Vertical column - verticality

[ehlim1]

When a tall column is installed, what sort of tolerance on verticality is allowed? The only information I can find is in Pressure Vessel HB - 10th edition by Megyesy pg.201, where it defines for vessel over 30' overall length, tolerance = 1/8" per 10' (max. 1-1/2").

I am not sure if this tolerance is for fabrication tolerance (ie. baseplate out of squareness) or installation tolerance. What I need is verticality after installation.

Appreciate if any body can help.

 

[pennpiper]

Of more importance, if this is a column with trays then you need the trays to be level.

 

[mbt22]

It depends greatly on the service. The constraint is likely to be the internals. Kister's Distillation Operation suggests 0.2 deg to 0.5 deg max for structured packings and simply keep the top with 1" to 2" of vertical for a trayed column. There's also the obvious point of ensuring that the verticality spec and column straightness make sense in combination.

Matt

 

[vesselguy]

This is a good topic for discussion.

The value shown in Megyesy is just standard good practice value for a regular vessel; not tray columns.
bmt22 and pennpiper is right that the tolerance should be in line with that specified by the tray vendor. But how is that actually done out in the field is what I like to learn more about. I know you can do laser measurements to plumb the tower. But what if the tray support rings are a bit off? What about the bannana effect caused by hot sun heating one side of the vessel? I have read of sending in a guy into the trays and use a water manometer (i'm sure I'm using the wrong term here but you get the idea) to measure water level on each side (180° apart) of the tray to measure levelness.

 

[zerosum]

Is a "water manometer" what has often been called a Chinese level (garden hose filled full of water concept)?

Verticality can be measured with a transit instrument device, a laser level, or a plumbob offset from the top and measured at the bottom. We have one that a hurricane appears to have caused to lean a bit, and should we elect to go to structured packing, we're going to have to deal it.

I assume that the 0.2 - 0.5 degree limit refers to somehow locally measured levels throughout the structured packing.

0.2 degrees of uniform vertical deviation on a hundred foot tower is around 4 inches, quite a bit. I think it would be discernable by eye.

But determining a local level deviation of 0.2 degrees would seem to me to be not too easy.

This is a good thread. In the near future I may need the input of more knowledgeable people than I.

 

[JoeTank]

Don't get yourself confused by forgeting that the sun may also cause out of plumbness issues. Ideally your would measure when sun is not out... perhaps on a cloudy day.

Joe Tank

 

[zerosum]

Hya Joe Tank,

Do you think this happens even to a column with a couple of inches of calcium silicate insulation? And our process is typically running at 150-250 deg F. But of couse we would probably be making these kind of measurements with the unit shutdown.

I had never considered solar insolation as a factor in verticality, that's a good thing to remember,,,zerosum

 

[JoeTank]

I should have been clearer. It's normally only a concern when the vessel is uninsulated and not yet painted, such as during erection. The brown steel gets pretty hot sometimes and that will cause it to look like a slightly curved banana.

Joe Tank