The reason why they use water instead of air for hydro testing is because when a tank fails it usually cracks open. A tank full of water will crack, make a big mess of the test site, and that's all there is to it.
If there's more than a little bit of air in said tank when that failure happens, the air expands and rips chunks out of the tank as it escapes through the defect. Though I have seen hydro tests performed that went solid with water and then did the final pressurization on air due to the low pressure needed, its still more hazardous than an all-water test if the vessel does fail.
I guess if you can do it outside with some long hoses, you'd probably be okay. If it cracks the water will just start spraying out, and you'll have time to turn it off and get away from it till it stops.
At the same time, I doubt that it would cost more than $200 to get even a large tank like that certified aside from transportation costs. A brand new 240 gallon 200 PSI MAWP vessel can be obtained from Manchester tanks for as little as $900 + shipping. There would be no reason to have an old one recertified if it cost a lot of money to do.
Also, it may be possible to get it recertified where it stands. There are portable test apparatus after all, if the tank can be moved outside long enough for the test to take place you might not have to transport it. Instead the inspector will come to where the tank is and bring the hydrotest pump and gauges with him.
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So Luis,
Keep in mind I said "may" not "will", nor "should". And that I did not say "condemn", but "unfit to return to service" which could also be "remove from service" or more appropriate "rejected". Both differ from "condemnation" with regard to what options are still open to both the facility and the owner of the tank.
Tank characteristics very from design to design. Some of the PST E series are notorious for having been incorrectly condemned. PST's solution was that you use an allowed "leak check" to pre-stress the tank to 85% of hydro pressure. And still, even after that, many of them will test in the 9%+ PE range. If it was one of these that we are talking about I could or can agree.
However, if we're talking about your average AL80, the norm is to see 0% PE. The idea is to identify tanks that are loosing their elasticity "before" they fail catastrophicly. If a tank is identified as being that close to the pass/fail point with regard to PE and has other characteristics that are also indicative of a tank that is at or nearing it's retirement point, it would be remiss of the tester to not bring it to the attention of any and all involved. To simply stamp the tank as "A O.K." and send it out the door without notation could result in a catastrophy or at the very least a continuation of procedures that are destructive to a tanks longevity.
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