On Tue, 1 Jan 2008 09:28:01 -0800, "Stuart & Kathryn Fields"
wrote:

Morgans: According to everything I read in my research for the article I
wrote, the "Quick stress relieving" by the few seconds of OA after a TIG
weld do not effectively relieve the stress and can actually cause a
weakening of the weld joint. There appears to be quite a bit of truly
scientific experimentation to support this view. As a retired engineer, I'm
more prone to accept the scientists report over the anecdotal evidence from
more questionable sources. All that said, I can relate to failures that I
saw as the result of a crash of Chrome Moly airframe. Tube failures near a
cluster showed a separation that occurred just a short distance (1/4") from
the weld that was relatively clean and very even and roughly resembling a
fatigue failure zone. The Richard Finch that I referred to in an earlier
post wrote the book called Performance Welding and cited his experience at
Aerostar. I'm going with him and his belief supported by the research I did
and will not allow an OA torch near my TIG welded joints.
BTW, with the exception of some welds on my SS exhaust, none of my TIG welds
which includes fuel and oil tanks and the SS railing on a 35' Sailboat have
shown any cracking. None of these had OA "Stress Relief".

Stu
"Morgans" wrote in message
news

"Stuart & Kathryn Fields" wrote

Thanks Rich: That coroborates all the stuf I found thru digging thru
University research papers, certified welding instructors, Metalurgical
studies and a bunch of writings of people like you and the EAA tech
counselor. All that said, I have an IA friend that still insists on the
OA " normalizing" or "stress relieving" after a TIG weld. However, not
on my helicopter.

So, do you think that the tig welding does not induce the stresses, and
therefore not need the quick OA "stress relieving" or what? I'm
interested in the reasons you came to this conclusion.

I may need to make cromolly engine mount, but the rest of my dreambuilt
airplane will not require any normalizing.

I hear wood airplanes do very poorly with an OA torch held at their
"clusters." ;-)
--
Jim in NC


The commonly accepted knowlege on this subject is to use a low alloy
filler rod when tig-ing 4130, in still air, and no post-heat stress
relief.
The low alloy filler draws some alloy from the base metal (tubing) and
the fillet is thicker than the substrate, so the total strength of the
"low strength" weld is equal to or superior to the base metal. The
base metal is "drawn" - it is less hard, and slightly weaker but less
prone to cracking, so you get a good, solid, reliable joint.
Cracking is extremely rare when the structure is built this way.

--
Posted via a free Usenet account from http://www.teranews.com