Full Penetration Lift Lug Weld

[engpes]

I have a 2.5" thick lift lug that I am welding to an HSS12x6x1/2 joing of tubing. I am trying to follow the DNV requirements of making all lift lugs full penetration, but I am concerned about the tubing wall thickness being too thin (1/2").

This would be a double bevel weld as shown in the attached sketch with each side of the bevel being approximately 1.25".

My questions is this:

1.) Is there any issue with welding a 1.25" (CJP) beveled weld on each side of the lift lug to a 1/2" wall thickness of the tubing member?

AISC section J requires a min and max fillet weld size for connecting member thicknesses, but does not say much on full penetration (CJP) welding size requirements.

I have investigated the local tubing wall for failures and am not concerned about these for the moment. Also, in this particular case I cannot reduce the lug size and I cannot add a vertical tubing column to "notch" the lug into.

Thank you in advance for your help!

 

[dhengr]

Blindly “trying to follow the DNV requirements of making all lift lugs full penetration,” or following that detail seems kinda dumb to me, for exactly your concern/reasoning “about the tubing wall thickness being too thin (½").” You have to know more about the actual loading conditions and the reasons that lifting lug is as thick as it is, to make any common sense out of what’s going on there. The lug thickness is probably set to fit some common shackle size, not because the loads or stresses require that thickness. The stresses in the HSS probably actually control the design in the region of the lug. And, over welding just to meet the CJP requirement might do more harm than good. Look at making the lug .75 or 1" thick and thickening the two doubler doughnuts, then use a CJP. Although, I would not detail that lug with a CJP weld, but maybe a small bevel and reinf’g. fillet all around. Watch the corners so you don’t leave an undercut on them when you make the fillet. You have to round the lug corners before you do the welding. One 2.5" edge or corner (not the sides) of your lug will likely be the critical location for high tension loading, and that’s the area I would concentrate my detailing attention on. Maybe that lug should be shaped differently, so that it puts the loads into the HSS in a different manner. I’ll bet there are four of these lugs to a four legged lifting sling?

 

[engpes]

All that being said, is there any "rule of thumb" or guideline for bevel size base on wall thickness?

I have attached a plan view of all 4 lugs.

I will try to avoid any future "dumb" designs. Thank you for your assistance.

 

[fegenbush]

The rule of thumb is fillet leg equal to the thickness of the thinner material being joined. If using E70XX or equivalent, this would (using axial loading) cause the base metal to govern the allowable load.

 

[dik]

CIDET research has indicated that for HSS, a weld that is approx 10% greater than the tube thickness provides nearly a CJP weld... that's for connecting HSS... not heavy plate... you would likely have to use yield line to determine the capacity.

Can a regular fillet weld be used to secure the lug... 1/2" or so, likely a 3 pass or whatever...

Dik

 

[engpes]

Fegenbush

I am aware of the fillet rule for base metal thicknesses, but I was wondering if this should be applied to bevel type welds.

I have already investigated all of the local moments, shear punching, etc and my concern is whether the heat from the large bevel weld will be problematic (crippling) for the base metal.

Thank you very much for your help!

 

[dik]

sorry... that's CIDECT...

Dik

 

[MollyK]

Minimum fillet weld requirements in the AICS manual only apply to fillet welds. There is no rule or standard (as of yet) in the AISC code for penetration welds. As long as all other checks were completed, this connection is adequate. I also agree with dik, the yield line analysis for the hss member should be checked due to the relatively thin walls.

 

[engpes]

Thank you very much MollyK!

 

[connectegr]

In your case the oversized weld size is a practical issue. The CJP weld on a 1/2" HSS wall will be limited in strength. There is not a limit on the size of weld by AWS. Some consideration for the amount of heat and deformation of the HSS wall may be required. Weld shrinkage will result in significant residual stresses. I think some of the comments above are intended to suggest that a reduced weld size, PJP or fillet weld, will provide adequate strength with less issues in application.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.

 

[dik]

connect...

Couldn't have said it better... good explanation...

Dik

 

[dhengr]

Engpes:
The outer 2.5" edge and more specifically the outer corner, where the lower circled 7's (part #’s) point, are the critical locations on those four lugs. You don’t mention the loads on the lugs and the vert. dimensions and angles of the slings, or the dimensions of the lugs. So, it’s difficult to get a feel for the forces or weld stresses on the lugs, but there will be tension, shear and a bending component on those outer edges and corners. And, one difficulty is that at that critical corner you have to fill (weld) for the radius of the HSS; plus, on those short bevel welds you have a dozen starts (or stops), each of which is a potential stress raiser or defect spot. Then on the inside edge of the lug, your reaction is in plate bending of the .5" HSS horiz. wall, which will produce prying or secondary bending out near the critical corner. Tri-axial stress and residual stress hardly begins to describes it. Do you still have the option of modifying the design and shape of those lugs? It would be better to use a thinner lug and get those forces directly down into the vert. walls of the HSS, rather than through the horiz. wall plate bending and around the HSS corner radii. Could the lugs be shaped and sloped to match the sling leg lines a little better, in which case they would impart more of a tension and shear force on the top wall of the HSS? I don’t know if you are the designer or fabricator of this skid, and I don’t know of any rule of thumb that says you couldn’t make the CJP welds; it’s just a lot of extra welding if the loads don’t call for it, with each pass and start and stop introducing potential problems and defects. I don’t have the DNV codes, do they req’r. the CJP welds, with no work-around? I find it hard to believe that that lug needs a 2.5" CJP weld. That just seems like an ill proportioned lug and weld detail, the bevel is almost as deep as it is long. I’m not pickin on ya, I’m trying to get you to think of a cleaner lug detail, all the way around. The stresses you checked may not be too high, but if the design and fab. introduce secondary effects, stress raisers or defects they will control.