Standards for ensuring airtightness of distillation towers
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What constitutes a pass for a gas-tightness test of a distillation tower? For example, when pressurizing the nitrogen in the pressure tower to 0.65 MPa, what is the acceptable level of pressure drop within 24 hours, or what is the acceptable rate of pressure drop per unit of time? If the charging pressure is different, won’t the pressure drop also be different? For an atmospheric pressure tower pressurized to 0.1 MPa, what is the acceptable rate of pressure drop per unit time?
One should not rely solely on pressure drop; a gas-tightness test should be conducted on all sealing points (using soapy water), the leak locations should be identified, and the leaks fixed.
The gas leakage test shall comply with the following requirements: a) The leakage test shall be conducted after the pressure test is successful, and air is preferably used as the testing medium； b) The leakage test can be carried out simultaneously with the equipment commissioning ； c) The key points for inspection in the leakage test should be the valve stuffing box, flange or threaded connections, vent valves, exhaust valves, drain valves, etc ； d) Pipelines that have passed the pressure test and remain undismantled after the test may be exempted from the gas leakage test. Charge the system pressure to the design pressure and take readings after 24 hours. The acceptance criteria are: a pressure drop of no more than 1% of the test pressure value, and no more than 0.1 MPa.
This post was last edited by wawjia on 2010-12-3 at 14:12. Reply to 3# wawjia: Thank you for your reply. We have ensured airtightness at all the flanges, valves, and instrument connections in our pressure tower; however, when the pressure was raised to 0.65 MPa, it dropped to 0.06 MPa after 24 hours, which does not meet the standards. When testing the airtightness using soap at a few manholes, slight foam appeared but no bubbles were formed. There is no way to tighten these connections any further. Will there be leaks during operation? Thanks for the advice~! Also, manholes and flanges are installed and tightened in summer – could temperature have an impact on these?
Reply to 4# 20057614: The pressure during charging is also approaching the target value; it can still be increased further. The designed pressure for the pressurization tower should be 0.8 Mpa. White foam can also be seen at the manhole; this is likely not appropriate. Something else needs to be done – the gasket can be replaced and tightened again, and there are specific techniques involved in tightening it as well. If there is very little white foam, it can be considered acceptable. There’s nothing to do; maybe everything will be fine once the methanol gets in. The viscosities of air and methanol are different, right! The pressure drop over 24 hours is a bit high; if the flanges are not leaking, it’s likely that the valve isn’t closed properly. It’s recommended to redo the installation – the pressure drop is almost 1 kilogram higher!
At relatively normal temperatures like those in distillation, there is no need to perform cold or hot tightening of bolts