I don't know exactly your situation, but the first question that comes to mind is: Why bother purging the entire length of the pipe which you wrote is 20' in length???
Why not either make two purging dams and shrink the overall length of the purged space with respect to lessening the volume required to be displaced with the argon purge...
for example, one can shrink the overall purged length to 2' as opposed to 20' by incorporating a set of purge dams and depending on the budget, one can either use water soluble/rice paper purge paper dams, or two inflatable dams, or baffles/plugs made up of very high heat resistant material which are attached to each other via the use of a chain and co me in a variety of sizes with respect to applicable diameters in question, and can be easily removed from the post welded location via deflating and/or pulling the baffles/plugs/dams out towards the direction of the remaining opening @ the opposite end of the pipe length. ;) IMHO, a much better, cost effective method to use if one is going to be fitting and welding a lot of this type of work. ;)
Check out these links to learn more, unless you're already familiar with this type of equipment and pipe welding accessories:
http://www.tubenet.org.uk/technical/whypurge.htmlhttp://www.intercononline.com/welding/purgpapr.htmhttp://www.intercononline.com/welding/mainpurg.htmhttp://www.dissolvo.com/welding_instructions.phphttp://www.abpaper.com/http://www.thefabricator.com/article/consumables/dam-the-purge-gas-and-full-speed-aheadhttp://www.aquasolwelding.com/products/papertape/vshttp://www.aquasolwelding.com/techtalk/http://www.rubcons.com/saf/products_safety_purgedams.php3http://www.gowelding.com/met/purging.pdfhttp://www.huntingdonfusion.com/downloadfiles/LTAPF.pdfI almost forgot about these folks also:
http://www.cob-industries.com/argweld.aspx?utm_source=Google&utm_medium=CPC&utm_term=purge%20dams&utm_campaign=Argweld&gclid=CKmMkr6tv6ECFRRM5Qod0QigAwWell, that's about it for now, yet I'm sure there's more options available if one searches further online. ;) Hope this helps! ;)
Respectfully,
Henry
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