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Groove weld backed up with a fillet weld

Groove weld backed up with a fillet weld

Hello, Just a general question here:

On many occasions now I have worked with 1970's vintage prints for large industrial machines (mostly presses). These presses are often heavy plate weldments in the 2-6" thickness range. I have noticed on a lot of these prints that it is common for a large plate to have partial penetration groove welds that are backed up with a fillet weld of equal or smaller size. By this I mean for example a 1" x 45 deg. groove weld that is filled to flush with the edge of the plate, then a 3/4" or 1" fillet weld added on top afterwards. They appear to be used in all sorts of orientations/directions of loading.

My questions: Is the fillet weld adding any strength to the groove weld? I was under the impression that the throat area of the groove weld would be equal to its groove depth, and that for a 45 degree fillet weld it would be .707 of leg length, which would be smaller (and therefore weaker- not really adding anything?) Also, how common of a practice is this type of weld nowadays?

Thank you.

RE: Groove weld backed up with a fillet weld

Are you referring to two structural members joined at an angle (up to 90 degrees), attached by a partial penetration groove weld followed with a fillet? Or are you referring to a butt weld between two members with a fillet added?

RE: Groove weld backed up with a fillet weld

Two member joined at 90 degrees

RE: Groove weld backed up with a fillet weld

Ok. The fillet weld in this specific case is to reduce stress concentration at the T-joint. The fillet is added for improved transition or geometry versus a square corner.

RE: Groove weld backed up with a fillet weld

I see, that does make sense. Thank you.

RE: Groove weld backed up with a fillet weld

The fillet not only improves the geometry at the sharp reentrant corner, but it also significantly increases the weld throat, so the regular weld stress is much lower.

RE: Groove weld backed up with a fillet weld


Can you elaborate on this? I had originally thought that the smallest throat dimension of the combined welds would be equal to the groove weld depth, and that the fillet weld wouldn't really increase this.


RE: Groove weld backed up with a fillet weld

I think I see it. If I consider the throat to be from the root of the original groove weld to the face of the reinforcing fillet weld, that would certainly be larger than just the groove depth. Is that what you are saying?

RE: Groove weld backed up with a fillet weld

The small fillet throat length is additive to the groove weld length. The fillet will help to increase the load capacity or reduce the stress on the weld.

RE: Groove weld backed up with a fillet weld

Hi Mod 231,

I think I see a hydraulic cylinder off to the right in the drawing.

Could you provide a larger hunk of drawing to help me see what the load path might be in the frame ?


Dan T

RE: Groove weld backed up with a fillet weld

Unfortunately I can't without doing a ton of work to blot out proprietary notes, which wouldn't leave much left to look at in this case...

The weld I had pointed out happened to be on a main plate loaded primarily in shear.

In any case, I feel like I have gotten the info I was looking for. Thanks to all who responded.


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