Dear Mr.Pradip Goswami, Thanks for the article, it was informative. I think the reason behind restricting Nitrogen as a purging gas (ARAMCO standard) when welding austenitic stainless steels is probably due to the fact that it can react with the weld metal and hence reduce the ferrite level to dangeroulsy lower levels. But the gas - metal reactions are much faster/efficient when Nitrogen is included in the shielding gas rather than purging. I have extensively used forming gas (95% Nitrogen + 5% Hydrogen) to weld grade SS321 with good results, I have noticed this yellowish tint on the weld root, but it has never been a problem. Probably not much of a study has been done about this yellow tint as described in the article. I think we can expect the same yellow tint to form on the root when we weld alloy 800H which has Titanium in it. Most of the times we have this stigma to use Argon as purging gas and most client specifications also insist the same, I think its a little too conservative. With Regards, Praveen Alavandar
--- On Sun, 2/27/11, pgoswami <pgoswami@quickclic.net> wrote:
From: pgoswami <pgoswami@quickclic.net>
Subject: [MW:10026] MW:10003- Nitrogen Purging for SB 409 Alloy 800H
To: materials-welding@googlegroups.com
Date: Sunday, February 27, 2011, 10:31 AM
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. - http://www.oilfieldtrash.com/custom/php/files/1260853475AESW010%20Welding%20Requirements.pdf---- Clause 11.14.4
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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 -- To post to this group, send email to materials-welding@googlegroups.com To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com For more options, visit this group's bolg at http://materials-welding.blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
| -- To post to this group, send email to materials-welding@googlegroups.com To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com For more options, visit this group's bolg at http://materials-welding.blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents. -- To post to this group, send email to materials-welding@googlegroups.com To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com For more options, visit this group's bolg at http://materials-welding.blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
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http://materials-welding.blogspot.com/ The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
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