tank shield design to contain pinhole leaks?

[leakyseal]

Folks,

I've poked around here quite a bit with no luck so hopefully the answer is not staring me in the face.

We have a chemical storage tank inside a containment bund of sufficient volume to hold 150% of the tank's volume, as one may expect. The question has arisen, what if there is a pinhole leak at some elevation above the bund wall, such that the material could arc over the wall (thanks to Torricelli) and we then have an environmental release.

A few folks around here claim to have anecdotal experience with building a "splash wall", a thin shield of material standing off the tank wall by virtue of some sort of stud pattern, such that an internal pinhole leak would impinge on the shield and run down to the interior of the containment.

Anyone have any experience with this kind of design or can suggest a standard or code of practice? I'm durned if I can find such so far. (note also that we cannot easily extend the footprint of the containment to capture the arc, due to real estate and the absurd cost of concrete at this remote site).

Thanks in advance, Leaky

 

[IFRs]

Is the containment wall really that close so that liquid could squirt over it?

 

[leakyseal]

IFRs: yes, preliminary estimates indicate that this is the case. the tank is quite tall and relatively narrow for remote fabrication / road transport reasons.

 

[IFRs]

I don't think the answer is easy. From the estimates, how high or wide would the shield wall have to be? You could make a leap of faith and say that the leak would occur at a weld seam, and weld thin shields over the weld seams. I believe that NFPA says that the containment wall must be 5 feet or more from the tank. Is yours 5 feet away? Some geometry might help...

 

[JStephen]

The insulation people normally put an aluminum jacket over the insulation- just do that, but omit the insulation. Or possibly drape fabric down the tank. Sounds like overkill in either case, though.

 

[leakyseal]

To explain further motivation for the question, the relevant gov't agency standard says "The perpendicular distance between from the tank face to the top of the inside face of the containment shall be min. 1/2 the height above the top of the containment wall."

We cannot provide this. Hence, the pinhole barrier concept is being floated.

JStephen, we have used that approach before but this tank is not intended to be insulated and we feel that the distance between insulation support risers (in my experience, rings of angle iron) to support sheet cladding alone is insufficient. [that said, it may be cheaper to spec standard rigid insulation and be done with it than try to finesse this alternative design...]

 

[IFRs]

Which government agency is this? Which country / state / local?

 

[leakyseal]

IFRs: Ontario Ministry of Environment. Revised Chem Storage COP 2007 (or thereabouts, I don't have it in front of me).

 

[IFRs]

Thanks. I was worried I would have to deal with that in the US. Whew!

 

[leakyseal]

I had been wondering if USEPA had something similar and was going to check this morning.

This installation is actually in Newfoundland but we've been using the Ontario rules as a starting point...

 

[zelgar]

Looks like the regulation is here:

http://www.ene.gov.on.ca/envision/env_reg/er/documents/2007/Storage Guidelines.pdf

Middle of page 18

"Containment systems should be designed such that the horizontal trajectory of a potential leak from a tank will be confined within the impoundment. As a guide, the perpendicular distance from the tank face to the top of the inside face of any containment should be a minimum of half the height of the tank above the top of the containment wall. In cases involving very high risk of loss or damage, calculations should be made to determine the required distance. For areas with restricted space, a higher containment wall or shields placed in areas of risk should be considered. The secondary containment system should isolate and protect the tank from vehicular traffic, fire, and spills of incompatible materials that might occur in adjacent storage or work areas."

 

[IFRs]

Ahhh - yes I see. Still looking for a US equivalent?

 

[leakyseal]

Truth be told, what I'm looking for is a fabrication detail or code of practice (or external anecdotal evidence) for a splash wall built on standoffs from the tank wall. I can devise one but would prefer not to reinvent the wheel if possible.

 

[zelgar]

Currently, I'm not aware of any corresponding regulation under 40 CFR 264 or 265 regulations for hazardous waste tanks, nor does Indiana have this requirement (I don't know about any other State).