Lifting lug design with corrsion allowance?
Lifting lug design with corrsion allowance?
(OP)
Hi All,
One concern just popped up in my head, when you design a lifting lug, do you normally included a corrosion allowances(for carbon steel)?
Normally carbon steel lugs will be painted, but no matter how good the paint it is, after couple lifting (eg, installation), the contact area paint will be scratched off, and the structural will sit there and the lug will starts to rust, in few years time, when the structure will need to lifted again, it lifting won't have the same meat on it as it was new.
Any comments?
One concern just popped up in my head, when you design a lifting lug, do you normally included a corrosion allowances(for carbon steel)?
Normally carbon steel lugs will be painted, but no matter how good the paint it is, after couple lifting (eg, installation), the contact area paint will be scratched off, and the structural will sit there and the lug will starts to rust, in few years time, when the structure will need to lifted again, it lifting won't have the same meat on it as it was new.
Any comments?





RE: Lifting lug design with corrsion allowance?
Normally lifting lugs are designed with a pretty big factor of safety (3, 4 or 5), so they should be able to tolerate a little corrosion over time. They should also be, at least, visually inspected prior to reuse after a number of years. Why not save a quart of the paint and hide it someplace on the skid, with instructions that all scratches be cleaned and touch-up painted after the skid is installed. Alternatively, if it is just the lifting lugs, why not have them rub some grease on any exposed steel when they are done with the lifting. There’s half a chance that the grease will already be there.
RE: Lifting lug design with corrsion allowance?
Thank for the reply,
Just reading from ASME BTH 3-3.3.3, pinhole should be drilled, reamed to surface finish of min 12.5micron, ones it starts rush on the pinhole, there is no guarantee of the surface finish finish for next use.
re design safety factor, I tend to use one safety factor for on aspect only, and I don't think using the structural load safety factor to cover corrosion issue is an good engineering practice.
re procedure/instruction, should be given for installation/operation/maintenance, but implementing of them along the line is another story.
RE: Lifting lug design with corrsion allowance?
Aerospace stores lugs were traditionally Cad plated, though we were starting to use zinc on some.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Lifting lug design with corrsion allowance?
Regards,
Mike
RE: Lifting lug design with corrsion allowance?
I would suggest to liquid nitrate the piece, thus removing free iron from the surface. Then no rust at all and you get a good increase in hardness to mitigate metal-to-metal transfer or galling.
Regards,
Cockroach
RE: Lifting lug design with corrsion allowance?
I wouldn't worry about it. If lug shows signs of deterioration, replace it. it will be less expensive than using a SS.
- CJ
RE: Lifting lug design with corrsion allowance?
I mean a sky hook doesn't rust away to thin air over it's lifetime of usage! So I'm not sure where that concern comes from. There is a mental illness about being too safe, unfortunately all around us. I'm not talking about professional, well seasoned or schooled engineers, but the tradesmen themselves. Safety also acknowledges practicality and reasoning, so I think you're just being over cautious.
Regards,
Cockroach
RE: Lifting lug design with corrsion allowance?
Wouldn't have been nice to have the resouces today 20 years ago? You just had to use common sense and engineering judgement. If you did make a mistake, you learned lessson. He should jsut go to his Sr. and tell him what he wwants to do and why.
- CJ
RE: Lifting lug design with corrsion allowance?
We've also seen lifting tabs for tank covers orientated incorrectly putting the tab in a bending attitude along with pure tension.
Also we've seen four lifting points with the total load divided by 4 and no regard for the center of gravity of the load - where sometimes one lug will be taking a much greater load than some of the others.
RE: Lifting lug design with corrsion allowance?
Regards,
Cockroach
RE: Lifting lug design with corrsion allowance?
Regards,

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