Maximum Weld Size 2

[dik]

I have a 1-1/4" thick lifting lug that I'm welding to a 3/8" thick stiffened stack using a fillet weld. The weld is not located near a seam in the stack.

What is the maximum size fillet weld I can use for the lifting lug to stack connection? I've typically used 3/8" maximum for this based on the minimum material thickness, but, may need to go a little larger.

The material is 304L stainless and failure will be through the base metal and not the weld. The use of 3/8" has been for distortion and cracking control.

Dik

 

[desertfox]

Hi Dik

I was always told you can't have a fillet weld larger than the smallest material thickness in the joint.

Desertfox

 

[dik]

Thanks, fox...

I've stretched that a bit... in particular for HSS... Cidet has tests that show if weld thickness is 1.1x wall thickness, a weld approaching a full penetration weld is produced. I usually stick to min. thickness for distortion and cracking reasons. I was just wondering if there was an upper limit...

Dik

 

[desertfox]

Hi Dik

Your welcome, I found this while googling however even after the fillet weld is reinforced, the reinforcing is not taken into account for the weld strength.

http://books.google.co.uk/books?id=...v=onepage&q=reinforcing a fillet weld&f=false

 

[dhengr]

Dik:
I think you could pick up a little weld size by grinding or nibbling an 1/8" bevel on the lug. That increases the weld throat to .707(1/8 + 3/8) and increases the weld size to 1/2" at the base metal where you have to use the strength of the base metal for design stresses. It’s still at lease a two pass weld. You might want to increase the bevel on the 1.25" sides/edges of the lug where the stresses are probably the greatest. And, at the four corners, when you are welding all around, you have to be very careful that you don’t leave a notch in the corners on/of the lug, right at the toe of the weld on the lug. That happens because the weld puddle tends to slough down right at those sharp corners, that shape just won’t hold the puddle as it solidifies. You can usually solve this problem by grinding the lug corners to about a .25" radius, to some distance above the weld, this will prevent the sloughing.

Instead of a 1.25" thk. lug, why not a wider lug, but only .75" thk. with two .25" thk. doughnuts at the shackle hole, one each side and welded all around to the .75" thk. lug? This way you can pick up weld length, rather than increasing the weld size.

 

[dik]

Thanks dh...

The padeye is already 16" wide... and the proposed shackle just fits...

Dik

 

[racookpe1978]

OK. So you pick up the load through the shackle through the big-fat-long lug through a fillet weld large enough to carry all of the load.

The lug and shackle are good. They don't break or tear off.

When does that little 3/8 plate AROUND the lug and its fillet weld bend and tear itself off due to twisting and shear stress?

How much is the ultimate weight being picked up by that single (very, very large!) lug? What is the moment arm generated when the second (or third) large lug is NOT assuming its assumed portion of the load - when the crane lift ISN'T at its assumed perfect symmetry but the whole load is only on two of the four lugs?