Attempting unsuccessfully to qualify a FCAW-G (75ar/25co2) CJP on mild steel, one inch thk. Attached shows a typical (for us) lack of penetration at the root corners between the backing. Groove is 60 deg total (30 deg bevel). We cannot beat this problem - have tried many different bevel and root face configurations from knife edge to 1/8 face but always end up with the same result and it is only at the root edges as shown. The rest of the groove is clean and perfect. Coupons always pass tensiles and bends beautifully. This particular joint is a wide root gap w/double stringer root passes. Incidentally this is an AWS D1.1 qualification.
Question for the board is this: how much am I allowed to grind down below surface to see if we can erase these flaws? I am thinking that if I allow sanding as much as 1/32" below the adjacent surface I might be able to remove all visible flaws and still be within a reasonable welding tolerance and therefore pass my procedure.
Thanks
edit: The last shot 2310 is a little misleading as the upper scars are the remainder of the backer, not lack of fusion; the two lower lines of scarring are the lack of fusion.
Tom,
Not sure if this a welder or wps qual. If this is a wps qual then I would think that AWS D1.1 (08) 4.8.1.1 (5) might apply. It looks to be inadequate penetration. Failing visual prior to mechanical.
what does the engineer on record say? have you considered switching to another process for the root pass such as GTAW. I'll take a wild swing as I don't normally deal with FCAW and it's typically has good penetration characteristics. My guess is that the backing is acting as a heatsink cooling the puddle by the toes. It might also be a case of welding torch manipulation and really focusing on the sidewalls to get the corners completely.
personally I would reavaluate welding parameters and weld progression and if all else fails, consider using a different process or parameters on your root pass.
then again I am not a fcaw guru so i might be off base
Hello Tom, this is a fairly common issue with FCAW-G and many times most other types of electrodes and processes, especially when a backing strip is involved. I have read articles about the "slag lines" (for lack of a better discription on my part) that considered removal of backing materials to allow for "blending" of these in order to avoid stress risers and crack propagation points. When we consider set-up of these types of weld joints, we stress careful grind preparation of the knife edge of each plate as well as careful removal of any mill scale/rust, or other surface material. Another critical consideration is to have the plates fitted tightly to the backing strip so that no gaps are present, any gaps that exist will increase the amount and likelihood of the conditions that you have shown in your pictures. Gaps will expose the knife edges of the plates to the arc in such a manner that they will be rounded off and allow slag to fill in and form the lines or partial lines of lack-of-fill that you have shown. By paying attention to gun angles you can also minimize the flaws, excessive forehand angles can be a contributor by promoting slag in front of the arc and an increased chance for entrapment. These are just a few of my observations, I apologize for not really addressing your question regarding grinding them out. I await other more qualified and experienced individuals to address your original question. Best regards, Allan
Hogan is correct.
I see roots like this often when operators use a puch gun angle rather than a drag angle
Have also seen this if the root faces are excessively thick....
Voltage setting too high can also make a large bell shaped arc that tends to bridge roots.
Looks like a process control/technique issue
FCAW with gas shielding should have no problems at all fuseing the root in a situation like you describe.
The coupons must be the full thickness to be acceptable.
Is the root wide enough to put 3 passes in the root instead of just two? I agree with using a drag angle vs a push. 30° bevels(60° included) are pretty common, so I would think that should not be giving you any trouble.
Position wasn't mentioned, it would be hard to drag uphill :)
Is this not undercut?
What does D1.1 4.8.1.1 say?
Tensiles and bends are good right?
Js55 I agree with you, measure the depth of the undercut if is less than 1/32" the specimen is visually acceptable.
I have to agree with the responses provided by many of our friendly cast of characters. Technique and possibly welding parameters appear to be the problem.
I, like many here, have seen many welders use a forehand (push) technique with both GMAW and FCAW with the assumption they were obtaining proper fusion in the corners. We usually find out otherwise when we section the test piece and prepare the sample for bending or when NDT is performed.
As for dressing the test sample to remove the incomplete fusion in the root, I don't advise it. D1.1 states there must be complete fusion to the backing (if permanent backing is used). You are simply reinforcing the idea that it is acceptable to have incomplete fusion to the backing for production welds as well as test weldments. If there is slag in the area(s) of incomplete fusion, it is not undercut and the provisions for undercut are not applicable.
I believe you said this was being qualified per D1.1, thus my question is; why wasn't this rejected when you performed NDT as required by D1.1? This should not have passed either RT or UT based on your photographs. As such, the test is done, it has failed.
Is there a reason why you are using a wide root opening? Is the root opening too large to obtain proper fusion with a slight weave in the root pass?
I have many welders qualified for FCAW-G and they have meet the requirement for the backing to be completely fused to the backing as part of the criteria for passing the test.
Best regards - Al
Thanks everybody for the vast array of ideas. As I tried to say in my initial post, we have tried many variations on root gap and face dimensions and always with this same result. I was sure a knife edge would solve our problem - it didn't so we went back to a small root face, I think this last attempt was 1/16 with a 3/8" gap. Our top 3 welders all have all come up with this same symptom. I made sure all kept a slight (~15 degree) drag angle. There is always tight contact between plate and backer (backer is 1/4" thk, so I don't know if the heat sink idea is a contributer). I agree this isn't undercut - it is clearly lacking penetration.
If we turn the heat up, we burn away the edge and lose complete penetration; if we keep the heat down we also lose complete penetration. I thought maybe it was an access problem that's why we went with a wide gap, small face and moderate heat (as memory serves, think we had about 240-250 amps running in this root, root was double stringer).
Al- to your question of why we didn't reject it at NDT - I did three different times. This is our fourth formal attempt although we trialed & errorer it many other times and it IS rejected. We're just scratching for a legitimate loophole.
Regards.
Tom, What size wire are you using? 240-250 amps sounds awfully low unless you're using a small dia. FCAW wire.(less than 1/16") Our 1/16" FCAW wires like to be run around 325amps and 28-29 volts....and our 3/32" wires run around 400amps and 28 volts.
$0.02
Is all mill scale removed from the backing strip and the portion of the test plate that contacts it?
What is your pre-heat requirement?
Tom,
Could you also list the manufacture of the wire?
I'm reading ths at lunch time and may have missed that this has already been addressed. If so ignore it..........
I have had problems with slag, undercut at roots on test plates before. RT (with backing on per D1.5) would show rejectable indications.
Our solution has been to clamp down the plate assembly when tacking on the backing bar - to reduce/eliminate any gap at the root. Then fit strongbacks to the backer side, and hammer in wedges between the backing bar and the strongbacks, to keep the assembly flat and root opening tight. (Once the root passes are made wedges won't matter any more.)
Don't underestimate the effect the root fit-up can have. If you don't have a way to keep it tight while welding, you can actually see the root opening up from heat just ahead of the arc as you travel. So even though it looks good when you started welding, it's opening up as you go along.
Since using this method (for 14 years now) I haven't had an issue with root fusion or slag.
Chet- The wedges are an an interesting trick, might go there later. BUT WHY WOULD THIS BE NECESSARY? THIS WOULDN'T BE HAPPENING WITH TIG OR STICK - IS FCAW-G SO MUCH HOTTER THAT THE PLATES ARE BUCKLING AT THE WELD POOL?
Other particulars that folks have asked about:
flat position (although we will need horiz & vert eventually)
A36 mild steel
no preheat
.045 wire;
wire is AWS A5.20 E71T-12MJ-H8; the manufacture is Kobelco and I have come to love this wire very much. It runs exceptionally clean with not a single incidence of worm holes or porosity in the year we have been using it.
Our fit-ups are shiny metal clean and contact is very good - but I like Chet's idea very much.
Thanks all.
If your asking me I think I'd try to weld it in the 3G (Up) or 2G position, without backing. I'd have the 60* included angle, .045 to 1/16 root gap with a 1/16 root face. I'd have the parts machined, and clean. Have a tight fit. Tack it and sand the tacks. Try it.
Good luck,
Keith
Check your welding parameters against the manufacturer's recommended parameters. Most manufacturer's list their recommendations for voltage, wire feed, amperage, and electrode extension on their web sites. If your particular manufacturer doesn't provide the direction needed, you may want to consider using an electrode from ESAB, Lincoln, or someone that does provide the information needed to properly set the welding machine.
I've had good results when I adhere to the manufacturer's recommendations and I haven't seen the types of problems you have noted. As I said, I've qualified procedures for ASME Section IX and welders per D1.1 without experiencing severe problems with incomplete fusion in the root.
The cost of the electrode is just one cost that has to be considered. Another consideration is how much weld deposited is acceptable without the need for repair. A low cost electrode is no bargain if you can't meet the code requirements. But, I'm sure you don't need me to tell you something you've already figured out for yourself.
Best regards - Al
"BUT WHY WOULD THIS BE NECESSARY? THIS WOULDN'T BE HAPPENING WITH TIG OR STICK - IS FCAW-G SO MUCH HOTTER THAT THE PLATES ARE BUCKLING AT THE WELD POOL?"
I can't answer that, I've never personally run a Tig of Stick PQR - only SAW GMAW, and FCAW. All I can say for sure is that in our case, using strongbacks and wedges has eliminated RT rejections due to indications at the root.
Well... I have to add one qualification to that - it doesn't help if the welder doesn't weld it properly (goofed) or if there is a malfunction of some kind.
But that usually happens when the plate is almost finished and you have the most time, money, and effort into it (Murphy's Law). Like the 3G PQR we did this year - every pass was beautiful - just needed two more passes to cap it off - and something happened so that we lost gas coverage and got big time porosity. I don't try to save those - I just have another test plate welded. But it's disappointing to being so close to a good run ("Welding Olympics").
Tom,
I agree with John Wright; the current (wire speed) sounds low, even for .045. We have very successful results with the same/similar (Manufacturer's Recomended) settings John noted.
Based on your pictures your welders my also have a travel speed that is too fast, or manipulation that is too quick, or both.
-Bert
Topic American Welding Society Services / Certifications / May We Erase Flaws By Grinding the Surface (just a little)?
