Fatigue testing and analysis of cathodically protected notched specimens tested in a fully aerated aqueous 3.5% NaCl solution

Fatigue test results of notched low alloy steel specimens tested in a fully aerated aqueous 3.5% NaCl solution with cathodic protection (CP) are presented. A CP potential of −1050 mV Ag/AgCl was used. This work extends the testing presented in Wormsen et al. (2015a, 2015b, 2015c), covering fatigue testing of smooth and notched low alloy steel specimens tested in-air and smooth specimens tested in 3.5% NaCl with CP. The specimens were machined from material cut from a hollow, thick-walled AISI 8630 M low alloy steel forging with an actual yield and tensile strength of 632 MPa and 771 MPa, respectively. The reduction in fatigue life for the notched specimens tested in the 3.5% NaCl solution with CP relative to air was found to be consistent with the reduction in fatigue life for the smooth specimens in Wormsen et al. (2015b). It is considered that a design S-N curve for seawater with CP can be constructed from the smooth specimen in-air S-N curve using an environmental reduction factor of 2.5 (HSE, 1999; BS 7608, 2014) for subsea components of this steel subjected to high cycle variable amplitude loading. The fatigue test results seem to indicate that a larger environmental reduction factor may be required for constant amplitude loading when the maximum stress in the cycle is higher than the yield stress.