I have a confusion about lift off case.
I use App. P of B31.3 in CII which takes care of operating stresses. So is it needed to check Lift off case when CII checks for operating stresses?

The Sustained and Expansion cases must still pass.

That's right.
My query is,
If we don't use APP. P of B31.3 in CII, It doesn't check OPE stresses. IN this case Suppose a Support gets lifted, we will check for LIFT OFF case by removing that support and check for stesses.
But IF We use APP. P in CII, it checkes OPE stresses.
So do we check lift off case again by removing that support and check stresses?
In both cases, I agree that all stresses(SUS,EXP,OCC) should be within alloawable.

Read the section in the Technical Reference Guide (Chapter 6) on the "Hot Sustained" case.