What are the experience out there for PWHT of tubesheets?

[vesselguy]

Hi All,

Just want to hear the problems or experiences people have had during and after PWHT of thick tubesheets > 4" thk. I never had experience with PWHT of tubesheets before and just like to hear some experiences to get a heads up.

My situation right now is P9 tubes are all strength welded to the 410S clad 8" thick tube sheet before PWHT. I am concern about wrappage of the tubesheet and possibly delamination of the cladding due to differential expansion across the clad and parent metal boundary.

 

[grampi1]

1)Lamellar tearing of the TS/Shell weld due to differntial expansion caused stress.
2)Tube leaks if the tubes thermally expand against a fixed end.
3)Caustic cracking if shellside alkaline water (boilers) is not removed prior to PWHT

Have been personnaly involved with cases of 1 and 2 and have read about #3