Tank Ring Walls

[OP1]

I have read a few threads about ring walls and have a different question.
First off, I am not an engineer. I work at a small power plant and we have a 26' x 26' water storage tank that sit atop a 4' ring wall. I noticed water leaking around one side of the base of tank. The ringwall was damaged slightly during the 6.5 San Simeon Earthquake back in 2004.
We filled the cracks in the foundation with an epoxy. The epoxy has since cracked. I have noticed that the concrete under this section of the tank is about 10 degrees hotter than the rest of the ring. Is this significant?
I believe the ring is 2' wide and has anchors to conform with Seismic zone 4.
We plan on going into the tank in May to inspect the floor. Is there anything else I should be concerned with? Is it possible that the leaking water is permeating into the concrete causing it to be hotter at that point?
Thanks for any replies.

 

[JedClampett]

A few questions:
You said the tank is 26' x 26'. Is it round or square?
What's in the tank? Is it plain water, cooling water, potable water, etc?
As far as the concrete around the damaged area being warmer, that's a real stumper. There's no reason that repaired concrete should be creating heat. If the liquid is warm inside, it might be closer to the exterior due to the cracks and locally warming it.

 

[OP1]

The tank is round. 26' diameter, 26' high.
The water is 180 degree "boiler feed" water.
Inside the ring is 95% compacted oil sand.

 

[JedClampett]

I forgot to ask if the tank is concrete or steel, but I think the answer is that it is leaking.

 

[OP1]

haha... yup it's leaking.
It is a steel welded tank. with a floor that is i believe 3/16

 

[JedClampett]

It's hard to tell how bad the damage is to the ring wall from your description. If it's settled or cracked, its movement would have to be pretty substantial to break the tank bottom. Steel stanks are pretty flexible. But it apparently did. Expect to find a seam that's leaking. Depending on the amount of separation, the fix might just involve rewelding the seam. Fixing the ring wall involves hiring someone to survey the damage and design a fix. The tank, while empty, might have to be lifted off the foundation and the subgrade replaced. During this time, the ring wall can be repaired.

 

[OP1]

The cracks to the outside wall were pretty visible at one time. The engineer that took a look at it said the epoxy should do the trick. But at that time i don't think any consideration was given as to weather the ringwall was damaged "under" the tank or weather or not the ringall damage put any undo stress on the tank itself. My other question would be How can I tell wheter or not The water IS indeed soaking into the the subgrade and what future effect that can have on the tank if the tank is just rewelded or repaired without looking at the subgrade. I know everything is cost related. If we can go another 15 years by just getting by with a tank weld then that will all play into the fix.
Thanks Again

 

[JedClampett]

There's an excellent chance that just welding the tank will get you by for quite a while. What's the downside? If the tank ruptures (worst case), are you out of business? Can you adjust operations so that you can bypass the tank? Is there a significant safety issue? This will enter into your evaluation.
From my previous life in the power plant business, I remember a lot of jerry rigged systems held together with baling wire and chewing gum.

 

[OP1]

Exactly. Chewing gum and Bailing wire.

Thanks for all your input Jed. I'll come back in and post later once we figure out where we want to go with it.