RE: PWHT REQUIREMENT warranty/liability

-----Original Message-----
From: John [mailto:jru@telusplanet.net]

Next, I'm assuming that your welding a spool piece to a "buttweld valve"? The buttweld valve is designed to have a longer center to end dimension directly relating to welding. This valve is a called a "repair valve" because the spool can be cut, the buttweld valve dropped in, and welded without the need of flanging.

Valve specified to either API 600 or B16.34 are not manufactured with a welded piece of pipe. If it does, then a mods/alteration has been performed - then what you got is a repaired valve and there's a chance its been used before and that the seats are worn and its been lying in a bone yard for quite some period of time. If the supplier cant produce traceability and test certs then i will not even consider it.

I normally specify a flex-wedge disc for gate over 6 NPS. If the service is a critical/severe then i will select an API Trim No. 8 (hardfaced). Factored in the rating (which determine the face to face dimension), sourced the valve from a quality maker, throw in API 598 plus PMI as a req't and used only a qualified WPS and welder then probability of damage to the seat is almost nil. I still would like to know what's with the 14.27 mm pup piece - i mean why not sch60?

I guess im skirting the issue. the question - Is there a clause in B31.3 as substitute to PWHT. Yes - 331.2.1 Alternative Heat Treatment - normalizing or normalizing and tempering or annealing. Im more familiar with the NBIC - temper bead welding or higher preheat. I did solution annealing for Cr-Mo tube heater but it has nothing to do with thickness (residual stresses)but rather with carburization. Least we forget, code is not letting you off easy with this alternative clause - check out 331.2.2 requirement before proceeding. Received on Tue Jan 21 23:44:00 2003