Pressure testing issue for the tube ends of floating-head heat exchangers
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When testing the pipe ends of a floating-head heat exchanger under pressure, a fixture is used to seal the shell side; the pressure is increased to the experimental level to check that there are no leaks in the pipe ends. However, there is slight leakage at the sealing point of the fixture. Some people say that when testing for leaks in floating-head pipe ends, it is sufficient to check whether the pipe ends themselves leak, as the sealing point of the fixture is not considered a sealing surface, so slight leakage is not a problem! I would appreciate your advice, everyone!
It can be said that since the pressure testing fixtures (dummy heads) are temporary, and sometimes one dummy head is used for multiple types of heat exchangers, coupled with installation quality issues, leaks can occur occasionally. But as long as the pressure remains stable for a sufficient period, if it drops, simply reapply pressure to maintain it. As for heat exchange tubes, eddy current testing or individual hydrostatic testing is generally carried out; as long as the quality control procedures are followed, the tubes themselves will not leak. Therefore, check the inspection records of the heat exchange tubes; if there are no issues, slight leakage at the seal of the fake cap and no leakage at the tube ends is acceptable.
The pressure test is for the equipment, not the tooling. As long as the device is qualified, that’s fine.
It’s quite normal for leaks to occur in the test fixtures (dummy covers) used during pressure testing. This may be due to insufficient water flushing of the sealing rings. As long as the test pressure can be maintained for a certain period of time, or if the pressure drops only slightly due to leaks, there’s no problem. However, if the pressure drops rapidly, it’s necessary to reapply pressure, aiming to reach a level slightly higher than the test pressure. For instance, when conducting a hydrostatic test on each individual tube in a heat exchanger bundle, the pressure is typically raised to 15 MPa. Alternatively, one can try flushing the sealing rings with more water. There shouldn’t be any problem.
If I were an inspector, I wouldn’t allow leaks to occur due to the use of testing fixtures; it’s such a simple task – why would we want to disappoint the inspector over something like that? !
Pressure testing requires tooling; fabricate a flange temporarily!
Test fixtures are not allowed to leak, as clearly stipulated in the pressure resistance tests outlined in the \"Solid and Liquid Equipment Regulations\".
The key is to see whether pressure can be maintained; if not, the test results will also be deemed unsatisfactory. If pressure can be maintained, then the focus of inspection is on the pipe fittings – as long as there is no leakage from these fittings, the requirements are met.
If there is a leak during the pressure testing, can the pressure be maintained? Definitely not – it fails the test
That’s what they say, but sometimes the client gets too picky, which leaves you with no choice
Sometimes, the deformation of the tubes and asymmetry in the shell cause the sealing elements to fail, making leaks inevitable; of course, this is a rare occurrence. This kind of problem often arises in heat exchangers that have been in operation for a long time and are exposed to relatively high temperatures.