How to achieve airtightness in a negative pressure system
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In petroleum refining and chemical processing plants, many devices operate under negative pressure; for example, the solvent recovery tower and solvent regeneration tower systems in aromatic extraction units operate at a pressure of -50 Kpa. Moreover, due to concerns regarding the oxidation and degradation of sulfolane, strict requirements are placed on the airtightness of these systems. How can such negative-pressure systems be made airtight? If the static pressure drop is found to be unsatisfactory after evacuating the system, can the leak location be identified under negative pressure?
Install the oxygen gauge. It can only be checked in segments
The airtightness test for negative pressure systems is the same as that for positive pressure systems. After pressurizing with positive pressure, check the sealing points using soapy water to identify any leakage points and their locations. If pressure is maintained after applying negative pressure, any leakage points cannot be detected. Therefore, it is better to use positive pressure airtightness. However, attention must be paid to the test pressure to avoid damaging the equipment. To avoid oxidation, airtight sealing with low-pressure nitrogen can be used.
Positive pressure testing can be utilized, with N2 used as the medium for testing, which may help ensure that the material on the inner surface does not deteriorate.
It’s difficult to locate the leak point under negative pressure; one can only use their ear to listen for a faint hissing sound. However, given your strict requirements, this method is not suitable. But a nitrogen pressure test can be carried out; it should work. My own thoughts are for reference only.
We use the positive pressure method for pressure testing of control systems here, although the vacuum requirement here is not particularly high.
Recently, I was working on a vacuum drying project. During the leak testing, nitrogen was used to apply pressure, and then soapy water was used to identify possible leak points; first at 0.2 kilograms of pressure, then 0.5 kilograms, and finally 1 kilogram. When the leakage is severe, a hissing sound of air escaping can be heard.