Abstract
The fatigue crack growth rates in an X65 line pipe steel in crude oil environment with two different contents of H2S, ~1 ppm and saturation (~4700 ppm) were measured at three low cyclic frequencies. The maximum acceleration of growth rate relative to that in air was 3 times at the low H2S content and 20 times at saturation level. The results are compared with fatigue growth rates in a 3.5% NaCl aqueous solution at cathodic and free corrosion potentials. Fractographic examination revealed identical brittle striations in both environments when a substantial growth acceleration occurred, indicating hydrogen embrittlement. A complex effect of the stress intensity range, frequency, and hydrogen charging ability of the environment on the fatigue crack growth rate is shown.

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