• BS7910 FCGR for R < 0.5 is up to 3.6 × over-conservative for S355 in free corrosion. • Removing this conservatism could improve remaining life by 109%. • For the investigated database, statistical weighting had a negligible impact. • HAZ data fit a bilinear curve more closely, while BM data fit a linear one. • S355J2 + N subgrade displayed the highest FCGR, while S355G10 + M showed the lowest. The recommendations for fatigue crack growth rate (FCGR) in British Standard BS 7910 are based on experimental data which are multiple decades old, and the FCGR laws were constructed using data from multiple structural steel grades. The present study sought to gather more recent FCGR data for S355 steel in a marine free-corrosion environment, which can be applied for use in offshore wind turbine structural integrity life prediction. The collected data were filtered to include only valid Stage II (Paris region) data in the analyses. A method for fitting a bilinear regression curve was developed along with bias reducing weighted regression methods. The resulting bilinear trend shows up to 3.6 times lower FCGR relative to the BS 7910 recommendations for the free-corrosion environment. The analysed S355 data indicated that a bilinear fit best described the FCGR in the heat affected zone, whereas a simple linear fit was appropriate for the base metal. The S355 subgrades, J2 + N, G8 + M and G10 + M, presented considerable variance in mean FCGR, with J2 + N having the highest FCGR and G10 + M the lowest. When considered in the context of offshore wind turbine service life, the overall S355 FCGR reduction relative to the BS 7910 free corrosion curve results in a just over double life expectancy for a 4 × 20 mm surface semi-elliptical flaw size, based on the conservative upper bound analysis. This increase in life could prove invaluable for corrosion protection system repair timescales, considering the need to carefully plan the maintenance time window to avoid adverse weather conditions.
Stiven et al. (Sun,) studied this question.