Design Analysis of Horizontal Tank 1

[David A]

Hello all,

This is my first time posting. I have been to the forums many times over the years, but never have I been this stumped. Hopefully someone has some experience with this design.

We are evaluating an existing tank for a client located in the bay area of California. The tank is a steel 2,500 gallon above ground tank containing vehicle fuel. It's a horizontally oriented, cylindrical tank and is constructed within a secondary containment/double wall enclosure. The tank base is a completely flat bottom. We have been tasked with evaluating the anchors and restraints for overturning and shear. We analyzed it at a rigid, non-structural component. The regulator has denied our calculations as deficient and states that we need to use ASCE 7, Chapter 15.7 for the basis of our analysis. I disagree with their code reference, as 15.7 is for design/analysis of tanks and vessels supported at the base, like a water storage reservoir or grain silo. They also want an analysis of the available freeboard and resultant force of the sloshing of the tank contents. The freeboard equations provided in Ch. 15.7 assume a vertically oriented structure with constant cross-sectional area with regards to the height of the contents. A horizontal cylinder has a varying cross-sectional area.

Here's my question: Is there a better reference or design guidance for horizontally oriented tanks? Am I off base here, or is the regulator incorrectly siting code?

Any help would be greatly appreciated.

 

[MJCronin]

A couple of things .....

1) I do not understand a "flat-bottomed" horizontal tank .... Is the axis of the tank vertical or horizontal ? If indeed this is a horizontal cylinder, why on earth would someone deliberately make seismic anchorage and gauging much more difficult ? ...... Pictures or sketches available, perhaps ???

2) If indeed the tank sits on its "flat-bottom" the design rules of API-650 may be much more appropriate. There is much more information on these fora and on the internet on developing anchor bolt loads and evaluating the effects of sloshing.

MJCronin
Sr. Process Engineer

 

[chicopee]

"...It's a horizontally oriented, cylindrical tank..." how can such tank have a flat bottom or does it have the shape similar to a Quonset hut? A sketch of the tank is appropriate.

 

[LittleInch]

Something like this?

All seems rather OTT for a 2500 gal tank inside a bunded area.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[David A]

Thank you for checking this out. The main storage tank is a horizontal cylindrical tank. It is built within a secondary containment out housing that creates the flat bottom. It's hard to even design the anchorage for for a horizontal tank with concrete or steel saddles. We have analyzed it a a rigid, non-building structure.

I'm not sure how to upload pictures on here, but this is a link to an identical tank. It's a UL 142 listed tank.

 

[LittleInch]

So the square sides enclose a cylindrical tank?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Bit of a strange thing to analyse alright.

If you get no real joy here, maybe try the storage tank engineering forum and refer back to this post.

I would have thought your worst case was half full for sloshing so why not do the numbers for a circular tank and see what happens.

Or just strap it down / drive in four posts around the sides and be done with it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SnTMan]

Kind of an interesting beast, doesn't look as if it is designed to be anchored. I don't see why a rigid, non-building approach is incorrect.

For interested parties, this is discussed in the Structural forum as well.

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[MJCronin]

UL-142 tanks are intended for inexpensive local storage of fuels and are marketed and sold for that purpose. They are very competitively priced and are sold as commodity items.

https://www.highlandtank.com/aboveground-horizontal-ul-142/

UL-142 tanks specifically are NOT TO BE SELECTED for transient events such as earthquakes or liquid sloshing.

If an experienced tank purchaser anticipates such events, he should have selected a tank SPECIFICALLY DESIGNED FOR SUCH EVENTS!!!

You can tell your MBA boss that a more robust tank design code such as API-650, API-620 or ASME VIII should have been specified. This is clearly addressed in the NFPA-30 fire protection standard.

The UL-142 Code is also quite clear on this point:

https://standardscatalog.ul.com/standards/en/standard_142

Section 1.6 These requirements do not cover special evaluations for resistance to hurricanes, tornadoes, earthquakes, floods, or other natural disasters; or resistance to vehicle impact.

You should also be aware of the fact that a New Design Standard from the STI has been developed that meets and exceeds the UL-142 requirements AND can be made suitable for seismic areas. The Tank Design Standard is F921 and is for double walled tanks.

http://www.ipstanks.com/files/IPS - F921 04.14.pdf

MJCronin
Sr. Process Engineer

 

[chicopee]

"... The tank base is a completely flat bottom..." This portion of your description is incorrect. I have seen and inspected such tank as the one shown in the picture of your second post and such tank is actually cylindrical with clearance between the cylindrical bottom and the flat bottom of the rectangular secondary containment. It is UL Inc. Listed tank probably labelled for flammable liquid storage. It is shop fabricated and the sloped steel plates are to keep storm water out of the tub. In all likelihood it has leak detection at the flat bottom of the tub. Get hold of the manufacturer whose name should be on the nameplate for any information requested by the regulator and that should save you some work.

 

[chicopee]

Here is a picture of the tank which I inspected over the years on an annual basis in MA as it is over 10,000 gallons.

 

[DriveMeNuts]

It looks like a regular cylindrical tank on saddles (not shown) with a square protective barrier welded to it afterwards. (Does the square barrier actually support the tank, or is it just clipped on?)
Perhaps, do a regular calculation of the cylindrical tank on its supports and completely ignore the square protective barrier.

 

[r6155]

Ask your client for the original design (new tank)

Regards
r6155