Hydro Test - The Home Machinist!

Post by pat » Fri Dec 14, 11:58 am

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150% is most common. Depending on the service factor some people like to go higher with a new boiler. Mostly you are looking for leaks. A 150% hydro won't reveal firebox sheets and stay bolts that are nearing failure. I have seen two locomotives fire box sheets down to 1/32" in places that passed a hydro up to the day the sheets cracked.

In the tests I did as a club boiler inspector and what the state does since they took over is to hold pressure long enough to do the visual inspection. There will be enough leakage through cold valves that unless your looking at just the raw boiler you can't really saw hold pressure for x minutes.

After hydro I liked to test the safeties cold to know they opened. It wasn't uncommon when a locomotive had two safeties for the higher valve to stick if it rarely opened. The state inspectors want to see them open with steam. It's o.k. for me as I've always done my own inspection before I call the state.

Failure when I did club inspections was typically leaking tubes. Either rolled tubes leaking on the fire box end or mild steel tubes that had corroded through. I never had to tell anyone they couldn't run. If there were leaking tubes to a man as soon as the owner saw it he said he wasn't running. Leaking as in running down the tube sheets I'd fix. A little water beading at the end of the tube we let go. Aside from leaking tube all the articles and club procedures I've read talk about listening for popping stay bolts. I never heard any. I had a leaking stay bolt weld last year that the state missed but I saw.

I hydro the sight glass and the gauge. I like to have everything that will be under steam included in the test. If the gauge doesn't have enough range take it off and plug the connection.

For more information, please visit hydrostatic test pumps.

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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