Fillet weld thickness

By pipewelder_1999 (****)

Date 09-30-2008 11:56

I am no math whiz so my explanation may be crude. (9th grade last math class).

On a right triangle the hypotenuse forms a 45 degree angle. If you split the center of the face (hypotenuse) and go from there to the root you have another right triangle. If you then take the leg size and multily it times the COSINE of the Angle which for a 45 degree angle is .707 and multiply that times the leg, you get the throat thickness.

This only works for joints that are at 90 degrees and have flat or convex faces. Here are some facts (unless I am wrong which is possible)

1) an equal leg fillet weld in a 90 degree joint the width of the face is 2 times that of the throat. So if you can only measure the face AND the leg sizes are equal you can approximate the throat.

2) If you can only measure the smallest leg, the throat will be .707 times that dimension.

3) You can only use a throat gage on a flat or concave weld. If a throat dimension is called for and the weld is convex, you must calculate the throat.

By kipman

Date 09-30-2008 12:36

Gerald is on the money. The .707 is useful when you have to measure a concave fillet weld. The welding symbol on the drawing will tell you the required minimum leg dimension (using AWS conventions - it's different in Europe). Of course measuring the leg on a concave weld isn't going to tell you the actual weld size, so you need to measure the throat - problem is the drawing doesn't tell you the required throat size (when using AWS welding symbols). In my opinion this makes more sense than the European scheme because in practice the vast majority of fillet welds are flat to convex and on a convex fillet weld the leg needs to be measured.
So take the .707 (actually 0.7 is close enough) and multiply it times the required leg dimension to arrive at the required minimum throat dimension. Then measure the throat.

Or get yourself a Cam-Bridge gauge from G.A.L. Gauge. It has a handy "theoretical throat" scale - just set it to the leg dimension specified on the drawing's welding symbol and it then works as a go/no go gauge to tell you if the throat is large enough. This won't work with an original Cambridge gauge from the Welding Institute in England, as it does not have the theoretical throat scale.
Mankenberg

By vittorio (*)

Date 10-03-2008 09:57

this is an interesting pape on design of filled weld.

http://www.jflf.org/pdfs/papers/design_file3.pdf

hope this can help

Vittorio

By Metarinka (****)

Date 10-03-2008 17:34

pipe welder explained it well, for convenience I'm attaching a weld strength calculator I made in excel. Among other things if you input leg size it will spit out the effective throat.

theoretical throat is always based off of a triangle, there is no bonus for convex buildup and if the surface is concave than there is a deduction (However Concavity is generally not tolerated that much by most codes)

This only applies to fillets on or very close to 90 degs with equal sized legs. After that you need to break out the calculator and start doing some math.

Attachment: weldstrengthcalculator.xls (608k)

By Bob Garner (***)