V Groove v. Bevel Groove

By Blaster (***)

Date 02-09-2015 20:47

One of my students was repairing an excavator bucket thumb over the week end. The thumb was made of 1" plate of unknown material type. He was welding a new set of ears to it. So in short, he was doing butt joints on 1" plate. He prepped a bevel groove about 3/4" deep with the plan to back gouge and back weld the joint for full pen. We do joints like this in the school regularly and the student is very proficient with this kind of work. He was welding with E71T-1.

His supervisor told him that due to the unequal surface area where fusion would be taking place, that this very highly stressed joint would somehow be more likely to break than if he set it up as a V-groove.

Now I have never heard of such a thing, and applied countless bevel groove joints on structural connections. But being an open minded guy, I figured I would ask here to see if the experts where aware of something I wasn't... so, is there a valid reason why a V groove would be superior to a Bevel groove in longevity, assuming both were applied soundly and using good workmanship?

By Lawrence (*****)

Date 02-09-2015 21:22

My stance would be that *when* both are prequalified joints, that the code is intimating that decades of experience have revealed that quality and consistency are readily produced and maintained.

Those different joints contain different volumes and this can have an effect on distortion and productivity in making the welds... But for a one-off repair I really see no reason to disallow a single bevel as long as the operator can get the root pass clearance needed.

a properly placed CJP weld is no more likely to break than the base metal, whether it's a V-groove or a single bevel eh?

By Blaster (***)

Date 02-10-2015 01:48

That is the assumption I always made... but I am gun shy of thinking of anything in absolutes... except maybe things of a political nature!

By welderbrent (*****)

Date 02-09-2015 23:08

I'll add one more twist to your considerations: often, not always as it depends upon manufacturer and excavator size, the leading edge plate on those buckets are not A36. They will have higher carbon content of varying amounts. The material in the forged tooth bracket is also occasionally not kind to using only 7018.

Having said that, I have repaired more than a few quite successfully with 7018 or equivalent wire electrodes. But make sure you preheat. Then, I have found 8018 to be somewhat more dependable.

Again, 7018 has welded probably a higher percentage of these than any other electrode. Take your pick.

Re-read your post, are you talking about the tooth holders or the attachment brackets to connect to the end of the excavator arm? Could be the same, not A36, and would work better with 8018, but, I have totally rebuilt buckets with all 7018 and they have lasted fine.

Remember, there is a difference between how a building structural weld will experience stresses compared to how an excavator will experience stresses. There are many joints on heavy equipment that will benefit from using V-grooves instead of bevel grooves.

Just my two tin pennies worth.

He Is In Control, Have a Great Day, Brent

By Blaster (***)

Date 02-10-2015 01:45

Brent when I used to manufacture buckets, we used T1 steel for all leading edges and wear bars. 4140 for the bushings. The rest was mild steel. We welded the cast steel tooth adapters with E70T-1 wire... actually we welded the entire bucket with that wire.

Right, those parts are under extreme stress and cyclic loading. The crux of my question goes back to whether there is a reason (and what is that reason?) why one joint would be superior to the other, again given both were applied by an adequately skilled welder that had the skill to put either weld in correctly and soundly.

By welderbrent (*****)

Date 02-10-2015 14:49

T1 was our norm as well but there are others. And, as I noted, while 8018 and 80 series electrodes was 'more' compatible, 70 works very well but must be done with stricter adherence to good welding procedures.

Normally, when one would be considering a bevel groove on these applications the bevel would be on the cast part with the 90° remaining on the edge of the T1 plate on the leading edge of the bucket. The stresses then will come evenly through the grains of the bucket with a straight through shot aided by the slight weakness from the heat affected zone even with good preheat and welding procedures.

When utilizing a V-groove the stresses come through diagonally which gives more surface thickness and distributes the stresses instead of allowing them to tear through at a concentrated point of weakness. Similar to how a concave fillet distributes stresses better than a convex fillet even though in many structural applications it is not a point of consideration. Again, on our heavy equipment we strove for concave fillets with proper throat thickness in order to get an even stress distribution. Stress risers are a much smaller consideration on concave fillets.

Now, we had a cross sectional analysis at a former place of employment many years ago that demonstrated this condition and the advantage for strength and stress distribution from using a V-groove instead of a bevel groove. I may not have explained it real well here and as I am not an engineer it remains to be seen if it would hold up to research scrutiny.

But, I know we incorporated this into our shop and field repair practices and 'appeared' to get longer service out of V-grooves than bevel grooves.

Is it enough to make an issue out of? Good question for consideration. I sure would not encourage a student to challenge an employer/customer without a lot more information. And even then, one must know how to appeal to authority and offer creative alternatives in a humble and meek spirit.

He Is In Control, Have a Great Day, Brent

By Blaster (***)

Date 02-10-2015 01:38

Al do you know if this prohibition is based on metallurgical / heat input issues and/or stress transmission issues, or rather simply because a marginally skilled welder is more likely to have soundness problems with the more demanding bevel groove?

Side note: I continue to advocate for D1.1 to adopt qualification testing with bevel grooves as opposed to V-grooves. BGs require WAY more skill and are used extensively in the field while qualification testing is currently done with much easier V grooves. That has never made a lick of sense to me.

By 803056

Date 02-10-2015 16:19 Edited 02-10-2015 16:21

I think you answered your own question.

I don't sit on the D1 committee, so I have no idea of their reason for the restriction, but I do agree with your observation and your conclusion.

I recently completed a project where I trained 43 welders to weld in all positions using FCAW. Of the 43 trainees, all experienced welders, but not experienced with FCAW, 37 of them passed the qualification test. Of the 37 qualified, 24 were put to work welding and the remainder served as support personnel for the welders.

Each of the welders were required to pass a qualification test on a single bevel groove on 3/4 inch plate. The root opening was about 15/16 inch on 3/8 inch thick backing. It closely replicated the groove configuration the welders would be working with on the project. Several of the welders questioned the groove because it wasn't like any test they had taken before. Once they got on the project, the same welders said, "Now I understand why you tested us the way you did. It makes sense now and now we know exactly how to handle it." The best comment I heard was, "Why aren't all the AWS tests done using the single bevel groove. It is what most of the welding in the field is." I find it difficult to disagree with the truth.

The project involved the installation of about 30 000 pounds of 1 inch plate and roughly 3500 pounds of deposited weld. All the welding involved horizontal, vertical, and overhead CJP groove welds. All the welding was completed in 12 days. I would provide more details if I could, but due to the nature of the work, it can't be shared.

Best regards - Al

By JTMcC

Date 02-11-2015 21:09

If nothing else, it's a real world learning moment for your student.

Through his career he will have many "supervisors" and others, impose conditions that may have no standing in reality. That's just how it is : )

J