Environmental Influences on the Aqueous Fatigue Crack Growth Rates of HY-130 Steel

Abstract

The influence of chloride ions, pH, potential, and chromate ions on fatigue crack growth rates of HY-130 steel in aqueous solutions were examined. Crack growth rates (da/dN) were determined as functions of stress intensity factor range (ΔK) over the ΔK-interval of approximately 20 to 90 MPA√m, and environmental effects were evaluated by comparison with similar data for HY-130 obtained in air. All fatigue experiments were conducted at a maximum stress intensity factor (Kmax) < (KIscc), a stress ratio (R) = 0.1, a cyclic frequency (f) = 0.1 Hz, and a temperature (T) = 24 ± 2°C. In the absence of inhibitors, crack growth rates are enhanced approximately threefold by an aqueous environment relative to air. A comparison of results from distilled water, 0.6M NaCl solution, and 0.1N HCl solution suggests that the crack growth rates are not influenced significantly by chloride ions or acid conditions (pH ≃ 1.0). Under alkaline conditions (pH ≃ 12), the crack growth rates are between those observed in air and in distilled water, acid or saline solution. The chromate ion is an effective corrosion fatigue inhibitor for HY-130, as indicated by the coincidence of its da/dN-versus-ΔK curve with that of air. All of these crack growth rates converged at higher ΔK values. Applied cathodic potentials increased crack growth rates beyond those observed under freely corroding conditions in 0.6M NaCl solution. This enhancement in crack growth rates is only observed at ΔK-values above 30 to 40 MPa√m. The results suggest that hydrogen is involved in the crack growth mechanism.