Appendix A of the ASME Boiler and Pressure Vessel Code, Section XI, contains a reference curve for fatigue crack growth rates in air in ferritic steels that was established in 1973 with a limited amount of data. In the past 15 years, many additional data have been collected that do not agree with the trend exhibited by this original reference curve. In light of these new data, an analysis has been undertaken to re-evaluate the fatigue crack growth rate curve in the Code. As a result, an improved reference curve that considers the dependence of crack growth rate on R-ratio and ΔK has been developed. This paper presents the technical basis for the improved curve, some details on the analysis used to determine it, and comparison of the current Section XI Code with the available ferritic steel database and the new reference curve. The format proposed for adoption of the new reference curve is presented, with comments on the practical effect of the proposed change.

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