Dear all:
My question is how about the stress checking difference between TEE and nozzle.
I just want to limit the checking under elastic scope.

As we know, ASME31.3 can be used for TEE checking, the checking is just for allowable stress that depend on material.
As Nozzle checking, we can use ASME vIII, Division2;

Actually, Tee also is Nozzle, but the ASME31.3's checking in more simple.

who can tell me which one is more conservative between ASME31.3 and ASME VIII division2?

thanks very much!!

You might like to check this out for yourself ?

It is difficult to answer which is right or not

Both B31.3 and ASME VIII Div 2 are right .... but one may be more conservative than the other.

Tee's check is covered by Asme B31.3 because it is a problem of piping.
When you check a nozzle, the weakest part is the nozzle, not the pipe. And the nozzles are covered by other codes, depending on the equipment.

OK, For one unreinforced tee(fabricated ) , whether can we call it a nozzle?
I think we can since the structure is same as a nozze.
since in ASME31.3 It is dealed as piping, whether we also can treat it as piping if one vessel is in ASME31.3 SCOPE?

Question ... If you build a pressure vessel entirely from piping components such as reducers, end caps, flanges and tees ... is it a vessel or is it a bunch of piping elements ? Answer ... depends mostly on the classification (insurance) company and the owner. Generally if it has a piping line number, it's a pipe, if it has a vessel number, the vessel design code applies. It's not a pipe stress engineer's job to be defining or guessing these things.