Maximum Value Of Bending in Columns 1

[Wrl69]

Hello,

To design of pressure vessels under ASME Sect. VIII, what is de maximum value of tolerance for bending (deflection) in vertical columns. By some document I found 6inch/100ft; That is true?

Thanks.

 

[gramya]

The good engineering practice for petrochemical and chemical plants indicate that the deflection of the tall verticla vessel shall remain within 5 mm per meter which works out 6 inches for 100 ft. All good consultants for project engineering follow this criteria and it appears in their tech spech for design criteria. However the final say will be the detailed stress analysis done under such wind load, piping load conditions causing bending moment and deflections to the tall columns and stresses also remaining within allowable limits as per ASME PV Code.

Narendra K. Roy
Gramya Research Analysis Institute,
PO box 4016, Vadodara 390015, India
Website:

http://www.gramya.com

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http://www.charismaglobal.com

 

[roca]

Staying within allowable stress limits is not the only criteria for allowable deflection limits. Columns could deflect more than the 1 in 200 limit and still be within allowable stress limits.
Column deflection is mainly limited in order to ensure that the internals - (trays, distributor trays in packed columns, etc) funtion correctly and there is no bypassing between the gas going up the column and the liquid coming down it.

 

[bmoorthy]

I concur with Rocca.

Also check your foundation for the suitablity for the deflection condition.

The maximum static deflection allowed is generally L/200 when the vessel is subject to the design wind load. Where L is the height of the column. This is applicable for columns for L/D in excess of 10 or if the column is more than 30m High.
The above is the spec of Dupont. As far as UOP or EIL is concerned the allowable deflection is almost the same.

 

[johnnymist2003]

Hi all,

further to all of the above, don't forget about wind induced vibration if the thing is very tall and slender.
Sometimes this may be the criteria which will determine the thickneses of shell strakes - especially the ones at the bottom.
John