Weld size

Date 03-18-2009 11:05

I have always been under the thinking that a fillet weld between two different thickness metals would require a weld size equal to the thinnest member unless otherwise specified by engineering. We are currently reviewing some of our drawings and have found a sitiuation where we are welding a piece of 1/2" diameter pipe with a wall thickness of .109" to a coupling that is probably about .250". The required weld to the drawing is .250" fillet weld. I am thinking that this is overkill seeing that the one base metal is only .109". Can anyone give me any idea of why this weld would have to be this big? Wouldn't the maximum strength of this joint be based off of the thinner wall regardless of use? Maybe I'm I'm not understanding something. A design engineer I am not. Thanks for any info.

By Bob Garner (***)

Date 03-18-2009 14:36

As a design engineer, I don't think this weld is correct, either. I agree with you.

Bob Garner

By Kix

Date 03-18-2009 15:43 Edited 03-18-2009 15:46

Oh yeah, don't ya know, bigger is always better. ;-) lol kidding... You are correct in what you are thinking. It happens all the time, it's always a good catch and a relatively easy one to fix. Another good one is when welding on lets say two pieces of 1/4" thick material in a fillet weld on both sides, they don't need to call out a 1/4" fillet size just because they're welding on 1/4" material.

By jsdwelder (***)

Date 03-18-2009 16:21

Ya know I think that the "bigger is better" thinking happens all too often. As far as a relatively easy fix, with this customer nothing is an easy fix. I was told that unless you can justify a cost reduction to us, then it is what it is. Well in the case of this weld with a total diameter of .5" x 3.14 whatever that is say, 1.5 " circumference,they won't see a big $$$ difference. It's just the point of why would you call for such a large weld on .109 wall??????????

By Superflux (****)

Date 03-19-2009 19:23 Edited 03-19-2009 19:52

Weld sizes on piping and vessels are designed not only for the mechanical reasons obvious to us welders. On large vessels and tanks, there are reinforcing pads. This is not only to reduce warp, but to replace the material that was removed. So, on smaller assemblies, oftentimes an oversized weld is called out on the print to replace the "hole" (missing mass). This is more cost effective than the laborious hassle (and unaesthetic) of fitting and making the extra welds required to install a mini re-pad.