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[MW:10026] MW:10003- Nitrogen Purging for SB 409 Alloy 800H

By Materials & Welding
Hello, Mr.. Rao & Praveen Alavander,
 
There are conflicting arguments on the use of Nitrogen alone  as backing gas for austenitc stainless steels and Nickel alloys.Nitrogen is quite popular as a mixed gas  with Argon. The pros of nitrogen is it's relative less expensive compared to other shielding gases, cons chances for undesirable  phases, brittle phases like nitrides. ASME Sec-IX does not insist change of backing gas as an essential variable, hence fabricators do not have any mandatory requirement of procedure  re-qualification.
 
Perhaps a good way would be would be to micro structural evaluation on the root of single sided welds to check for any hard , brittle phases. Micro-hardness check from the root  to at least 1/4" to the top ad the corrosion tests (if required) in addition to ASME Sec-IX qualification tests.
 
Appreciate if you could circulate the observations as convenient. Some clients are very  specific on use of Nitrogen Backing ( see below the hyperlink).
 
The attached article is quite interesting on the effects of various types shielding gases for welding. The highlighted texts are on the effects of nitrogen.
 
Thanks.
 
 
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario,Canada.
Email-pgoswami@sympatico.ca,
 
  1. http://www.oilfieldtrash.com/custom/php/files/1260853475AESW010%20Welding%20Requirements.pdf---- Clause 11.14.4
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of praveen alavandar
Sent: Thursday, February 24, 2011 12:25 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:10003] Nitrogen Purging for SB 409 Alloy 800H


Dear Rao,
 
One thing for sure is Nitrogen is used as a purging gas for welding duplex/super duplex stainless steels.
 
Nitrogen is nonflammable and does not support combustion and is slightly lighter than air.
Nitrogen is inert except at arc welding temperatures where it will react with some materials like Aluminium, Magnesium and Titanium.
 
Personally I have not tried on Nickel based alloys but you can give a try. I dont see any harm to weld a test coupon, check for mechanical and corrosion properties if its come out to be ok, you can use it on you job.
 
As regards nitrogen purity, the AWS A5.32 Specification for Welding Shielding Gases specifies minimum nitrogen purity of 99.9% and maximum dew point of the gas as -51 Deg.C. The AWS classification for this gas is SG-N. This AWS A5.32 is for shielding gas, how ever you can take it as a guidance for selecting your purging gas.
 
Excess nitrogen in the order of 5% and above in the shielding gas (usually with Argon) can erode the tungsten electrode.
 
If you purge with nitrogen and an open root there should be no issue of nitrogen contamination of the tungsten electrode provided the purging pressure is not excessive.
The argon flow from the GTAW torch as shielding gas will protect the tungsten electrode.
 
Regards,
 
Praveen Alavandar
 
 

--- On Wed, 2/23/11, P.Rao <vasantharao2009@rediffmail.com> wrote:

From: P.Rao <vasantharao2009@rediffmail.com>
Subject: [MW:9985] Nitrogen Purging for SB 409 Alloy 800H
To: materials-welding@googlegroups.com
Date: Wednesday, February 23, 2011, 5:06 PM


Dear All,

Can i use nitrogen Purging for GTAW Welding of subject material.

Are there any consumables available with Flux cored type?

I have a requirement to weld subject material from single side with ERNiCr-3 wire + ENiCrFe-2 electrodes. Single side only accessible.

Pl. provide your values inputs.

P.Rao

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