A.R.C. Markl in his paper "Piping Flexibility Analysis" set the Expansion Allowable Stress Range so as not to exceed twice the yield stress, times a safety factor, times a cyclic reduction factor minus the mean stress. The total stress range (expansion plus sustained)was set as twice the yield stress.
I don´t know how the equation for the Expansion Allowable Stress Range was set:
SA < f(1.25 Sc + 1.25 Sh) - Sl.