API650 - drain-vent holes on roof supporting columns 2

[ghkskn]

API 650 leaves it to the owners decision but is it a general practice to open drain and vent holes on roof supporting columns (12" 16meters) so it will not try to float.

Thanks for the comments..

 

[IFRs]

Vent holes are critical to safe work in the future.

 

[JStephen]

As far as I can tell, the idea of a column floating off it's base is just a non-issue. I have seen requirements that columns be non-buoyant, but have never seen a problem caused by floating columns.

There are two theories on the issue of the vent holes (which are not normally intended to prevent flotation, anyway). One is the keep-it-out theory and one is the make-it-cleanable theory. If you put in the vent holes, you get product in the columns, but can't paint in there, so you may have corrosion problems. If you seal the columns, and they stay sealed, no problem. If you seal them, then product leaks into them slowly, but won't drain out readily, you run into the problem IFR is getting at.

 

[JoeTank]

JStephen,
Tall water tanks (standpipes) sometimes have large diameter columns governed by l/r ratios. As a result they occasionally will try to float. I've only seen it occur a couple of times... on paper, not in service.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com