Changing Shielding Gas for FCAW

Date 09-24-2009 18:46

Hello Chris, you can certainly go with wires that can be run with a straight Co2 as a shielding gas, as you mentioned yourself, you just need to be mindful of the CVN values and also the manufacturers recommendations for their particular wire. Some wires are specified to be run with the straight Co2, others specify either Co2 or 75Ar/25Co2, still others are specified for use with 75Ar/25Co2 exclusively. There are yet other wires that allow for Argon up to 90 percent with a balance of Co2. Just be sure to check the CVN values as they apply to your specific application. You likely have yourself covered pretty well. Best regard, Allan

By eekpod

Date 09-25-2009 10:16 Edited 09-25-2009 10:19

Thanks Allen,
Yes in fact the Lincoln wire that we use is rated for either straight CO2 or a mix of Argon/ CO2. Besides the CVN I wanted to make sure there wasn't anything else I was missing before I suggested if they go ahead and make this switch.
For instance, we got our Bridge fabricator certification 3 months ago, but when I ran our bridge PQR test plates we used the mixed gas, now if I change to straight CO2, I believe they are no longer covered under the old WPS, so I'd have to run new PQR test plates, and that wasn't cheap.
I am going through the bridge code now and the seismic code as well, hopefully by the end of today I'll have an answer.
Thanks
Chris

By waccobird (****)

Date 09-25-2009 12:24

Hey EEK working to D 1.5 is a pain $$ after getting used to D1.1. PQR's run @ 1500.00 around here for testing including charpy's. Yes you will have to qualify the wps for the gas change. I feel 75/25 is worth the minute price difference, it welds cleaner, easier, and allows for the ability to have more versatility in Production positions. Plus when I was developing our FCAW PQR I feel the results were better utilizing the 75/25. Just my opinions

By eekpod

Date 09-25-2009 18:25

Ok here's what Iv'e come up with so far;

D1.1 Table 4.5 (19) Since I'm changing from a mixed gas to a single gas, #19 applies because I am changing the specified nominal percentage composition. But all that means is I need to write new WPS's with the single gas but I'm still pre-qualified either way.

D1.8 Seismic not applicable, doesn't mention gas composition.

D1.5 5.13 takes me to Table 5.3. Surprisenly gas composition is not an essential variable so my intrepetation is that I can change it and not have to re qualify my PQR's. I do find that strange, hope I'm not missing something.

thought just came in, do I have to re-certify my welders with the new gas?
Chris

By waccobird (****)

Date 09-25-2009 19:01

I would say no you don't have to but the code talks of the welders familiarity with the tasks assigned, base metal etc.. You Qualify a welder to a process, position and thickness.
After reading your repost and checking your thought direction It looks like a change in gas is not a reason for a new PQR you should be able to write the WPS with the gas change. I'd think the gas should be an essential variable but after reading the clauses and tables I would tend to agree with your thoughts I put down the AWS 1.5 :2002 in 2003 and have been spoiled with D1.1. and need to open it more often Thanks EEK

By eekpod

Date 09-28-2009 10:17

Thanks for your thoughts. Chris

By Metarinka (****)

Date 09-30-2009 22:30

on the practical side, is the wire your using compatible with 100% c02? and will it produce acceptable welds at the same deposition rate with similar technique? I.E is this an easy transition?

at one job I did a large time study and cost evaluation of all wire feed welding for a shop. Off the top of my head gas usage accounts for less than about 2% of overall welding costs. So little in fact that 100% of the time a more expensive gas was choosen if it showed: a lower defect rate, a mild increase in deposition rate, or had a larger parameter range or was just plain easier to use. It's very easy to get focused on the consumables cost of welding which is overall about 5-30% of total welding cost, and not realize that a relatively small savings such as changing shielding gas, creates a bigger expense such as increased defect rate.

The old phrase " Penny wise, dollar foolish" comes to mind

Then again my knowledge of FCAW details is weak; if I remember correctly, 100% CO2 gases generally give good penetration and bead characteristics, albeit with more spatter.

just the ramblings of a madman....

By TimGary (****)

Date 10-01-2009 10:34

Metarinka is correct.
I suggest you do some testing first.
I believe you'll find that you'll lose three times the money saved by switching gasses, in labor cost, directly related to cleaning excess spatter and repairing LOF defects.

Tim

By eekpod

Date 10-01-2009 13:19

The wire can be used with both 100% and mixed, I checked that before I even started.
I spoke to some of our welders and they have never tried it with the 100% and the salesman who supplies of this product told me it will produce more smoke, and the appearance will change a little, not quite as "flat" of a look, it will have more of a ripple to the weld.

We will be trying this out before we make the big switch, I was just doing my homework on all the other aspects of it. Thanks Chris