"Stuart & Kathryn Fields" wrote in message
.. .
Bill: I recently did an article for our Experimental Helo magazine and
did some research on PWHT and found things like a minimum of 2hrs required
@ 300 degrees C to adequately stress relieve a weld.

Back in the early '60s I worked in the pipefitting shop at Todd shipyards.
Along with the repair work, we were building two new DDE's (Destroyer
Escorts). They were powered with steam turbines running 1500# of steam
pressure at 1000 degrees F. (or so).

The steam piping was Chrome-Moly tubing from 1" IPS (1.315" dia.) up to the
big 6-8" stuff. All of it was welded with TIG and then stress-relieved. We
had a dedicated area of the shop set up for that process. The pipes were
wrapped with asbestos sheeting followed by water-cooled electrical cables.
More asbestos was wrapped on top.

The cables were hooked to a large machine which sent alternating current
through them, inductively heating the piping within the coils. I don't
remember the temperatures or time involved, but they were recorded on chart
recorders. The process lasted many hours - even overnight IIRC. They were
heated to an initial, high temperature (700 F?) and then slowly cooled. The
records became a permanent official part of the piping's history and
pedigree - much like the documentation of aircraft components.

It was a job well-suited for the older, disabled steamfitters as it was
light work but demanded experience and meticulousness. There are few things
more scary than a cracked flange weld on a 6" high-pressure steam pipe at
sea. The escaping gas will easily slice a leg off at the thigh, cauterizing
the wound nicely.

Happy New Year!

Rich S.