Full-Pen or multi-pass weld 1

[bvass]

Hi All,

I have a simple question that I'd like to get some opinions on. My firm is designing some heavy moment connections for industrial pipe racks that use end plates bolted to column flanges. The connection from the end plate to beam is typically a 5/16" max fillet weld. We have some locations where larger than 5/16" welds are required and start getting into multi-pass sizes. My supervisor is of the opinion that full-pen welds are more cost effective than a multi-pass (say 3/8" max 3-pass) welds. I just wanted to get some general opinions on this matter because to me that does not seem like a cost effective solution. Full-pen requires grinding and special inspection, a multi-pass welds required more weld metal but no inspection or grinding. Intuitively I would think a multi-pass filet would be the way to go but I could be wrong. Opinions?

Thanks,
Brad

 

[gtaw]

Complete joint penetration groove welds only require volumetric examination when specified by the Engineer if AWS D1.1 is the welding code imposed. The only welded connections that have mandatory volumetric examination requirements are connections subject to fatigue and are loaded in tension. You can read the particulars if you check clause 2.19 in D1.1:2010.

Best regards - Al

 

[MintJulep]

I suspect that there is confusion on terminology, and that when your supervisor says "Full-pen" weld what he really has in mind is a bevel weld, or bevel-T weld.

Step 1, make sure you are speaking the same language.

Yes, there may be grinding involved. But grinding is generally done by a helper, at helper rates, while welding is done by welders, at welder rates.

 

[wannabeSE]

There have been numerous articles in Modern Steel about economic welds. Here are links to couple

http://www.modernsteel.com/Uploads/Issues/January_2013/012013_steelwise.pdf

http://www.modernsteel.com/Uploads/Issues/May_2008/052008_30777_steelwise_web.pdf

 

[racookpe1978]

Worse case condition - and a 3/8 fillet weld is very difficult to get 100% good welds in 1 pass ...

If you have a root pass and 2 cover passes for a large weld, the chances of screwing up all three welds at the same point is just about 0.

If you have one very difficult weld made with just one pass to fill that much weld metal correctly, the chances of a complete weld with no failures at all is about 0. What is your penalty for failure?

 

[gtaw]

Depending on your design criteria, the allowable unit stress for a complete joint penetration groove weld is the same as the allowable for the base metal. The allowable stress for a fillet weld is .3 times the tensile strength of the filler metal, but it can't exceed some value specified by the design standard for the base metal. In the case of structural steel per AWS D1.1, the limits are 0.4 times the allowable shear and 0.6 times the allowable tensile strength. That keeps the designer from using a high strength filler metal on a lower strength base metal and forcing the failure in the base metal. Ideally, the strengths should match.

In some cases it is simply easier to make the fillet weld bigger than it is to prepare the base metal for a CJP and either use a backing or double sided groove with a back gouge operation to ensure the weld is sound.

Best regards - Al

 

[bvass]

Thanks for all the responses. By full-pen I do in fact mean full-penetration or CJP, I thought those terms were interchangeable. The articles had good info in them too, and I do believe in this particular case the multi-pass fillet is the best option. Thanks again!

Brad