Hallo Dave,
Dave I too faced this probelm
There was no change in the sustained allowable stress .For both true and false condition the sustained allowable stresses remain unchanged .
In my case the pipe was A335 P11(CrMo) and the temperature was 454 deg C.
W value comes out to be 0.95 as per Table 302.3.5 of B31.3 2010 edition.