UL 58 Rated Tank - Need capacity

[RiverBeav]

I am a structural engineer by trade, but have a situation where a contractor needs to operate a heavy tracked equipment above a fuel tank buried in soil. All I have been told is that it is UL 58 rated, but this is likely an older fuel tank since the location that it was placed was built quite a long time ago (50's to 70's timeframe). The peak track pressure is somewhere in the 60 to 90 psi range on 2'-6" wide tracks, which is approximately 8500 psf to 13000 psf applied pressure above these tanks. The tank is buried a few feet into the soil, so that pressure will be reduced and equalized somewhat by the soil. Of course, we could do something to spread that load out some more above the ground, but it would still be a pretty large overburden pressure on top of one of these tanks, and exceeds typical truck loading effects.

I don't have a copy of UL 58, and it costs quite a bit to purchase. I suspect like any code, it just governs how you are supposed to design the tank, but may not provide minimum loads that tanks designed under its guidelines would be capable of supporting. How does that code handle the design of tanks for traffic loads?

Approving the operation of equipment above a tank like this is outside of my expertise. Just curious as to what is in the UL 58 code, how to know the capacity of tanks for supporting overburden loads, and what kind of mechanical engineer would be able to handle that analysis?

 

[IFRs]

You don't have enough information.
They have to tell you the size and orientation of the tank.
What edition of UL-58 was it built to?
You also need the kind of soil and an accurate distance to the tank - it it is packed gravel for 5 feet on either side that is much different than if it is soggy organics.
You also have no idea of the design or condition of the tank - is it single or double wall (probably single), is it of bolted, rivited, welded construction (probably welded), is it corroded and just about to leak (no way to know), does it leak already (possible but hard to determine), what pressure was it originally designed to (unknown without a nameplate), is it concrete encased (unlikely), does it matter if you crush it? etc.
Often buried tanks have gravel or crusher-run around them, can you dig a hole or drive a rod to explore?
You might be able to just lay 1" thick steel road plate over it and forget about it but more info would help you sleep at night.

 

[LittleInch]

That looks like a very heavy load overall and very high ground bearing pressures. Are they correct?

Buried circular tanks are quite strong, but with external load could collapse very suddenly.

There are a number of ways to calculate whether the tank is strong enough, but a large concrete or steel plate would help hugely.

Even timber bogmats would help, but IFRS is correct - you need much more information.

Do you still needs these tanks? If not fill them with concrete.

But those loads need checking as they total something like 350 to 400 tonnes or more depending on the track length

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

 

[HTURKAK]

My points are,

- If it was built quite a long time ago ( probably 60 yrs old ), IMO, the tanks should be abandoned. I have knowledge of some company standards (e.g ARAMCO standard ;Buried UST systems, in greater than 10 years service shall be renovated to meet the construction requirements of this standard.) If the subject tanks abandoned , filling with gravel could be an option .

- I have old copy of UL 58 . AFAIK, it refers ROARK'S formulas and provide thicknesses for various sizes for 5 ft overburden .

- If you can provide more details ( orientation, size , burial depth, secondary containment, wall thk., no. of stiffeners ..) you may get better responds..






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[RiverBeav]

Thanks for the feedback! This is a hospital site . . . the drill rig to drill a hole for a 7'-0" diameter pile is very heavy, I think around 250 to 300 kips. I will begin the process of getting more information on the tank. No real easy answer, but it does have a thick concrete pad above the tank that might be what allows work to occur above it. It could be a newer tank located in the older part of the hospital.

Thanks again!

 

[RiverBeav]

So I have some updates. I asked for more information about the tanks, and found out that they replaced the original tanks with more modern tanks (built around 2003). So these tanks seem like a standard design, labeled as a "permatank". It sounds like this tank design can be manufactured by anybody approved by the steel tank institute (and I found a few company names on the STI Website). The original manufacturer for these specific tanks is now out of business.

Just curious whether any of you are familiar with these tanks?