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.
Kind Regards
Mahmoud Abdul Fattah
+971506827001
From: sujay kumar <sujay1199@gmail.com>
To: materials-welding@googlegroups.com
Sent: Sun, October 17, 2010 7:26:43 AM
Subject: Re: [MW:7602] Purge Gas
we can remove the purging once root and hot pass is compete,temperature of metal will not oxidised inside ,when welding is in progress.
sujay
+97507217119
On Sat, Oct 16, 2010 at 9:14 AM, John Hardcastle <jhardcastle@euromechanical.com> wrote:
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 Fabrication Manager
Euro Mechanical Contractors Company Factory P.O. Box 46153
Abu Dhabi
United Arab EmiratesPhone: +971 2 550 08 99 Fax: +971 2 5501898 Mobile: +971 50 4445873 Email: jhardcastle@euromechanical.com www.euromechanical.com
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