Purge a gas main
Purge a gas main
(OP)
How can I purge air from a gas main (the gas is lighter than air) I assume I need 2 holes in the main, but is the position and size of these in/out holes important.
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RE: Purge a gas main
The fact that the gas is lighter than air is overcome by introducing gas into the line at a rapid enough rate so that there is minimal mixing and the gas pushes the air out rather than combining with it.
As far as the location of "holes" ideally they are at the extreme ends of the line so that the gas can fully push out all the air. Ieally each "hole" has a valving arangement so that you can control the amount of gas during the purge as well as close the outlet valve so that no air can get in once you quit the purge.
RE: Purge a gas main
RE: Purge a gas main
We sometimes do use pigs in a purge to remove the gas from a line that is to be abandon, this is partially done to remove any liquids that may be present.
If the line has pig launching and recieving facilities at each end then pigs could be used as part of a purging process. As you mention they probably won't completely eliminate mixing (but it should help), so the purge should continue for an additional time after the pig is recieved.