API 653 What to do When Tank Exceeds Out of Plumb

[coastalforu]

Hi folks. What are you to do when a tank exceeds the Out of Plumb measurement per API 653of 5"??? This is a 70 ft diameter x 40 ft high tank, leaning 20" on a clay soil. HELP!!!
Is there a requirement to relevel?

 

[JStephen]

API-653-10.5.2.1 gives a plumbness tolerance of 5". That is for a newly reconstructed tank, and is not a tolerance on an existing operating tank.

Refer to API-653-4.1, "an evaluation shall be made to determine its suitability for continued use".
See Annex B for more information on settlement and evaluation of settlement.

 

[IFRs]

You have several issues. Why is it leaning? Will it get worse? How will it affect your piping and floating roof (if any)? How long did it take to get to this condition? Usually leaning tanks have dents that can impeed an IFR.

 

[coastalforu]

There are 4 tanks placed 6 feet apart on clay soil 45 years ago. No foundation. They were filled with water and sunk 1 ft. This was the "expected settlement. When filled with a product 1.5 times as heavy, they began to sink and tilt in toward each other several inches. Tanks were drained and mud was pumped under the center to re-level them. A slight heave up was left in the center thinking this would settle out. When tanks were refilled, they began to tilt AWAY from each other. Tanks were emptied to the 50% mark which slowed this down. The tanks have continued to settle into the alluvial clay soil approx. 4 1/2 feet over 45 years and tilt approx. 1/4" per 4 years.

 

[LittleInch]

That is some flexible piping you must have or does that get modified every year or so?

Are all the manholes submerged?

It would be great to see a photo of this as 4 1/2 feet just sounds unreal....

If it contains anything hazardous or flammable then it definitely needs re-building IMO, but otherwise?? Tank would probably be showing signs of distress if it was in a really bad way so it might have some life left in it, but a properly supported raft foundation sounds like a good plan next time.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

One solution would be to empty one tank [at least down to a few inches of 'heel' liquid remaining], and then "Mud Jack" the tank back to a sembalance of level. Mud Jacking is done with structural grout, and could be done with a mix with enough strength to act as a foundation slab for that tank.

Refill with the S.G 1.5 material and measure further settlement, and use that measurement to compensate on the second tank being mud jacked. Rinse & repeat.