Hi John,
I don’t know what code you are working to, the material you are welding or dimensions of your job. However, in general inert gas protection is required until the local material cools below a certain temperature (e.g. 300-450°C depending on the material) to prevent oxidation and thereby ensure the corrosion resistance at the joint is as good as the base metal. Practically this means that even though the root run is complete, additional passes will heat the root material above this temperature (unless the pipe is very thick) such that this region requires inert gas protection.
Hope that helps
Andrew Short, MeltTools Ltd.
T: +64 9 6222758
M: +64 220134194
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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of John Hardcastle
Sent: 16 October 2010 18:14
To: materials-welding@googlegroups.com
Subject: [MW:7587] Purge Gas
When can we remove backing gas purge from non-ferrous pipe joints.
Can we remove the gas purge once the root run is complete, or once the root and first hot pass is complete.
We leave the gas purge on until the joint is capped and i am sure this is wasting gas.
John Hardcastle |
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Fabrication Manager |
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Euro Mechanical Contractors Company Factory |
P.O. Box 46153 |
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Phone: +971 2 550 08 99 |
Fax: +971 2 5501898 |
Mobile: +971 50 4445873 |
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Email: jhardcastle@euromechanical.com |
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