Re: FW: Re: [MW:29172] RE: 28982] Backing gas as per API RP 582

Many times I have seen that even some of out best engineers still argue about this issue...

In root side of a single-side weld, the slag in SMAW or FCAW only protects the weld and not areas adjacent to weld (i.e. HAZ and heat tint area in Stainless steels). Slag does not protect Root HAZ and heat tint area in Stainless steels; 

Welding is not only about the "weld metal", 

A welding engineer must consider HAZ as a part of the weldment... 

This is as basic as it gets, whether you are dealing with SMAW or any other process.

Heat tint area consists of a layer between 50-300 microns (depending on temperature) which is a result of Chromium depletion of the underlying surface. Sometimes this Cr-depletion is so severe that the the Chromium content drops below minimum level and respectively, the corrosion resistance of these layers under heat-tint film drops way below minimum requirements. It will create corrosion initiation sites which is the most critical and time consuming stage in corrosion...

Are we OK with creating and leaving in place highly-stressed corrosion initiation sites at every welded joint in our system...?

And turn a blind eye on such an important issue...?

Do we really want to loose corrosion resistance If we are using stainless steel for its corrosion resistance characteristics...? 

Of course not... 

This means to ruin corrosion resistance of the welded joint, why would we do that...?

We don't downplay these issues, We take care of them...

It is not a good idea to go against the design and jeopardize the corrosion resistance of all your weldments. 

As a welding engineer, it is our duty to take care of such detrimental effects of welding by preventing them from happening or come up with a remedial action...

 

To conclude, if your material, especially stainless steels, is used for its corrosion resistance characteristics, and heat of welding reduces its corrosion resistance (which it normally does), it is highly recommend to apply back purging, otherwise make sure to remove the oxide layer by grinding, blasting or chemical cleaning methods (i.e. pickling). 

But in cases where stainless steel is not used for its corrosion resistance (e.g. non-corrosive cryogenic applications), the above mentioned protection or oxide removal may not be required (although it will always be beneficial).

Please Remember, if you are using welding processes other than SMAW/FCAW, back purging shall be done to protect weld metal, which obviously, it will also protect areas adjacent to the weld. Furthermore, one might ask "why no one talks about the HAZ or heat-tint area of welds on the outside of the pipe or vessel?" The answer is, because the outside surface is not in contact with the process fluid but for inside surface, it is totally different. I think everyone agrees on this one. Of course, in many cases, the pickling and/or passivation of outside surface is a requirement which is the subject of another discussion.

 

Regards

Ramin  Kondori

Sr. QA/QC & Welding Engineer

-----------------------------------------------------------

PG-Dip. in Welding Engineering (IWE  AT  0070)

BSc. in Civil Engineering (IUT)

BGAS Painting Inspector

ASNT Level I&II

                        

On Thu, Feb 28, 2019 at 7:15 AM PGoswami <pgoswami@quickclic.net> wrote:

Monoj,

 

Please see the extract from API-RP-582, which states clearly that purging is a must for GTAW &GMAW process when Cr-in the steel exceeds 2.25%. SMAW welds NEVER require any purging. Purging usually is the practice for open root welds, where the root requires protection from oxidation, when Chromium is above that specified amount. SMAW welds never require purging as the slag acts to protect the root. That's the very basics of SMAW welding process , where slag metal reaction  and separation is the key.

 

For fillet welds of thicknesses specified below "Heat Tinting "  is a possibility. Use of purging gas could  help to avoid oxidation and heat tinting for the thickness(2-5mm) as  mentioned here. However note use of small diameter (2.4mm) could be useful to avoid heat tinting if the thickness of the component being welded is around 5mm.

 

Minor heat tints are removable by acid pickling. Depending on the corrosivity of the process media, many clients does insist on this method. In the attached  document you'll find some examples of heat tint depending on the  "Oxygen" content on the root. For many fillet welds it's not possible to purge, however controlling heat input helps to avoid heat tint. In another word adoption of correct welding practice is essential.

 

Thanks,

 

P.Goswami.P.Eng, IWE.

Independent Welding & Metallurgical Specialist

Linkedin: https://www.linkedin.com/in/pradip-goswami-2999855/

Email:pgoswami@quickclic.net,pradip.goswami@gmail.com

Whatsapp:1-905-9793232

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of muneebslsa@gmail.com
Sent: February 27, 2019 3:03 AM
To: materials-weldingmaterials-welding <materials-welding@googlegroups.com>
Subject: Re: Re: [MW:29161] RE: 28982] Backing gas as per API RP 582

 

You can check the attachments, but anyhow when it comes to thinner membrane regardless of whatever the consequences might be the case for oxidation which is non occurrence when we simply imagine for fillet welds but anyhow socket welds aren't with this case of lap to lap fillets, hence a detailed study of amendment to be incorporate with through and through case studies and failure analysis stipulating clauses shall be ensured in international standards.

 

Anyhow now the case as per the research is chromium depletion (causing heat tints / discoloration) for thinner membranes especially for fillets, So to be conclude that there should be some detailed studies as per AWS D18.2 / NORSOK STANDARD M-601 especially for fillet welds.

 

At any cost don't accept the requirement unless owner is providing his clause which is already stipulated in owner's manual or international standards, the research i have ensured is from my previous owner requirement which i did not agree and the international standards which I have quoted is for open root / butt welds.

 

Thanks.

 

---

Regards,

MOHAMED MUNEEB MAHABOOB

 

 

From: sandeep kumar

Date: 2019-02-24 11:20

To: Materials & Welding

Subject: Re: [MW:29146] RE: 28982] Backing gas as per API RP 582

To be specific, as you know purging purpose in SS is mainly for shield against oxidation which took place when molten metal kiss the oxygen from atmosphere. Now when you welding a fillet weld the amount of oxidation is corresponding to the amount of heat supplied vs. encounter of molten weld metal to the atmosphere without shielding. 

 

A fillet weld having a configuration without any gap and zero flow of molten metal to the back side will defiantly not require any purging. Its recommended to use a optimized low heat input. I advise you although to put gas backing upto 2 mm thickness as the low heat dissipation in SS can melt through thickness during welding.

 

Thanks & regards

Sandeep Kumar

On Friday, February 22, 2019 at 6:19:06 AM UTC+3, John Manoj wrote:

Thanks for the reply, Is back purging is required when we do fillet welding on a thin (2mm to 5mm) SS base material, for example some cleat welding or pad welding or socket welding with GTAW or SMAW process.

 

Expecting a reply.

Thanks,

Manoj

 

Dear Mr. Goswami,

 

In 2016 editions of API RP 582 the purging gas requirement given in subcluases (a) (b) (c) but in previous editions purging requirement given in clause 

 

On Mon, Jan 28, 2019 at 9:53 AM PGoswami <pgos...@quickclic.net> wrote:

Manoj,

 

SMAW never requires back purging. It's the "slag" generated by the process, which protects the weld root. This is just back to basic scenario.

Thanks.

 

P.Goswami.P.Eng, IWE.

Independent Welding & Metallurgical Specialist

Saudi Aramco: Designated Project Welding Engineer(DPWR)& Quality Management Personnel

Linkedin: https://www.linkedin.com/in/pradip-goswami-2999855/

Email:p...@quickclic.net,pradip.goswami@gmail.com

From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Manoj John
Sent: January 27, 2019 8:04 PM
To: material...@googlegroups.com
Subject: [MW:28982] Backing gas as per API RP 582

 

Dear Experts,

 

As per clause 7.3 of API RP 582 Ed. 2016 back purging required for GTAW & GMAW process but no where I could found for other process like SMAW.  Is it mean that if we do welding with SMAW process back purging is not required?

 

Please share your interpretation.

 

Thanks and regards

 

Manoj.

 

 

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