On Sep 26, 1:37 pm, Ignoramus25760 ignoramus25...@NOSPAM.
25760.invalid 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

It might be okay. It might not. But it's very hard to know, and it's
unlikely that anyone in this newsgroup will be able to give you a
definite answer. Personally, I would not use the tank.

The danger isn't so much that the tank will fail immediately. The
danger is more that the welds will act as initiation sites for fatigue
cracks, which will grow ever so slightly with each cycle of
pressurisation and de-pressurisation, until eventually the tank fails.
This is a situation in which the quality of the welds is very
important.

I can't think of a major disaster which was caused in exactly this
way, but the Alexander Kielland oil rig disaster was very close. A
bracket for mounting an underwater instrument was welded onto one of
the bracing members of the rig. It was done without the knowledge of
the rig's designer and by all accounts it was done badly. The waves
caused the stress in the bracing member to vary cyclically, and a
crack began to grow. Eventually the bracing member broke during a
storm, allowing one of the platform's legs to break off, and the
platform to capsize.

This isn't the exact explanation of the disaster given in the
Wikipedia article, but it's the explanation given in a book I have on
the disaster, which is probably more trustworthy.

Best wishes,

Chris