To characterize environmental fatigue crack growth properties of reactor pressure vessel steels, experiments were conducted by a computer-controlled constant alternating stress intensity factor (ΔK) test technique over a wide range of R-ratios and loading frequencies in 288°C water environments. Compact fracture specimens of two nuclear pressure vessel steels were tested over a range of ΔK-values from 16 to 55 MPa √m. Loading frequencies ranged from 0.0017 to 10 Hz, and R-ratios from 0.16 to 0.72.

As many as 22 separate experiments were conducted on a single specimen. The constant ΔK test method permitted crack growth rate measurements to be made with a high degree of confidence over long intervals of crack extension.

A simulated pressurized water reactor (PWR) environment plays only a minor role in the enhancement of fatigue crack growth rates. The applied ΔK was the primary rate-controlling variable, while R-ratio and loading frequency were secondary.

In high-purity deoxygenated water, the environment had a very significant effect on crack growth rates. The loading frequency was a primary rate-controlling variable at low loading frequencies. At high loading frequencies crack growth rates were ΔK-dependent.