Ar purge for Low Alloy steel

[qaqcmpm]

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?

[Natarajan Devan]

Dear

Clint specification is the first requirements of the application, even though in general

GTAW cr-mo, Purging root weld quality will   be    achieve  uniform very smooth counter penetration,

 regards

N.Devan
 

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Natarajan.Devan
Senior Welding Inspector
Al Furat Petroleum Co-Syria
Syria Shell Petroleum Development
Tel: 00963 11 6182103 Res
Mobile: 00963 933052385

INDIA: 0091 9840330143 Res.
Mobile: 0091 9884745254

[Yadav Shiva]

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

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[Chandra, Vasanthan (Lagos)]

To avoid oxidation especially for Cr-Mo steels.

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[Rui....@pt.linde-gas.com]

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....@pt.linde-gas.com, www.linde.pt

Yadav Shiva <luvsh...@gmail.com> Sent by: material...@googlegroups.com 15-04-2010 07:54 Please respond to material...@googlegroups.com

To material...@googlegroups.com cc Subject Re: [MW:4846] Ar purge for Low Alloy steel

[ravishankar menon]

Dear all,

Usually purging is necessry to eliminate presence of oxygen while doing low alloy steels and SS materials,To eliminate oxides inside the pipe weld beads, Cofirm purging should  be with nitrogen  and mixture of hydrogen and nitrogen or organ well before the welding  to remove oxygen in side the pipe.

 

Ravishanker, 

---

From: qaqcmpm <mamuj...@gmail.com>
To: Materials & Welding <material...@googlegroups.com>
Sent: Thu, 15 April, 2010 11:27:58 AM
Subject: [MW:4843] Ar purge for Low Alloy steel

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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[Amir Zakee Adnal]

Please bear in mind certain client spec calls for a limit the presence
of oxygen in the purge dam, therefore the purity of argon use for
purging is important. If the spec calls for 500 ppm of oxygen you need
to use 99.999% of argon.
The purpose of purging is to eliminate the oxidization of root bead
from inside thus to maintain the corrosion resistance of the welding.
Please take note also on the spec requirement of the removal of the
purge whether the purge can be removed after certain passes.

[kannayeram gnanapandithan]

For Cr>3%, it is always better go for purging, if customer insist for all low alloy, pl do it because it will better and uniform root penetration

KGP

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[Ahmed Eissa]

dear all according to API 582 CLAUSE 7.3 see the following   "Back purging is required for the GTAW and GMAW processes for welding materials having a nominal chromium content greater than 2l/4% unless the joint is ground or back gouged to sound metal." the cause  is "back purging gas is selected to prevent oxidation or scale formation on the underside of the weld" --- On Mon, 4/19/10, kannayeram gnanapandithan <kgpan...@gmail.com> wrote: