Prostar FC 71C Gas Mix mistake.

Date 01-26-2010 22:14

Greetings,

The shop has a welding procedure specification for E71T-1C.

The procedure shows a sheilding gas of 100% CO2.

The welder hooked up the wrong sheilding gas and used 80% argon 20% CO2 and welded most of the day.

He has welded out an entire HSS 4 x 4 X 1/4 structural frame.

The manufactor recommends 100% CO2. I am wondering if the gas mix will damage the weld quality?

Any suggestions on how to fix this problem??

Thanks David

By ssbn727 (*****)

Date 01-27-2010 00:55

This is something that needs to be kicked up to the EOR (Engineer Of Record) in order to make the decision of whether or not to accept the work as is, or to agree with what most welding inspectors may decide that the WPS was not adhered to, and therefore they would not accept the work which would result in re-work... So kick it back up to the EOR and let them (Him or Her!;) ) decide this one!!! :) :) :) Besides, Allan explained some important factors that should be brought to the attention of the EOR and that's why they get paid the big bucks!!! :) :) :) Just my thought!

Respectfully,
Henry

By A_DAB_will_do (*)

Date 01-27-2010 14:37

David,

E71-T1C is the code for a 100% CO2 shielding gas wire. I did a quick search on line and couldn't find a ProStar product that had this AWS designation. Here's the catalog I did find.

http://ecatalog.praxair.com/wcsstore/prostar_eflyer_store/pdf/P-8469ATubularWire.pdf

They list a Pro star E71-TM, which is a 75/25 mixed gas product.

All that said, some of these E71 FCAW-G products can be used with either 100% CO2 or 75/25 Ar/CO2. Suggest you find a manufacturer's datasheet for your specific product. I'll second the recommendation that another poster made that you speak with the EOR. Shielding gas will alter the mechanical properties of the finished welds. Based on what I saw looking at similar Hobart product datasheets, it' appears that the tensile properties of the weld go up and the impact properties go down when you switch from 100% CO2 to mixed shielding gas. Your EOR may reject what was done on that basis, or because your welder isn't qualified on that process with the mixed shielding gas. Or just because he's having a bad day. Regardless, good luck.

By aevald

Date 01-26-2010 23:33

Hello David, it is likely that you will receive two kinds of answers to your question. Many will likely tell you that you have nothing to fear and possibly rightfully so. Personally, I take a slightly different stance. Tubular flux-cored gas shielded electrodes(commonly referred to as dual-shield) contain fluxes that work as arc stabilizers, bead formers, alloying agents, and a host of other things. My understanding has been that the use of various shielding gases is allowed for by matching the shielding gas with the particular flux composition. A flux formulation designed to be used with 100% CO2 allows for a certain "loss/burn-out" of these agents while the welding is taking place. If an overly high amount of argon is present in the shielding gas some of the known burn-out or reactivity doesn't take place and can lead to possible crack issues or other metallurgical issues because of the change in the as-welded condition of the weld deposit. Tensile testing or other forms of destructive tests will be the only way that you could truly prove or disprove this line of thinking. Low temperature failure might result in some instances or other types of conditional failures that might not otherwise be an issue depending upon the service/purpose of the structure. This sort of thing has been discussed on the forum before and I really don't remember if it was every really resolved one way or the other. Just my $.02 for your consideration. Best regards, Allan

By eekpod

Date 01-27-2010 11:18

We use Lincoln Elite E71T-1 and it can be used w/ either straight CO2 or a blend. We use the blend 75/25 w/ out any problems for years.
Chris
PS both gases are prequalified

By js55

Date 01-27-2010 18:08

Is this an impact testing procedure?
And of course mechanical properties will change. Mechanical propeties will change with a lot of variations. Mechanical properties can change using the same exact everything on multiple specimens. But changing mechanical properties is NOT, and never has been, the issue of concern. The issue of concern is will a change lead to the weldment being rendered as non compliant with mechanical minimums, or code requirments, or customer specifications. And as the conformance data shows this is not the case for mechanical mins. The code and the WPS have been violated however.
Generate an NCR, get the customer rep/EOR to approve the disposition, re-write the WPS with the gas change, get the EOR to approve it and move on.
The good news is, your system worked. You caught the problem. The remedy does not have to be that painful.

By david bean (**)

Date 01-27-2010 20:48

It think it might be cheaper to qualify this procedure rather than rework all the welds.

I am going to run a test plate to establish a PQR and go from there.

Thanks for the feedback