requirement of purging in CS/SS pipes

[prashant pansare]

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.

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[tong tong]

Back purging is required for the GTAW and GMAW processes for welding materials having a nominal chromium content greater than 2 1/4% unless the joint is ground or back gouged to sound metal. The purpose is to prevent oxidation or scale formation on the underside of the weld, the purge shall be maintained until at least 1/4 in. (6.3 mm) depth of weld metal has been deposited

[Sukamal Naskar]

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,

 

--
Sukamal Naskar
Malaysia

[Antonio Ruscitto]

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 <sukama...@gmail.com> 11/06/2009 08:36 pm >>>

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[prashant pansare]

OK,why  SS is more suseptable than CS to get oxidised? --- On Tue, 16/6/09, Antonio Ruscitto <ARUS...@metrogas.com.ar> wrote:

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[PREM SHANKARDUTT NAUTIYAL]

Hi

1) SS contains more than 11% Cr which has higher affinity to oxygen and to get oxidised and form Chromium oxide as compared to CS. Hence while welding SS materials it is always essential to purge with Ar for the root & hot pass to avoid oxidation at root.Argon purging at the root drives out all the entrapped Oxygen thus creating an inert atmosphere.

2) Now when you weld CS,generally no Ar purging is required.
However if you are fabricating a Nuclear Class 1 component, Ar purging is required for TIG and is an essential variable in the WPS even for CS welding.
You will definately find a difference in the root when you purge with Argon -- A good uniform penetration, free of oxidation.
Thus if you need a quality weld there is no harm in Argon purging for CS material . of course the cost will go up !

Regards

Prem Nautiyal
Godrej,Mumbai

On Tue, 16 Jun 2009 17:37:09 +0530 wrote

>OK,why  SS is more suseptable than CS to get oxidised?
>

>--- On Tue, 16/6/09, Antonio Ruscitto wrote:

>
>
>From: Antonio Ruscitto
>Subject: [MW:2447] requirement of purging in CS/SS pipes
>To: material...@googlegroups.com
>Date: Tuesday, 16 June, 2009, 5:02 PM
>
>
>
>Hi:

>I think that is for the same reason. Ive qualificated a Welding Procedure Specification with ASTM 106 G B, with gas purging Ar inert gas. Because that reason
>
>Regards
>Antonio
>
>>>> Sukamal Naskar 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 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 inhalacin de monxido de carbono:

>- Mantenga los ambientes ventilados en forma permanente.
>- Revise que la llama sea color azul y uniforme.

>- Instale y haga revisar peridicamente sus artefactos slo a travs de gasistas matriculados.
>Recuerde que los artefactos a gas pueden emitir Monxido de Carbono: un gas altamente txico e imperceptible.
>Ms consejos en http://www.metrogas.com.ar
>*********************************************************************
>Este mensaje es privado y confidencial y va dirigido slo al destinatario indicado. Si lo ha recibido por error, por favor avsenos inmediatamente va e-mail a error...@metrogas.com.ar y tenga la amabilidad de eliminarlo de su sistema. La utilizacin o divulgacin de su contenido puede importar la comisin de un delito. No copie, reproduzca o divulgue -en forma parcial o total- su contenido. Cualquier opinin contenida, es exclusiva de su autor y no representa la opinin 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...@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
>
>
>
>
>

>      Explore and discover exciting holidays and getaways with Yahoo! India Travel http://in.travel.yahoo.com/
>>
>

PREM S NAUTIYAL

CELL : 9820313278

[John Henning]

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

---

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

[Sreejith.Nair]

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

--
- Sreejith Nair-