Minimum Effective length

Date 06-03-2008 21:59

Hello I'm a welding engineering intern

AS per D1.1 2.4.2.3
(3)"minimum length: the minimum effective length of a fillet weld shall be at least four times the nominal size..."

I'm having trouble finding the minimum effective length of any other joint configuration. Specifically I'm designing and detailing joints that are type GTAW 304 18 Ga. SS. I've had trouble finding any data on minimum effective length either in D1.1 or 1.6. would the 9.1 the sheet metal code shed any light on this situation? I've run into prints I'm revising that have 1/8-1/2 stitch welds or 1/4-2. Right below it it's states that the minimum length of an intermittent weld shall be 1.5" which I assume confirms that it's a bad design, however what about short joint lengths (under 6 inches) or other joint types (groove, corner) etc. Any information would be useful.

I assume that to a welder 1/4-2 or any other short detail would be interpreted as tack every x amount of distance. Obviously autogenous tacks don't seem like a good joint design to me and this seems like a poor detail.

By Bob Garner (***)

Date 06-04-2008 18:16

The minimum length restriction on fillet welds is for design purposes. If you make the weld shorter than 4x the size, then you have to design the weld structurally as if it's only 1/4 as long as it actually is. E.g. if you specify a 1/4" weld that's, say, 1/2" long, than you design it for strength as if it's only 1/4 x 1/2" = 1/8" long.

As far as I know, this requirement is unique to fillet welds and there are no restrictions on lengths of other types of welds. Anyone else know better?

Bob Garner

By Bob Garner (***)

Date 06-04-2008 18:42

I looked in my old engineering texts and the reason for the restrictions to fillet welds is due to the fact that they are somewhat "external" to the actual pieces being connected and therefore the geometry of the joint significantly affects the strength.

Bob

By Metarinka (****)

Date 06-04-2008 19:10

yah I'm curious if there's any other code that calls out for somethign different. Since most of our welds are autogenous on sheet metal an 18ga .(050") weld with legs that will probably roughly equal .050" the effective length would be .2" However .2" is the width of a tack weld. I can't quote it off the top of my head but I believe the AWS D code says tack welds should be at least 1" in length. Practical sense tells me a .2" weld on 18ga is probably too short for structural work... or for anything other than tacking.

I have a feeling things get scaled down different for thin guage work. This is really both a design question and a code/procedure question. 1/4-2 seems like poor detail for a weld to me, and I'm hoping theres something in the book I can throw at the engineers detailing joints

p.s: sometimes I wish I could throw the book (literally) at mechanical engineers

By Bob Garner (***)

Date 06-04-2008 21:16

I took a look at D1.1, Section 1.2 Limitations. It states that D1.1 does not apply for steels less than 1/8" thick; for thin steel, see D1.3 for sheet steel. I don't have a copy of D1.3.

Bob Garner

By Metarinka (****)

Date 06-05-2008 16:59

This goes out to anyone what do you think would be more relevant D9.1 or D1.9 I'm primarily looking for design information, minimum effective length, proper joint detail, allowable gap etc. For structural and non structural 304 sheet and some low carbon steel sheet. I would say the vast majority of our work is non structural, but the service temp can be up to 1300F