Note that the high cycle displacement condition is a candidate for using the f factor for an unlimited number of cycles that was added to the 2004 edition of B31.3, f=0.15. If the stress range for those conditions is less than SA with f=0.15, they are not included in calculating the equivalent number of cycles.

I would think that you would design your branch connections etc such that their natural frequency would be significantly higher than the 1/3 hertz excitation frequency (20 waves per minute) in which case the DLF would be essentially one.