Helium leak testing for heat exchanger tube joints
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This post was last edited by “Sad Landscape” on December 30, 2015, at 18:51. I have a heat exchanger; the design pressure for the tube side is 3.0, and the medium is ammonia. On the shell side, the pressure is 0.6, and the medium is water. At that time, it was decided not to conduct a hydrostatic test on the shell side; therefore, a helium leak detection test was chosen (our factory does not have ammonia leak detection equipment). However, the customer raised a question: since the leak test involves evacuating the shell side before conducting the leak detection, could ammonia leak under operating conditions of (2.5, 0.3)? They want us to conduct helium leak testing under actual operating conditions…… I’m a bit puzzled now. According to the first method of helium leak testing, pressure is applied to the tube side and then testing is carried out (I’m just talking theoretically); the pressure applied is only 0.25 times the design pressure, or 0.103 MPa, and even if that passes as satisfactory, it still… So, can this really guarantee no leakage when in use? I checked, and it seems that for ammonia leak testing, there is no requirement to pressurize to the design pressure either. . . I need a solution. . . . The main problem at present is that the medium is ammonia. . . Even if the test with low-pressure ammonia is successful, how can we ensure reliability when it’s actually in use?
Helium has a strong permeability; it can pass through leak paths even at very low pressures.
In terms of accuracy, helium leak detection is more precise than ammonia leak detection; as long as you carry out vacuum pumping followed by helium leak detection, there will be no problems as long as the leakage rate remains within acceptable limits. Also, may I ask if the device was covered with a shield after vacuuming was applied to the shell side? Furthermore, have helium leak tests been conducted on the pipe fittings before? What was the pass rate, and were the requirements strict?
Helium leak test – there should be no problem
The relationship between this helium detection and the pressure you specify isn’t that significant; as long as there is a leak, the helium detection can identify it with high precision. If that’s not possible, conversion formulas can be used to prepare the test report – that’s my personal opinion
A leak test is a test used to check whether a device has any leakage defects. Whether it is ammonia or helium, or some other medium, what is utilized is the penetrating ability of that substance, and it has nothing to do with pressure. To use an analogy, if a bamboo basket doesn’t leak when used to hold water, it will surely work fine for holding beans as well. Then it doesn’t matter how much water is installed here; if there’s a leak, even a little bit of water will leak out. As long as you conduct a thorough inspection, the amount of water doesn’t matter. Therefore, when testing for leaks in equipment, it is sufficient to have the medium fill the space; any leak will definitely be detected. Ammonia leak detection uses different concentration ratios, simply to increase the sensitivity of the detection. The difference between 1 drop per second and 1 drop every 10 seconds is not the difference between no leakage and leakage. The same is true for helium; the reason for applying some pressure is to change the rate of leakage from one drop per 10 seconds to one drop per second. The sensitivity is extremely high, whether for ammonia or especially helium. The specified pressure is more than sufficient; the leak test and pressure test serve no purpose. The pressure test is used to check strength, so a leak test is not necessary, nor is a high pressure required for that test. :)
Your customers don’t understand either that molecules have different sizes; a system may not leak when subjected to a water pressure of 300 kilograms, but it might leak under a hydrogen pressure of 10 kilograms. Currently, helium leak detection is quite sensitive. It’s just a bit difficult to locate