What is the basis for conducting a gas-tightness test on the tube side or shell side of a heat exchanger?
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The heat exchanger is subjected to a gas-tightness test; for example, the medium in the shell side is benzene, while the medium in the tube side is water. The pressure in the tube side is higher than that in the shell side. Should the airtightness test be conducted in the tube side or the shell side? If airtightness is ensured on the shell side, is it because the medium is benzene (which is highly toxic) that this is done on the shell side? If airtightness is ensured on the tube side, is it done so because the pressure on the tube side is higher than that on the shell side? Whether to conduct a gas-tightness test is definitely related to the toxicity of the medium. Should airtight sealing be done at the stage where the toxic medium is present, or only at the stage where the pressure is high? Also, some heat exchanger fluids are non-toxic, but they still require leak testing for air or ammonia. Why? Also, when performing a leak test on the shell side, it is to check the tightness of the weld joints between the heat exchange tubes and the tube sheet. So, when conducting a leak test on the tube side, which parts are being checked? I would appreciate it if some experts could help answer this question. Thank you.
Article 6 of the SH/T3542 Code for Construction and Acceptance of Static Equipment Projects stipulates
Regarding the situation described by the poster, first, it is necessary to increase the hydrostatic test pressure for the shell side; this value can be set at the same level as that for the tube side. Meanwhile, the stress level on the shell side during the pressure test should be checked based on a factor of 150. Its purpose is to prevent leakage at the pipe ends during the pressure test of the pipe train. After the pressure test is passed, a airtightness test is conducted. The airtightness test is more sensitive than the pressure test, allowing it to detect issues that cannot be identified by the pressure test. For multi-chamber equipment, the airtightness test is conducted in the chamber where the medium is located. As for the case where the medium is non-toxic, a gas-tightness test is also required; it is likely that mixing of two types of media is not allowed, with emphasis being placed on the properties of the medium itself.
So what if the shell-side pressure cannot be increased to the level required for the tube-side hydrostatic test?
In practice, leaks in heat exchangers usually occur at the joints between the tube sheet and the tubes, and airtightness tests are also conducted at these locations; leaks can thus be detected in the shell side. Gas tightness of the tube bank means checking the tube box and heat exchange tubes
The airtightness test is a type of leakage test; a leakage test is conducted for each section through which the medium passes. When the pressure used for the hydraulic test of the tube side is higher than that used for the shell side, performing an ammonia leak test on the shell side is an effective method to determine whether there are leaks at the joints between the tube sheet and the heat exchange tubes. This method has nothing to do with whether the medium in the shell side is toxic; however, it matters if the medium in the shell side is explosive or highly reactive. In cases of high hazard, and when the hydrostatic test pressure for the tube side is higher than that for the shell side, the ammonia leak detection test can be effectively carried out concurrently.
I checked sh3542, but couldn’t find any specific information regarding this issue
The airtightness test is determined based on the toxicity level of the medium, and it is not necessary to conduct it for all of them. The voltage withstand test is always carried out together, or in other words, the voltage withstand test serves as a replacement for the airtightness test. The sequence of pressure testing for heat exchangers of different types also varies, and it shall be carried out in accordance with the requirements of GB/T151. As for whether it is the chamber used as a medium or all the chambers, pressure vessels are counted on a per-unit basis, not per chamber; therefore, counting them on a per-unit basis is the correct approach. However, counting them per chamber is also not wrong. The system airtightness test can serve as a substitute for the equipment airtightness test.