Purge Times

By mcianchette Date 04-22-2002 20:15

I am looking for a complete and comprenhensive chart or information that shows the proper purge times and rates for various sizes of pipe. Any information would be greatly appreciated.

By MBSims

Date 04-22-2002 21:33

You can find a speadsheet on the website below that calculates purge times:

http://www.sperkoengineering.com/html/welding.htm

Marty

By mcianchette Date 04-23-2002 14:29

Thanks for your rapid reply. I am not sure, however, about the volume changes. What is the recommended volume change and why is this variable? I assume that this is simply to ensure a more complete purge with a "5" volume change than, let's say, a "2" volume change. Could you provide insight? Thanks.

By MBSims

Date 04-23-2002 21:30

Your assumption is correct. 5 or 6 volume changes is a typical practice in the piping industry and is recommended in AWS D10.11, Recommended Practices for Root Pass Welding of Pipe without Backing. The idea is to reduce the oxygen level inside the pipe to a point where little or no oxidation of the root pass occurs. Instead of waiting for the time required for 5 or 6 volume changes, this could also be checked with an oxygen analyzer at the purge gas exit point. We look for oxygen content to be <2% prior to welding.

Marty