Trunnion Design for Existing Vessel

[ColinPearson]

In order to design a trunnion or lug to pick up a vessel with, one obvious parameter is the shell thickness. I was hoping to solicit a bit of advice with regard to trunnions welded to existing vessels and how to deal with the possible corrosion.

My thoughts on designating a wall thickness for calculation purposes are to call out a UT tech, take a couple shots in the areas where the trunnions are to be welded, make sure they are pretty consistent with each other and finally make sure they do not fall below where the corrosion allowance spec says the vessel should be for how far into its service life it is.

Unless the corrosion was really minimal, I would then probably take the low end of the corrosion allowance as the shell thickness and proceed with the design.


I guess my question is - How reasonable does this approach sound? The practical effect that I anticipate is a repad that is possibly larger than necessary, but I don't see a huge monetary or time impact (and no safety or mechanical integrity impact) if I tell the craft guys to weld on a 1/2"x20"OD repad as opposed to a 3/16"x16"OD repad. Anyone have any light to shed or opinion to voice?

Many thanks for the input.

 

[jamesl]

If you are lifting a heavy vessel, the trunnion pipe should be welded to vessel wall directly, and cut a repad with holes and fit around the trunnion. You don't want to open up the repad and tear it off the vessel.