Experiments have been performed which determined the growth rate of short cracks (initial depth ~ 0.1 mm) for five high-strength steels (yield stress 370–570 MPa) in air and natural seawater. Attention was focused on regions I and II of the classical da/dN-ΔK curve with test conditions being relevant to offshore structure service. The results indicated enhanced growth rate for short fatigue cracks (a ⪝ 1 mm) in both environments. Parameters with which short crack fatigue behavior might best be correlated were investigated, and it was found that the enhanced fatigue crack growth rate associated with short cracks transitioned to long crack growth kinetics at a ΔK value which depended only upon environment. The significance of the results are discussed within the context of offshore structure integrity.

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