"Jon Elson" wrote in message
...
Ignoramus335 wrote:
I was thinking overnight. If the issue is fatigue from vibration, what
if I take the motor and pump off, set them up somewhere else, weld and
test the tank, and use it as air receiver tank at a slightly lower
pressure (say, 120-150 PSI).

Then further fatigue will not be an issue, as there will not be
further vibration.
It's not fatigue from the pump vibration, it is fatigue from the expansion
of the tank under air pressure. Every time you pump up the tank, it
expands a few thousandths of an inch. Any weakness or corrosion
concentrates that stress.

Jon

I disagree with that, Jon, based on data from the AWS Pressure Vessel
welding reports I've seen over the years. The expansion/contraction due to
pressure increases and decreases is a minute fraction of the fatigue loads
imposed by vibration.

True fatigue, as I said, is a very strange phenomenon. There are all sorts
of failures we commonly call "fatigue," but true fatigue often behaves very
differently from what many people expect. It's the product of number of load
cycles imposed at some large fraction of the elastic limit, and it varies
widely by material type. For aluminum, for example, that
expansion/contraction due to pressure changes, as in a jet airliner, can
indeed fatigue the material to failure. In steel, that isn't likely to
happen. Steel is vastly more resistant to fatigue than aluminum is. Fatigue
cycles to failure for steel usually are measured in the tens of millions of
cycles. That's a lot of expansion and contraction, but maybe only a few
years of vibration cycles, given the normal uptime on a compressor in
commercial service.

--
Ed Huntress

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Ed Huntress