Welding D-Rings

[dozer]

Does anyone have any first hand experience with welding the straps that hold a D-ring to an object as shown here?

To get their full capacity I would think you need full-pen welds. That would require a root gap and a backing bar. My impression is people just throw these things down on a flat surface and start welding.

I asked one of the manufacturers (not the one whose name is on the photo here) but he didn't know his ass from a hole in the ground. Is my idea reasonable or should you make what would amount to a partial-pen bevel weld then reinforce with a fillet weld? Or something else?

 

[Tmoose]

I'd start with the simplified design of a transverse fillet weld as shown here compared to the rating ( one definition of full capacity) -

http://www.nptel.ac.in/courses/112105125/pdf/mod10les4.pdf

I'd expect to be pleasantly surprised i.e. the weld strength would FAR exceed the D-ring rated capacity.

Does the D-ring supplier talk about load rating at different angles?

https://upload.wikimedia.org/wikipedia/commons/0/0a/D-Ring&Weld-on_PivotLink.jpg

 

[kingnero]

Isn't there any instruction that comes with these things?
As said above, getting to a weld size that equals the strength of the shckle shouldn't be too hard to do.
Execution is important though: especially start porosity, end craters and other similar imperfections are to be avoided. Dye or magnetic test would be recommended.

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http://be.linkedin.com/in/fusionpoint

 

[Ron]

Attached is one manufacturer's detail showing fillet welds......

 

[SwinnyGG]

People 'just throw these things down on a flat surface and start welding' because if you do the math, you'll find that the strength of the welds holding the strap down typically exceed the strength of the d-ring by a factor of 10 or more.

Failure mode for these parts, assuming reasonable weld quality, is failure of the legs of the "D" in tension, well before the welds are in any danger.

 

[dozer]

As the drawing that Ron attached shows, they show a fillet weld. I guess they are thinking that is a fillet weld with an acute angle. I would argue that what they are showing is a full-pen bevel weld. I say full-pen because they actually draw the weld nugget and they show it going through the entire thickness of the strap.

This got me hung up on how you achieve a full-pen weld with this but I see the point about the weld strength. In the example that Ron sent, the available strength of the 0.38" fillet welds they specify is 0.6(70 ksi)(0.707)(0.38")(2.88")(2)/2 = 32.5 kips. This is much higher than the maximum load without yield of 4.8 kips.

Thanks for the insight. Next time I'll run numbers instead of assuming. We see what assuming did to me. I do think that this would more appropriately be called a partial-joint-penetration groove weld and the manufacture should call out the minimum effective throat.

 

[SwinnyGG]

No big deal.

While in this case your logic lead to the conclusion that the standard practice isn't inherently dangerous (assuming reasonable weld quality, etc) in my opinion the instinct to question a common practice that your gut tells you might be unsafe is a good one to have.

 

[racookpe1978]

This got me hung up on how you achieve a full-pen weld with this but I see the point about the weld strength. In the example that Ron sent, the available strength of the 0.38" fillet welds they specify is 0.6(70 ksi)(0.707)(0.38")(2.88")(2)/2 = 32.5 kips. This is much higher than the maximum load without yield of 4.8 kips.

The two ends of the simply bent plate are squared off, but they actually intersect the (nominally flat) surface at a 45-60 degree angle. As thin as they are, that 45 degree opening is sufficient for a competent welder to get the near-full-penetration weld root to the plate and base metal.

 

[dozer]

Racookpe1978, I was actually looking at model AJ12A00-DS110 from the same manufacturer that Ron posted. When I laid it out, I got that it intersects the surface at 37 degrees. This is below the minimum angle required for a prequalified weld. As I stated above, now that I've ran the numbers I see that you really don't need much weld. I'm just frustrated that someone would call that a fillet weld. In what world is that a fillet weld?

I showed the D-ring I mentioned on a design drawing a few years ago and I called out a CJP weld. The guys in the shop never called up and bitched and moaned about it so they either just did the best they could and called it a day or actually created a WPS etc. for this. I know which one I'm betting on.

 

[bentwings2]

I work in a custom trailer shop. We also do repairs and modifications.

Typically on a D ring like this I’ll grind the sharp edges back about 1/2 to 3/4 of the way to the inside edge. Then weld both edges. This is a pretty heavy duty part so I try to get a convex weld with no undercut. It takes a lot of weld. I don’t recall ever seeing one of these ripped off that wasn’t rusted most of the way. I’ve seen them badly deformed and buckled even broken D rings but the bracket weld held up.

Even smaller ones that don’t get any grinding hold up. Usually these things are sized far beyond than load they will ever see. Often on repairs we see these welded to much thinner decks and the deck is buckled or torn loose.

Even the aluminum version with a steel ring can be easily welded to suitable aluminum sheet flooring. We seldom do this however. Most are bolt on. Something this size would probably use 4 3/8 grade 8 bolts

Unless you are using these on a cargo aircraft or ship where there might be specific load requirements, I wouldn’t worry too much over the welds if done correctly.

 

[racookpe1978]

In the real world of melted metal ... You're right, technically, the 37 degrees is a tight fit.
But it is an opening, and even with a simple MIG gun, a welder can melt-in the base metal, filler, and plate metal to get a joint.

So, is it a "fillet weld"? = No.
But if the fillet weld calculation is used, you are a bit conservative in the strength because you are using an (assumed) 90 degree intersection angle of plate to base metal. The only "connection" in that true fillet weld is the height of the fillet. And, if it were a single-sided fillet weld, there would be a tiwting force (torque) on the weld since the plate would be pulling(tearing) the joint apart.
With even a "poor" weld prep angle of 37-40 degrees, the weld itself to the base metal and to the plate is much larger than what would be present with a "pure" 90 degree fillet.

And, the error in assuming a fillet weld is on the conservative side, and forces the welder to produce a more substantial leg away from the plate metal edge.