As Richard says this is not for CAESAR II. Using FEA you may get it wrong also. Item is in creep range and you have to get it right. I would not risk this critical item. There are also manufacturing and welding issues. Find a supplier who has done this before and talk to them.

If this happens to be your first P91 job or first main steam line please talk to power station steam pipe designer. There is a long list of issues that have to be considered.