Hydro Test - The Home Machinist!

Post by pat » Fri Dec 14, 11:58 am

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The most commonly applied pressure for hydro testing is 150%. However, certain individuals may opt for even higher pressures in the case of newly installed boilers. The primary objective remains the identification of leaks. A 150% pressure test does not guarantee that components like firebox sheets and stay bolts, which are showing signs of degradation, will be detected. I’ve personally observed two locomotives with firebox sheets measured down to just 1/32" that passed hydro tests until the moment they ultimately cracked.

During my tenure as a club boiler inspector, I followed a method wherein the pressure is maintained long enough to facilitate a thorough visual inspection. It is worth noting that with cold valves, there tends to be some leakage, which compromises the ability to maintain pressure consistently without focusing solely on the bare boiler structure.

After conducting hydro tests, I preferred to examine the safety valves in their cold state to ensure they opened correctly. It was not unusual for a locomotive with two safety valves to have the higher-value stick due to infrequent opening. State inspectors prefer to witness these being tested under steam conditions, but I have always completed my inspections prior to notifying the state.

During club inspections, the most common failure I encountered was leaking tubes, whether from rolled tubes leaking at the firebox end or mild steel tubes that had corroded extensively. I never had to deny anyone the chance to run their trains. In the event of a leakage, owners typically opted out of running after observing the issue. While I handled minor leaks, such as those running down the tube sheets, a bit of beading at the tube's end was often permissible. In addition to leaking tubes, most articles and club guidelines I encountered emphasized the importance of monitoring for popping stay bolts, which I never personally detected. Last year, I identified a leaking stay bolt weld that had been overlooked by state inspectors.

During testing, I also assess the sight glass and the gauge, ensuring that every component subject to steam pressure is included in the evaluation. If a gauge lacks adequate pressure range, I recommend removing and plugging the respective connection.

For more information, please visit hydrostatic test pumps.

So Luis,

It's crucial to remember that my use of "may" does not imply "will" or "should." I did not mention "condemn," but instead referred to the tank as "unfit for return to service," which could mean "removing from service," or more accurately, "rejected." Both terms hold different implications regarding the options available to both the facility and tank owner.

Tank characteristics vary widely across designs. Some models, like the PST E series, have gained a reputation for being improperly condemned. PST recommends performing an approved "leak check" to pre-stress the tank to 85% of hydro pressure. Yet many still register a PE range exceeding 9% after such tests. If this applies to your tank, I would likely agree with that assessment.

However, with average models like the AL80, the conventional expectation is to see 0% PE. The objective is to identify tanks losing elasticity prior to a catastrophic failure. When a tank is closing in on the pass/fail threshold regarding PE while displaying additional indicators suggestive of its nearing retirement, the tester bears a responsibility to notify all involved parties. Rushing a tank through without documentation could lead to disaster or, at the very least, extend practices detrimental to the tank's longevity.

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