Purge gas is normally stopped after root and hot pass .
Purge gas is required to ensure that root pass is not oxidised during deposition of fill and cap pass.
Root can get oxidised only when it gets red hot during fill and cap pass.
If thickness of root and hot pass is sufficient then chances of root getting oxidised is less.Normally your PQR will establish this thickness.
However,for thin wall piping where root,hot and cap are only three passes(meaning no fill passes or if material is highly reactive),it is better to continue gas purging.
For thicker pipes one can stop puging after root and hot.I am based in abu dhabi and you may call me to discuss this issue further.
Cheers.
Regards.
Ashwani Kumar Khare
(M) +971 50 9258963
Post Box 303,Major Projects Division,
ADMA OPCO,Abu Dhabi,UAE
http://www.linkedin.com/in/ashwanikumarkhare
To: materials-welding@googlegroups.com
Subject: [MW:7587] Purge Gas
Date: Sat, 16 Oct 2010 09:14:09 +0400
From: jhardcastle@euromechanical.com
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 Emirates |
| Phone: +971 2 550 08 99 |
| Fax: +971 2 5501898 |
| Mobile: +971 50 4445873 |
| Email: jhardcastle@euromechanical.com |
| www.euromechanical.com |
| |
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