We are working with a customer who is trying to get his employees qualified to d1.1 limited thickness, all position. They are running downhill 3G and the 4G test plates with alot of lack of fusion and penetration problems. The welds look great, but when we cut and bend the test coupons most of them break in half (several of them you can see the grinding marks where they polished the bevel face prior to welding them -zero penetration). We are running around 18.5 to 22 volts / 200 to 250 amps /DCEP/ A-36/ 45 deg inc. /1/4 root/ 3/8 thk/ .045 Superarc L-50, ER70S-3 wire with 95% Argon, 5% co2 shielding gas. We have tried preheat up to 350 F. We cannot switch to a different shielding gas or weld uphill due to the fact that their qualifications would not be applicable. We are talking about 75 to 80 welders who are working at this and we are all getting frustrated. Any suggestions would be GREATLY appriciated
Hi ATS!
Preheating to 350F? Hmmm...
what base metal are you using and at what thickness?
What's your joint configuration?
What polarity are you using?
In other words, more details are needed to find your root cause to these failures.
You may ask Ed Craig @ http://www.weldreality.com
He has a section where you can describe your problem of course, in greater detail and I'm sure that he'll help you out.
Best of luck!!! Oh yeah, Happy Holidays to ALL!!!
Respectfully,
SSBN727 Run Silent... Run Deep!!!
we are using a-36 mild steel 3/8 thick
joint is a single v with a 3/8 backer 1/4 inch root opening with no land and a 45 degree included angle
polarity-dcep
"...18.5 to 22 volts..."
That's your main problem. At this voltage and with 95Ar/5CO2, you are running in short circuit transfer mode. This has very little penetration into the base metal on plate thicker than 1/4". This GMAW short circuit mode is also not accepted by D1.1 as being prequalified, so unless you qualify the procedure with tensiles, bends and RT your welder quals are not valid either. To get the penetration needed to pass bend tests in 3/8" plate in 3G and 4G, you've got to bump the voltage up to 22-24 volts at least and run the 3G uphill. Another problem will be to get all those welders to keep their arc volts up to stay out of short circuit mode after they pass the test. Once all those welds start failing under load at the customer's site, that may be the least of your problems.
Ok I have a little different opinion.
Short circuit transfer is not a bad choice
If we are talking about 3/8 A36 with a bevel for a D1 limited thickness qual exam in any position than short circuiting transfer is most likely going to be the choice.. unless you are not doing the exam open root. Spray transfer will qualify strictly in the flat or horizontal positions
Your gas selection is an expensive one. you could achieve the same result with 75/25 or even straight CO2.
Volts are not too low they are likely too high.. Start at 17 volts and listen.. your short circuiting should be a fast consistant crackle. if it is inconsistant or slow crackle than lower by 1/2 volt incraments. If your welders can feel the wire pushing back than the voltage is too low, increase by 1/2 volt. With the properties of the gas you selected at 18 volts your welders may be experiencing the lower range of globular transfer (when large droplets form on the end of the wire) and causing poor sidewall fusion and excessive spatter. (when parameters are good you ought to see little or no spatter)
When in the flat position try turning the inductance to maximum.
When in the vert position (up or down can qualify with good technique) set the inductance between midpoint and minimum
When overhead shortcircuiting set inductance at minimum value.
Check equipment.
Is your contact tip flush to 1/8 inch ouside your nozzle?
Are your welders focued on keeping a 3/8 inch stickout? Remenber, the difference between a 3/8 and 5/8 stickout in short circuit mode can be 25 to 35 amps (enough to provide lack of fusion)
Open root? what is your gap set at?
Root face for test plates? 1/16 inch is best for open root
Bevel angle? 70 degrees included angle is best.
Backing bar? is it flush? what is the gap?
Preheat? why? if your not going to pre heat during production than pre heat during quals defeats the purpose of the qual.
You're right - we do have different opinions. The application that was mentioned was AWS D1.1 (Structural Welding Code - Steel), limited thickness qualification. The thickness range would be 1/8" to 3/4" thickness. Having looked at a number of weld failures in structures welded with GMAW-SC, the results of welder qualification bend tests, and knowing that they wanted to qualify a good number of welders, I could not agree with choosing GMAW-SC for this application. While I agree that it is possible for some people to produce sound welds by careful tweaking of the settings, my experience has been that each welder will adjust the settings to their liking after they pass the test and the settings the welders like are not the settings that consistently produce sound welds. Short circuiting mode is not appropriate for structural welds in material greater than 1/4" thick. However, there are applications where short circuit mode is a good choice and I would have no problem using it. This particular case just isn't one of them.
Marty
In most instances I would agree with your assessment of how to join structures. However, the first sentence of the original post specifies "all position" qualification. I can't see qualification welds done overhead or V up in spray transfer. This is why I suggested Short circuiting parameters.
I agree - spray transfer is not going to be practical for their desire to have an all-position qualification. As I read the original post over again and saw the statement "We cannot switch to a different shielding gas or weld uphill due to the fact that their qualifications would not be applicable", it occurs to me this is an attempt to backfit welder qualifications for work already done. They seem to have discovered that the original welder procedure produces welds that may have acceptable appearance, but are not sound. To get deeper penetration, the CO2 in the shielding gas needs to be increased to 15% or greater and the current needs to be increased. You're suggestions are good ones for improving the qualification test results, but I can't see GMAW-SC providing consistently sound welds for this application.
By mas
Date 12-23-2004 13:57
Why 95/5? It appears you are trying to qualify welders using the wrong procedure.
It sounds like you may be in the short circuit transfer mode. This would explain the failures you found. Check your amperage and voltage using calibrated meters. Read the voltage as close to the arc as reasonably possible.
Newer GMAW equipment (Lincoln STT/Miller Axcess) may be helpful. I agree that Ed Craig is an excellent source to answer any GMAW questions.
For structural applications traditional short circuit should be avoided. The bend tests you now possess shows you why.
You can get much more current with this process downhill. The current you are running would work for vertical up.
The 95-5 will get you into spray transfer mode quicker than 75/25. The backing thickness of 3/8" is also providing a pretty big heat sink. The faster the welders travel downhill the more energy will be used to melt the base metal so don't try to carry much metal at all.
If this is trying to catch up with work that is already done, I would really question the quality of the work done. The WPS should provide adequate parameters for performing these welds. Is there a WPS ?
Have a good day.
Gerald Austin
http://www.weldinginspectionsvcs.com
Hi Guys,
Compliments of the season to you all from "Downunder"
Just thought I would add my 2 bits to the discussion regarding GMAW in the Vertical Down position. If you are looking to start a structural steel welding job using this process/position don't.
If you are looking to qualify guys after you have completed a project -best of luck.
I have spent 11 years as a Coded Welder, 12 years as a CWI with 4 of these years as a radiographer and I do not have one nice story to tell about GMAW unless you are welding very light gauge steel (boat trailers etc)After radiographing numerous welder qualification coupons the amount of lack of fusion (inter-run and sidewall) was unbelievable when the exterior of the weld looked perfectly acceptable.These failures were generally in the 1G position,the problem seemed to be either incorrect torch angle or more often than not trying to put too much metal in in one run.
This causes the molten pool to run ahead of your arc and stops the arc from directing the majority of the heat on to the run below.
This is exacerbated in Vertical Down as the molten pool is running downhill that fast that you have to be flying to keep ahead of it.
You get a good looking weld with no fusion underneath.The "pulsed migs" help to hold the metal from running but they are usually only used for open roots in pipes etc.
GMAW is a perfectly good process when used in the right application but in my opinion (and I stress this is only my opinion) GMAW, Vertical Down and Structural Steel Welding should not appear in the same sentence.
Regards,
Shane Feder
Welder qualification to D1.1 requires use of a written WPS. This can be either a prequalified WPS based on Section 3 or one that has been qualified according to Section 4. In the case of GMAW-S, because of the potential for lack of fusion, there is no prequalified WPS. Each WPS must be qualified. If you don't have a qualified WPS, stop right here. Everything you are doing is a waste of time. If you do have a qualified WPS, then someone must have been able to produce a sound weld that passed visual inspection, bend tests, tensile tests, etc. If so, other welders ought to be able to duplicate the feat. My first suggestion would be to get the welder who created that sound weld to show you how he did it.
Your parameters are in line with what Lincoln lists as typical for L-50. Preheat should not be necessary. IMHO 5% CO2 isn't going to do much for you. 75/25 or straight CO2 would have been a better choice. But, apparently, that is not an option here. It looks like an uphill progression for the vertical might have been a better choice. Going downhill will result in less penetration. But, again, apparently that is not an option here.
FWIW the problem of creating sound welds with GMAW-S is why most structural work is done with some other process. It is certainly possible to produce sound welds with GMAW-S. It does take proper training and practice. I know welders that can do 5G downhill welds on 3/8" material that will pass a bend test. I know a lot more that would have a real problem and might never be able to do it. And in this case, your customer has set you up with a situation requires higher than average skill.
What you have available to work with is the range of parameters in your WPS and welder technique. It appears you have tried everything within the range of your WPS, so that leaves welder technique like stickout, travel speed, gun angle, weave pattern, etc. It is hard to troubleshoot one welder remotely, much less 75 to 80. But I can repeat some of the basics that the welders should have already learned. The key to success when welding downhill is keeping the arc at or very near the leading edge of the molten pool. You have to move fast, but stop long enough at the edges to get fusion. Using stringer beads instead of a weave might help. That said, each welder is going to have to find a technique that works for him.
Frankly, it seems like your customer set you up to fail, maybe not on purpose, but fail nonetheless. I hope you can find a solution.
Arnold,
I have tried replying to your email 3 times and they have been blocked at your end for some reason.
Maybe contact your service provider and find out what is happening or you can ring me on (International Access code) + 61 + 408 502 700.
I think it is 15-21 hours time difference depending on your location.
Regards,
Shane Feder
Got to agree with Malcom.
A couple of things to keep in mind...
Short arc is not prequalified under D1.1. Mention short arc on structural applications and the engineers run!!
To quaify, a full PQR plate must be prepared and tested using short arc-visuals, tensiles, charpy's, etc.
If you must stay in short arc (i have no idea why you would on a vert down), Malcoms technique will work. The big thing of vert down is to use the arc to keep the metal in place and control. If the molten weld metal gets under the arc, you are done. Molten metal is a great insulator and can greatly reduce penetration.
Gas choice is not a big deal. Short arc will happen in any gas atmosphere, even "spray" gases. Gas composition may change volt or amp (wire feed speed) settings somewhat.
Hope this helps a little..
Good Luck
brande
All these notes sure make it easier to understand why more and more companies have converted to Flux Core and Dual Shield.
I seem to remember that Hobart welders used to tell a story about one of their instructors running a beautiful short arc / short circuit weld on plate and basically,pulling the weld off to demonstrate the lack of fusion characteristics.
Just some food for thought
Good luck
