Calculating Load capacity of Welds on Lifting eyes/ Lugs

[CMMehanicalWorks]

This may be in the wrong section but let me know if it is, I work in the Mechanical construction industry (Oil and Gas) and I have come across times where it would be beneficial to know how much of a weld is required in order to ensure the weld is sufficient to hold a lifting EYE/LUG to an embedded plate in the ceiling while a load is suspended from it. I have been in contact with welding engineers who are unable to tell me, and in the past we have had to use alternative methods to lift Pumps, Skids pipelines valves and headers as nobody is able to submit calculations to determine the load capacity. Any help of links to websites or books would be a help. Thanks

 

[desertfox]

Hi
Try this site:-

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html

 

[kingnero]

If the welding engineer is unable to tell you, they shouldn't be doing what they do.
Even if everything is unknown, you can measure the welds, assume low-quality carbon steel (fy=235 MPa), and deduct a % for bad quality welds. That takes 5 minutes, including searching for a ladder to reach the lifting eye on the ceiling.

Certainty is hard to achieve, because those welds are typically hard to NDT. But you sure can achieve workable results using this method above.

Provide a sketch so we can explain it more clearly in detail.

 

[dhengr]

CMMehanicalWorks:
What seems like a pretty simple and straight forward question, is really pretty complicated if you are going to do it right. And, you better do it right or you could drop a pump on someone’s head. You should develop a relationship with an engineer who can help you with these sorts of problems. And, don’t assume he is just there as an insurer of last resort, or someone you can sue if things go wrong. They don’t like working for people who think that way. He is not clairvoyant, doesn’t have x-ray vision, etc., there is still plenty of leg work for you to do to get him the info. he needs to give you an answer; or you can pay him to dig it out. Actually, designing the lifting lug and its weld is the easy part.

Desertfox’s link gives some good info. on general weld design, and there are other ref. texts on weld design if you are really interested. But, there are also a number of questions that you must answer, dig the info. out and then guarantee for your work to be successful. Are your welders qualified, do you trust their welding, are they qualified to do overhead welding? What is the embedded plate, is it actually weldable, by what processes and welding rods, etc., how is it fixed to the structure above to take your load? These are actually questions you should be taking up with the building owner during the initial bidding process, so you can plan and price your work. When you go to an outside engineer with these questions, you are asking him to trust that that plate didn’t just fall into the bottom of the form before the conc. was poured. All he can see is the width of the bottom flange of a beam, he has no other info. on the strength of that beam, or the conc. or the ceiling system/floor system above. Your engineer has to work with the bldg. owner, and have access to the original bldg. plans to start to solve this problem. On some bigger jobs these lifting points are designed and certified, and left in place, so your question doesn’t come up. They know that heavy equipment is going to have to be installed and serviced so some of these lifting points are designed into the structure and should show up on the plans for the benefit of future users.

 

[tbuelna]

Overhead lifting structures usually require a FoS of 5.0 by analysis. And for weld joints there are usually additional knock-down factors for weld quality, weld defects, the type of NDI used, the material that is welded, and whether any stress relief or heat treatment is used post weld.

 

[Rich2001]

Though dated in MatCad 7 format this site has a pdf and mathcad sheet to assist in the design of lifting lugs.

http://www.pdhcenter.com/courses/s106a/s106a.htm

Richard

 

[kingnero]

What dhengr mentions is true, you need to know the entire picture for a complete analysis, but to answer the specific question CMmehanicalWorls asked, I refer to my previous answer.

If you load a certain weight and the beam to which the eye is connected fails, no-one will point at the welding engineer that said the welds will hold a certain weight.