When the user the pipe correkt modeled, then he
place at the point where the stiffness changed a node.
Ok, you have then two short zylinder between weld
and at the beginn reducer an end recucer.
Sorry i have allways a sketch or a draw for the recucer in nuclear power plants.
Sure when you take sif = 2 then this is conservativ, but i think more realistic stress
calculation is better.