This is not a simple question or something that lends itself to a simple answer.
IMO it is always a good idea to stress relieve a full penetration repair to a boiler tube sheet. NBIC allows you to perform weld repairs without PWHT, regardless of tubesheet thickness, using one of several techniques ranging from a simple preheat with interpass temperature restriction to preheat plus temperbead techniques. Type of repair depends on type of material, age of material, condition of material, thickness of material (corroded or uncorroded), temperature of the tube sheet during normal operation, stresses on tube sheet, so on and so on.
Given that, after completion of the repair weld, I think it is also a good idea to hydrotest any repairs to the tube sheet. I have found leaks that way even after the PT showed no indications. Sounds strange since hydro is not a sensitive leak test, but just happended this week.
A few cracks are through wall, but most are not. Boiler built in 1989. Tubesheet material is mild steel. I'll do a hydro after just to make sure theres no leakers. But dont want to heat the welds because of possible distortion. My AI wants all the welds heated because the ASME did so when the boiler was made. What do you think about preheating the welds before I welf them?
I don't believe PWHT is necessary on in-service tubesheet weld repairs. Preheat is a definite requirement, for this application 200 deg F.
Regarding hydrotest, I would not perform a "code" hydrotest, instead I would perform a liquid pressure test. I don't believe in having an in-service component subjected to a "code" hydrotest (1.5 x MAWP).
