On Sat, 29 Sep 2007 12:47:36 -0500, Don Foreman
wrote:

On Wed, 26 Sep 2007 12:11:06 -0500, Ignoramus25760
wrote:

On Wed, 26 Sep 2007 12:02:17 -0500, Don Foreman wrote:
On Wed, 26 Sep 2007 08:37:25 -0500, Ignoramus25760
wrote:

I saw something strange on Monday. A big horizontal compressor tank,
with nice old blue paint on it. It is a 25 HP reciprocating Dresser
LeRoi compressor written off by Fermilab, surplused as "scrap". It is
not even a compressor, it is a head separate from the tank as a pile
of garbage.

It is probably rather broken, though I have no way of knowing. It is
also huge.

Here's my question.

The horizontal 120 gallon tank has feet welded to it, looks like stick
welded out of position. The welds are not painted at all, and clearly
have this blue paint burned around the welds. So they welded the feet
on themselves, not too long ago.

I thought that you are not allowed to weld stuff to tanks like this?
That welding stuff to air tanks could lead to some bad failures,
stresses, etc?

Would I be correct in concluding that the tank is no longer usable for
compressed air, even if it passes a hydraulic pressure test?

i

That would be the safe course.

That said, how do you suppose those tanks are made? They're welded! I
have welded on compressed air tanks. No problems. But you don't know
if the guy that did the welding on the tank in question was any good,
or if he tested it after welding. Or, for that matter, that they
used it as a pressure vessel after welding since it was separated from
the pump.

Welds near the bottom can burn the galvanizing off the inside,
creating a site for condensate-caused rusting from inside out.

Don, I thought that compressor tanks are heat treated after
welding. That would relieve stresses and such. Since you welded
compressed air vessels, maybe you know the answer, I would lova to
know myself.

i

I don't know. Some might be. I knew a boilermaker who made big tanks
out of 5/8" steel plate that he pressure tested to 200 PSI. I'm sure
he didn't heat treat them. These suckers were 8 or 10 feet in
diameter. Tawk about a slip roll! They were stick-welded. Rollers
turned the tank as it was being welded, the welder just held the
stick and watched the puddle. He could probably control the roller
speed, but that probably didn't change once set to his satisfaction.


Although possible it would seem inefficient to heat treat a pressure
vessel after welding. While a heat treated vessel could be made from
thinner material the additional cost of heat treating would probably
result in a higher manufacturing cost that if simply rolled and welded
from "as delivered" stock. Can you imagine the cost of an oven to take
a 10 ft. diameter vessel? Or the amount of energy necessary to heat
it?


Bruce in Bangkok
(brucepaigeATgmailDOTcom)