Hi
Please see the attach:
Best regards
Rui Fernandes Pinho
Divisão de Gases Industriais
Desenvolvimento de Aplicação de Gases
Linde Sogás, Lda.
Travessa Joaquim Dias Salgueiro, Nº 44
4470-416 Vila Nova da Telha, Portugal
Phone + 351 22 999 8380, Fax: + 351 22 996 4039
Mobile + 351 91 473 9197
rui.pinho@pt.linde-gas.com, www.linde.pt
| Yadav Shiva <luvshiv2002@gmail.com> Sent by: materials-welding@googlegroups.com 15-04-2010 07:54
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Dear mamujabeli,
A backup gas purge is used for materials that are sensitive to contamination from air on single welded joints that are not backgouged (e.g. piping and closing seams). Backup gas is needed for certain chrome-moly steels (³3% chromium). A gas purge is not necessary for welding carbon steel or low alloy steels containing less than 3% chromium. Either argon or helium can be used for purge gas.
The best results for stainless steels and high nickel alloys are obtained when they are purged to oxygen levels of less than 1%. Purging with four to ten times the required volume is needed to obtain the relatively inert atmosphere. Where uncer- tainty exists regarding the adequacy of the purge, a mine safety oxygen analyzer can be used to check the oxygen level in the purge gas being exhausted from the weld area.
Initial gas purging is usually done at a high flow rate (e.g. 30 to 90 CFH) to flush the system, then reduced to a low flow rate (about 5 to 8 CFH) for welding. Particular care should be taken to ensure that the backup gas pressure is not excessive when welding the root pass, otherwise weld blow out or root concavity can occur. Adequate venting or exhaust is important to prevent excessive pressure buildup during welding. The area of the vents for exhausting backup gas should be at least equal the area of the opening used to admit the backup gas to the system. After completion of the root and several fill layers, the backup gas purge can be discon- tinued. The number of fill layers required before discontinuing the gas purge will depend upon layer thickness and penetration.
Yadav Shiva Chelliya,
Inspection Engineer,
Doha Qatar,
+974-6166465
On Thu, Apr 15, 2010 at 8:57 AM, qaqcmpm <mamujeebali@gmail.com> wrote:
One of our client specn asks for argon purging of root pass (pressure
retaining welds) for GTAW for Low alloy Cr-Mo steel? why it is
required any idea?
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