Partially Buried API 650 Tank

[PEStructural]

I was wondering how I go about designing a partially buried welded steel tank. I can't find any reference in API 650 regarding this. I can perform a finite element analysis to determine the stresses, but what allowable do I use? Anyone know of any references? I've designed 100's of Aboveground Storage Tanks, but partially buried is a first for me.

Thanks in advance.

 

[JACKSTAN]

You always can determine allowable stresses using max temperature of heating part (e.g. temp. of heating oil included in coil or in jacket). I thing that probably this answer is not satisfactory for you.

 

[JStephen]

Treat it as an external pressure problem- similar to what is done with wind loading.

Is it actually an oil tank? If so, highly recommend not partially burying it, due to inspection difficulties.

 

[Flareman]

Just my thoughts but ..

Wouldn't you use the same allowables as for any tank, above ground or buried for both internal AND external pressure design ?
Soil pressures are well documented or you could ask for advice at the Civil Engineers forum.

I would have thought the issue to be more one of what corrosion allowance to select and how to protect the tank once it's buried. For that, try the Corrosion engineering forum.

David

 

[JoeTank]

If it's buried to a uniform depth all around, then treat it as an external pressure varying from zero at the ground level, increasing linearly to the bottom of the tank. Stiffeners will likely be required. API-650 does not currently address external pressure (vacuum), but will do so in the next few years. An agenda item is now on its way thru the committee procedures, but will not be avaiolable to help you on this one.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[PEStructural]

Steve,

FYI, I spoke to John Lieb from your company who authored the future Appendix V in API 650. He said that the appendix would not apply for buried tanks because it is only meant to address uniform pressures (not linearly varying pressures like soil).

What I ended up doing is using a Roark's formula (5th Edition), Table 35, Case 19b. which is the Formulas For Elastic Stability of Plates and Shells. This allowed me to back-calculate the allowable height between stiffeners given a certain soil pressure.

I compared the values to AWWA D100's wind girder calc and calculated that D100's equations are based on a factor of safety of 1.96 compared to Roark's formulas. I chose a factor of saftey of 2.00 and off I went.

 

[JoeTank]

Yes, the API and AWWA approaches use uniform pressures. If one compares a linearly varying pressure with and equivalent uniform pressure it shows that you would need to use approx the average pressure over the stiffened span. Actually it ends up slightly more than the average pressure, so I normally use 1.25 times the average pressure.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com