This project entailed refitting the Paris fatigue constants to data from the IM-3-2 project. The purpose of this work is to provide improved material constants for inclusion in a future edition of API RP 1176. The original fits suffered from several shortcomings, including the inadvertent commission of a statistical fallacy called Simpson’s Paradox. In addition to new Paris equation fits to the IM-3-2 data, this report contains fits to the Walker equation, which enables operators to account for differences in growth rates at high and low R-ratios, where R is the ratio of minimum to...
This project entailed refitting the Paris fatigue constants to data from the IM-3-2 project. The purpose of this work is to provide improved material constants for inclusion in a future edition of API RP 1176. The original fits suffered from several shortcomings, including the inadvertent commission of a statistical fallacy called Simpson’s Paradox. In addition to new Paris equation fits to the IM-3-2 data, this report contains fits to the Walker equation, which enables operators to account for differences in growth rates at high and low R-ratios, where R is the ratio of minimum to maximum pressure in a given cycle.