Discussion on detection methods for internal leakage during airtightness testing
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For detecting internal leaks during the airtightness testing process, we usually start with positive pressure testing; this can be easily carried out using soapy water or electronic leak detectors, by measuring the pressure drop over a certain period of time. But for negative pressure systems, how is it detected? If, after system isolation, the set negative pressure is reached, then isolate it. Then, over a certain period of time, the system’s pressure increases; at this point, the soap water test for identifying leaks is no longer effective. So how do we determine where the leak is? Should we tighten every flange and connection point in the system one by one, and then take measurements repeatedly? What are good methods to quickly identify leaks? I hope everyone can talk about how you did it!
Clean the flanges thoroughly, then seal them by wrapping tape around the upper and lower flanges; the tape at the leaking flange will be distorted due to suction, making it easy to detect the issue
For negative-pressure systems, a positive pressure is used for airtightness testing, with the pressure generally not exceeding 0.2 MPa; soap water can be used to detect leaks, which can then be repaired. Once negative pressure is applied, the integrity of the system is usually maintained.
Generally, a vacuum system should first undergo a positive pressure leak test; the leak points must be fixed before a vacuum test can be carried out. In other words, a vacuum test can be performed, but pressure testing is the best method for detecting leaks.
I agree with everyone’s views; it is also stated in the specifications for the installation and acceptance of industrial metal pipes that negative pressure systems are tested for leaks using a positive pressure of 0.2 Mpa!
The vacuum towers I have experienced include vacuum distillation towers for atmospheric and vacuum distillation, degassing towers for the hydroprocessing of C5 hydrocarbons, and degumming towers for the hydroprocessing of C9 hydrocarbons. First, a positive pressure airtightness test (using soapy water) is carried out, or the leakage rate formula is used for calculation. (A=100/t). A being less than or equal to 0.5% within 24 hours is considered acceptable. In the formula: P2P1 and T1T2 represent the absolute pressure and absolute temperature (K) at the start and end of the test, respectively, while t is the test duration in hours. Finally, vacuum pumping is used to determine the leakage rate.