessels for water-cooled reactors and other conventional high-pressure boiler vessels is the rate of growth of any small defects remaining after fabrication. It is now known that the aqueous environment within such vessels, typically at 280–350°C and 7–17 MPa, can cause fatigue cracks in pressure vessel steels to grow considerably faster than they would in air at the same temperature, despite the fact that these steels are not susceptible to constant stress corrosion cracking under any permissible water chemistry or operating conditions. The degree of the water effect on fatigue crack growth is very sensitive to the stress cycle frequency in the range 1.0–0.001 Hz, the stress ratio R between 0.1 and 0.7, and the water temperature. The published data are reviewed and any possible conclusions regarding the nature of the mechanisms operating are highlighted.