Welding - Complete Joint Penetration
Welding - Complete Joint Penetration
(OP)
Hi All,
Is a Complete Joint Penetration possible in a case where a Lifting Padeye/Lifting Lug is much more thicker than the plate it is going to be welded on. The padeye/lug thickness is 35mm, whereas the plate is 10mm thick only. We cannot do any bevel preparation on the plate. Thanks in advance.
Regards,
HD
Is a Complete Joint Penetration possible in a case where a Lifting Padeye/Lifting Lug is much more thicker than the plate it is going to be welded on. The padeye/lug thickness is 35mm, whereas the plate is 10mm thick only. We cannot do any bevel preparation on the plate. Thanks in advance.
Regards,
HD






RE: Welding - Complete Joint Penetration
1) What is proposed weld geometry and your proposed weld prep angle and depth.
2) How do propose making a weld be "stronger" (more area across the weld cross section) than the thinner of the two base metal thickness that it is joining?
RE: Welding - Complete Joint Penetration
It is more than likely that a full penetration weld on the 35mm lifting lug plate is not required. The padeye thickness is dictated by one set of criteria, which pretty well sets that max. load on that padeye. Good detailing then shapes the padeye down to the lifted piece and usually allows plenty of weld length to carry the load, without it being a full pen. weld. You can actually do damage to the equipment when applying welds larger than needed. Good weld design and detailing are very important to make these lifting lugs work properly, without stress raisers and the like. You should really get someone who knows how to design lifting lugs to help you with this.
RE: Welding - Complete Joint Penetration
Thanks. Calculations have been done for partial bevel and fillet welds, which are good for the loads with Safety Factors included. Its just that some codes requires all lifting padeyes to be full penetration.
Dhengr,
You mentioned equipment damage when applying larger welds. What will be the general rule, when applying a normal fillet weld. Say for example there are two plates to be joined one is 10mm and the other is 20 mm and all calculations from different load angles (incl. FOS) specifies that the weld size required is 5mm only. Just to be more conservative, I apply a weld size equal to the thickness of the smaller plate of the two to be joined. Will a weld size equal to the thickness of the smaller plate cause damage?
Thanks.
HD
RE: Welding - Complete Joint Penetration
RE: Welding - Complete Joint Penetration
Most of the design codes have some tabulation of min. and max. weld sizes as a function of the plate thicknesses in the joint. These tend to be fairly prescriptive, with some of the more detailed welding codes offering some commentary on the matter. Good weld design literature discusses the matter, but to some extent it boils down to engineering experience and judgement. Welding is expensive and more, unneeded weld passes and joint preparation add to this cost. The heat input from welding causes distortion, locked in residual stresses, potential for more defects and stress raisers, sometimes changes mechanical properties of the materials being welded if not done properly, etc. etc. So, a good rule of thumb is to design the simplest possible weld, usually a fillet weld, of sufficient strength to carry the loads; and beyond that you may be doing as much harm as good if you are not very careful. More is not always better, certainly not cheaper or without potential consequences. Then, spend your design time designing nice clean details, with simple load paths, and minimize stress raisers and stress concentrations. Much of this comes with engineering experience on designing welded joints, and this type of equipment. For example, in your case, how does the 10mm pl. receive the stress from the welds, can it take it without buckling, being over stressed, etc.? Then what good would a larger weld do? The thickness of the lifting lug is mostly determined by the opening on the req’d. shackle, to protect the pin, and the lug stresses in that immediate area. And, that can be finessed by adding doubler pls. at the pin hole. But, why would this thickness dictate the weld size? I’ll bet in you case that a 15mm lifting lug with two 10mm doubler pls. would have worked just fine. Then shape the lug so you are not putting an unprotected weld termination in excessive tension. Within the Mech. community and in some of their codes, and project specs. there does seem to be a misinformed idea that since the joint btwn. the web and flange in a rolled steel beam, channel, angle is solid (a function of the rolling process, not actual load transfer need) all similar joints must be solid too (full pen.welds). This certainly saves time in actually designing the weld, saves even needing to know how, at considerable welding cost and other potential problems.
Wadavis:
As for reading material... The AWS code is a good place to start, get a copy. Omer W. Blodgett, Lincoln Arc Welding Foundation, has a number of good books, and they are inexpensive too, and very good on the basics, the way an engineer should think through a design problem: “Design of Weldments,” “Design of Welded Structures,” “Metals and How to Weld Them.” ASME BTH-1, “Design of Below-the-Hook Lifting Devices” covers padeyes, etc. and is pretty much the bible in the U.S.; and DNV and others will have similar codes for lifting equipment. You will find that good weld design and detailing is the same in most cases, irrespective of the exact structure.
RE: Welding - Complete Joint Penetration
Thanks for the explanation, and time.
Regards,
HD
RE: Welding - Complete Joint Penetration
As HD said, thanks for your time and the recommended reading.
wadavis
RE: Welding - Complete Joint Penetration
RE: Welding - Complete Joint Penetration
Your comment about some codes requiring the full pen weld makes sense if the lifting eye is assumed to be sized for a given load, and if it does not have a load path equivalent to its own load capacity, it would create a potential safety issue. That said, it seems to indicate that your lifting eye may be oversized for the application. I can see that this would be desirable for several reasons; reduction of stocked items, standardization, using available components due to lead time. If the lifting eye is rated and labeled, it would follow that a reduction in weld size for a smaller load would be acceptable as long as the device rating is clearly marked with the new rating.
RE: Welding - Complete Joint Penetration