Storage tank double bottom corrosion 1

[Gonz7979]

Have an issue with a above ground storage tank that has a double bottom. During sandblasting to repaint the tank we found 2 hole in the shell of the double bottom. See picture. My thought is that this does not provide any structural support to the tank and is more of a containment for the sand/aggregate that is inside of the double bottom. So my question is do we need to do a weld repair on the shell, such as a lap patch or can we just seal it with some sort of epoxy.

 

[LittleInch]

From one photo with no other info it's not possible to say, but holes in tanks are not a good idea and simply to stuff some epoxy in doesn't look like a sound repair to me.

How did such a big hole develop - you need to find the cause.

Any drawings / sketch of this area?

Is this the inside or outside?

If you have a leak in the inner tank then you now only have a single skin tank....

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

 

[IFRs]

It's really hard to tell what this is a picture of. But if it is the original shell below the secondary (upper) bottom, often called the "dead shell" then it does supply structural support for the tank shell and it must be aligned with the rest of the tank shell above the secondary bottom. I'd seal weld a section of rolled plate of equal thickness spanning that area, make sure the dead shell is seal welded to the underside of the upper bottom all around and check the integrity of the dead shell all around. This section of shell plate and the old lower bottom are now part of the foundation of the tank and must be able to transmit all loads from the tank above it to the foundation under it (dead, live, product, hydrotest, wind, seismic, thermal, etc.). Also read LittleInch's post and see if you can answer their questions...

 

[Dhurjati Sen]

Is the tank under shutdown?

Won't you carry out MFL of the bottom plate to assess corrosion (both sides)?

Your answer could be there.

DHURJATI SEN
Kolkata, India

 

[zelgar]

If this tank is a double-walled tank and one of the walls(bottom) of the tank has a hole, you no longer have a double-walled tank. I would look to API 653 to look at possible repair requirements for this tank. Note: If the double-wall is a requirement to meet secondary containment requirements for the stored material, the tank is not in compliance until the hole is repaired. You might need to take the tank out of service until repairs are complete.