Florence12345:
If you are going to be designing lifting lugs and lifting trunnions on pressure vessels, you should certainly know what code you are designing to, and should be pretty darn familiar with that code. Why are you so intent to skinny down the design FoS (factor of safety)? Is it just one part of the whole detail which is giving you problems, or what? Remember, those FoS are there to cover our butts when our design missed a slight overstress, some less than top quality fabrication and welding was done, or the lifting/rigging process doesn’t go quite perfectly, etc. And, on some of these things we really don’t have final control. The general philosophy on FoS and the rigging process has always been the more use and abuse a component can experience (shackles, slings, hooks, and the like) the higher their FoS should be to tolerate this usage and abuse. A lifting lug or trunnion will probably only be used a few times during the life of the vessel, so the reuse and abuse factor can at least be cut back. This doesn’t mean you can skimp on the design, because the one certain thing your client and boss do insist on, is that you don’t drop it. I’ve always felt that top quality detailing, fabricating and welding were more important than the exact material strength or FoS. If something is going to fail (start to fail) it will likely start as some stress raiser, weld imperfection, etc., at a stress/load less than the max. allowable stress. Something that your detailing has caused, not at a high gross average stress. Pay attention to the highly stressed and critical details and welds on the lug or trunnion design them to spec. and detail them cleanly and the rest just falls into place.
