[MW:2455] Re: 2448] Re: requirement of purging in CS/SS pipes

Good suggestion John. Usually back purging is recommended for welding of P5 and above materials

On Tue, Jun 16, 2009 at 8:06 PM, John Henning <jhenning@deltak.com> wrote:

I suggest you try a small experiment and you will see quite quickly why argon shielding of the back side is recommended for stainless steel.  Take several pieces of stainless, thickness and exact size are irrelevant, and make two welds from on-side only; one weld with argon backing gas and one weld without an gas backing.  The one with backing gas will be bright shinny (maybe a small amount of heat tint depending on the quality of your back purge) with smooth, well formed ripples.  The one without backing gas will be highly irregular covered with a thick gray coating and individulal weld ripples will probably not be discernable.  Cross section both welds, polish them, and look at them under a microscope. You will see that the grayish material extends into the weld metal for at least several grains in depth.  The gray material is an oxide formed at high temperature and has a very high chromium content.  Without backing gas you have made a highly irregular surface, posoous with penetrations into the surface and removed from solution the alloy addition, chromium, which confers general corrosion resistance - to put it simply you just provided corrosion an ideal condition in which to initiate.  

 

While any weld will benefit from a back purge in prevention of oxidation, since stainless steels are typically used in more aggressive environments it is more important that they be back purged to prevent premature failure due to corrosion. 

 

Depending on application and customer, argon back purging will be recommended when the chromium content reaches around 2-1/4% or greater and will not be restricted just to stainless steels. 

 

john

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of prashant pansare
Sent: Tuesday, June 16, 2009 6:56 AM
To: materials-welding@googlegroups.com
Subject: [MW:2448] Re: requirement of purging in CS/SS pipes

OK,why  SS is more suseptable than CS to get oxidised? --- On Tue, 16/6/09, Antonio Ruscitto <ARUSCITT@metrogas.com.ar> wrote: From: Antonio Ruscitto <ARUSCITT@metrogas.com.ar> Subject: [MW:2447] requirement of purging in CS/SS pipes To: materials-welding@googlegroups.com Date: Tuesday, 16 June, 2009, 5:02 PM Hi: I think that is for the same reason. I´ve qualificated a Welding Procedure Specification with ASTM 106 G° B, with gas purging Ar inert gas. Because that reason   Regards Antonio >>> Sukamal Naskar <sukamalbecmet@gmail.com> 11/06/2009 08:36 pm >>> For Stainless steel we do purging ( Inert gas like Argon ) to avoid the oxidation at the root. Stainless steel is more susseptable to oxidation than carbon steel. for carbon steel root is not so much suseptable to oxidation , hence we don't use purging gas like Argon.   Regards,   On 6/11/09, prashant pansare <prashantpan_99@yahoo.co.in> wrote: 1) Why purging reqd.while welding with E316 / 316L for SS  pipes? 2) Why purging not reqd.while welding with ER 70-S for CS  pipes? Pl. reply. Bring your gang together. Do your thing. Find your favourite Yahoo! Group. -- Sukamal Naskar Malaysia ********************************************************************* ¡IMPORTANTE! Para evitar accidentes por inhalación de monóxido de carbono: - Mantenga los ambientes ventilados en forma permanente. - Revise que la llama sea color azul y uniforme. - Instale y haga revisar periódicamente sus artefactos sólo a través de gasistas matriculados. Recuerde que los artefactos a gas pueden emitir Monóxido de Carbono: un gas altamente tóxico e imperceptible. Más consejos en http://www.metrogas.com.ar ********************************************************************* Este mensaje es privado y confidencial y va dirigido sólo al destinatario indicado. Si lo ha recibido por error, por favor avísenos inmediatamente vía e-mail a error-mail@metrogas.com.ar y tenga la amabilidad de eliminarlo de su sistema.. La utilización o divulgación de su contenido puede importar la comisión de un delito. No copie, reproduzca o divulgue -en forma parcial o total- su contenido. Cualquier opinión contenida, es exclusiva de su autor y no representa la opinión de MetroGAS S.A. - Muchas gracias. This message is private and confidential and it is only intended for the addressee named above. If you have received this message and it is not addressed to you, please advise us immediately at error-mail@metrogas.com.ar and kindly remove it from your system. The use or disclosure of its contents may be regarded as an offense. Do not copy, reproduce or disclose them, either partially or fully. Opinions are the exclusive responsibility of the author and do not represent the opinion of MetroGAS S.A. - Thank you. :: http://www.metrogas.com.ar   Bollywood news, movie reviews, film trailers and more! Click here.

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