Here's a good one for the gang to chew on.

Hot Tapping, for everyone's benefit, is where a line that is operating is cut into for the purpose of adding a branch. It is done when it is difficult for some reason to shut the header down to make the branch connection.

This poses a challenge for correctly coding the system to obtain the true displacement stress range. Since the header is at temperature, it has already completed it's displacement before the branch has been heated up. So, part of the range comes from the branch displacing as it comes to temperature. The second part of the range comes when the total system is shut down. The branch displaces back to its initial position, but it is further displaced by the header contracting to its own installed position.

In my particular case, the branch and header are going to contract along the same axis (toward the same end of the pipe rack). So, the total displacement will be a larger number.

So far, I have these cases:

I have coded the lines such that

header branch
T1: ambient Top
T2: Top ambient


L1: W+T1+P1 (OPE)
L2: W+T2+P1 (OPE)
L3: W+P1 (SUS)
L4: L1-L3 (EXP)
L5: L2-L3 (EXP)

So, what I'm having trouble wrapping my head around is setting up another load case or cases to give me the total expansion stress range. My current system is fairly simple, and I usually end up manually adding the thermal stresses for L4 and L5 together at point of concern (the nodes at the branch connection, in particular) and comparing to Sa.

However, I would think with all the combining that Caesar is able to do, I should be able to find this stress automatically with a combination of load cases.

I imagine it would be the same kind of thing if you had a line where the range of operating temperatures went both above and below the installation temperature.

Is there a definitive set of load cases to get me where I need to be?