Rich,
I figured out the whole thing. The allowable in "Exp" are in fact "Operating Stress Range" allowable ( as per equ P1b).

Can we have an added option in future wherein we can check Expansion Stress range alongwith "operating stress ranges" separately when the App P is activated. Also, it should be called "operating stress range" as per App P rather "expanion stress range" when App P is activated; to avoid any confusion between the two?

I quote from the help file for App P allowable reduction "The software selects this check box by default for the B31.3 code. When selected, CAESAR II performs this reduction, when applicable."

I interpreted " when applicable" as the software will reduce the allowable only & only if it meets the conditions of smys/st more than 0.8.It doesn't direct the user not to deactivate it if its not applicable.

I guess most of the users will interpret it my way.