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Up Topic Welding Industry / Technical Discussions / SMAW Cladding using ALLOY 625
- - By Stephan (***) Date 10-05-2008 16:08
Friends,

I have a question for you and I'm hoping very much that some of you experts may find a bit time to respond.

The question deals with the use of SMAW in the field of overlay welding in particular with "Cladding".

I mean to know that Shielded Metal Arc Welding is also nowadays an often used process to clad in particular interior bores of large flow control valves etc.

Since here very often Ni-Base Alloys as e.g. ALLOY 625 (AWS ER NiCrMo3) are used as the specific filler compositions and the efficiency in overlay welding is greatly influenced by the weld deposition rate I can remember well that it was greatly surprising me that SMAW - as a rather low efficient process - is nonetheless often used. I guess it might refer to the process universality itself that it's applied in this field.

However, my question is now:

"Does anybody of you fellows eventually use SMAW for cladding under the particular use of ALLOY 625 and furthermore - which were very interesting to know - what are the common or even maximum electrode diameters used?"

As well it were interesting to know how to meet the often severe requirements for low dilution when using manual SMAW. I guess therefore two layers were rather being welded instead of just one layer. Am I right by thinking so or...?

I'm preparing a presentation at the moment and your answers - the more the better for approaching an adequate cross section from the daily practical experience - would build the fundament for an important part of this presentation.

As I know there is probably no other nation in the world (the home of the famous INCONEL Alloys :-)) having more experience with the "science" of overlay welding as the United States of America I am looking forward to get some (short) responses from you.

These, however, were greatly appreciated!

Thanks in advance and best regards to all of you,
Stephan
Parent - - By jon20013 (*****) Date 10-05-2008 21:24
Stephan, I've not used SMAW for cladding however can direct you to very useful information here: http://www.specialmetals.com/index.php

Special Metals is the leading USA expert for these materials.  You should find some good information on their website!
Parent - - By 803056 (*****) Date 10-05-2008 22:38
My limited experience with cladding has been to use GTAW.

That being said, we have used 625 for dissimilar joints between HY-80 and NiCu using GMAW. Very touchy and we used an Argon-Helium mix for the shielding gas.

The weld bead is sticky, gooey and flows like toothpaste.  In general, I wasn't impressed with the results.

Best regards - Al
Parent - - By js55 (*****) Date 10-06-2008 12:26
Stephen,
You really hit the problem on the bullseye with your 'two layer' statement. That is the problem with ovelaying with SMAW.
But the problem isn't so much the high dilution, which is generally 25% to 50% with SMAW, its the combination of high diluton with the chemistry you need to end up with.
If you're going to be competitive in this field you have to find ways to cut costs, and two layers with SMAW ain't the way.
SMAW is fine when no other process will do, as for example accessibility problems. But you have to be cognizant of your dilution and your resulting final chemistry. In which case you may need to bump up the alloy content. You also need to be cognizant of the type of corrosive service you intend. If oxidizing you may only need to bump up the Cr for example, (though you will have to communicate the possibilities with your customer), if reducing maybe the Ni or Mo.
The reason pulse GTAW (even non pulsed GTAW wil see diluton that is generally too high) and GMAW (which can achieve dilutions inthe range of 7% to 15%)are used is that you can get away with one layer with minimal alloy enhancement, even though depositions from these processes is low.
The other thing with SMAW is that its manual. And ridges  and crevices in overlay layers can be problematic for corrosive services. Especially if there is an abrasive element.
Parent - By Stephan (***) Date 10-06-2008 20:42
Jeff,

thanks a bunch for your excellent response - it is as I said once - I am truly blessed since some of the greatest have already replied on my humble post!

As you said, the final result is what matters.

If I have learned correctly, very often even this result is being measured .04" above the fusion line and has to be "tailored" depending to the later impact the part is being affected by.

Thus as far as I have seen SMAW is used where "(...) no other process will do, as for example accessibility problems."

The particular parts to be clad and of which I am talking about, are generally machined after the cladding operations, which can be an additional issue. Since the times needed for even those subsequent processes are quite hardly influenced by the clad layer's "surface quality". Even as you said, "... ridges and crevices..." are much more often recognizable with SMAW as e.g. with GTAW a/o GMAW. This again may raise the overall cost for the cladding process singinficantly which has to be considered when calculating the invest for the equipment. Not to speak of the - quite expensive - actually unneeded weld metal being deposited due to not having obtained the metallurgical purity (by the must of welding multiple layers to obtain the metallurgical composition).

Thus an appropriate cladding process or system respectively, has to make sure that it meets both the metallurgical requirements - which is crucial of course - as well as being capable to fulfil difficult applications with respect to accessability to the area to be clad, e.g. small interior bore diameters.

The remainder has to meet certainly economic aspects (deposition rate) as well. And even all these aspects I wondered are surely hardly to be met by even using SMAW. And as far as I found out the users are trying thus to replace SMAW by even trying to use GTAW or as far as even possible sophisticated GMAW.

The latter however, has still great problems to be accepted - as we have discussed this once already (Nuclear) - as an adequate substitution for GTAW. Nonetheless GMAW has made somewhat great progress in the recent past and both excellent metallurgical properties (dilution << 7... 15%) of the clad layer(s) and economical aspects can be met with high accuracy.

However, I have asked myself what the maximum SMAW electrode diameter possibly were. Since I have assumed they should be somewhat greater (to compress the low process efficiency) I mean to have found out that the maximum diameter of Alloy 625 stick electrodes may be stated at ~ 4.0 mm(?). Is this true?

I don't know... even though it were understandable under the consideration of the electrode's resistance heating at high welding currents. Even that was the main reason for my humble question if some of the forum members have eventually used or are still using Alloy 625 stick electrodes for cladding operations and may kindly share their experiences with this process. Just even as you, Al and Jon did that so kindly. :-)

However, thanks a lot again Jeff for your informative answer and my best regards,
Stephan
Parent - - By Stephan (***) Date 10-06-2008 19:48
Al,

thanks a lot my friend for having taken your precious time to reply.

Yes...

I believe totally in what you have stated.

The presentation I spoke about deals with even the special characteristics of different advanced welding processes, in particular GTAW and as an additional step ahead modern sophisticated GMAW processes.

Therefore you may imagine how surprised I was when I saw in practice that those particular alloys are even nowadays deposited by using SMAW Cladding.

Thanks again and best regards,
Stephan

P.S. Hope you're doing good in "Vivaaa Las Vegas!"
Parent - - By js55 (*****) Date 10-06-2008 20:46
Stephen,
Strip cladding (either SAW or ESW versions)is an even more advanced process than GTAW/GMAW autos. The dilution can be as low as 3% to 5% with good fusion (though to my knowledge not with the SAW version. The equipment has been improved considerably allowing insertion into smaller diameter pipe. I believe they can do 4" NPS now. The equipment is very expensive but the savings in time and alloy content make it worthwhile if your going to be doing a lot of this stuff.
The beads are indexed and the strip is fed longitudinal to the pipe and then twisted to allow a circumferential (preferred) layer.
Parent - By Stephan (***) Date 10-06-2008 21:17
Jeff,

cheers for that!

Yes! I agree entirely with you.

I have gathered loads of information to being able to compare all the actual sophisticated cladding processes in an appropriate way. You know, for finding out the particular benefits and drawbacks. 

RESW is surely a most impressive and effective process, absolutely no doubts on that.

But... in particular with even smaller interior bore diameters contained within larger complex parts (cross bores, bore to bore geometries, bores with different diameters in one part,...) RESW is still limited by both monetary invest and process controllability (arc submerged underneath the flux). In particular with strip dimensions > 60 x .5 mm additional control devices for a safe avoiding of arc deflections, which can result in severe issues (insufficient penetration, abnormal wetting angles,...). Another issue may be the restricted capability for out of position welds.

Nonetheless. As I said. I am 100% with you.

There are certainly no other processes available combining both efficiency (especially with larger areas to be clad) and metallurgical benefits (very low dilution rates) in a way as e.g. RESW and also SAW (strip).

Here these processes are surely unbeatable.

Nonetheless, I have listened to a very interesting presentation at the last IIW International Conference in Graz Austria coming from an Asian fellow that time.

And besides all the undoubted benefits RESW does have... hmmm... there are some quite tricky details to be considered when wanting to use the process properly. Although, this is surely the case with every other process as well.

By the way the dilution rates or data for SAW scatter between 10... 25% (strip) and 15... 30% (wire).

At least to the best of my knowledge... so please correct me when I'm wrong.

Thanks Jeff!

Regards,
Stephan
Parent - - By Stephan (***) Date 10-06-2008 19:37
Jon!

/ "You should find some good information on their website!" /

Wooow!

This is tremendous and makes me quite :-)!

Truly excellent!

Thanks a lot Jon!

Best regards,
Stephan
Parent - - By 803056 (*****) Date 10-07-2008 00:48
Stephan:

Chicago was better. Then again, it all depends on the company you keep and the company I had in Chicago was second to none!

Best regards - Al
Parent - By Stephan (***) Date 10-07-2008 19:45
Hi Al!

I guess Chicago must surely ever beat all others - at least for me as it was the show I had the privilege to meet you and Lawrence! :-)

Best to you!
Stephan

P.S. Please cross your fingers...
You know, the countdown is running... merciless. :-)
Up Topic Welding Industry / Technical Discussions / SMAW Cladding using ALLOY 625

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