AST Forum
Here I have a 290 gallon steel AST used to store and dispense gasoline. There are no visible markings or labels left on the tank. Is it possible to determine whether it is double-walled just from observing the vents on the tank? What would be your recommended approach to determining whether it is double or single walled?
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It is very-very unlikely that your 290 gallon -probably 300 gallon tank- steel AST is double walled with no nameplate which is welded to the tank. I am presuming it is a horizontal AST on a framed skid?
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Well it is a pressure vessel that seems to have repurposed for a ast.
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This is a Single Wall Tank. There would be no point in having ALL the piping connections coming from/through the outer tank. If you require proof: measure and calculate the capacity, fill and compare the difference.
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Dunedin - all the nozzles have to come out through the outer wall...yes???
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David not necessary. The nozzles on the inner tank should terminate in the space between the inner and outer tank and be accessed through a hatch on top of the outer tank. The exception would be the bottom outlet which would be the only pipe coming through the space. The principal of a double tank is that the outer tank protects the inner tank in the event of say a projectile hitting the outer tank. However if the outer tank contains all the nozzles then there is a danger that damage to the outer tank will result in the nozzles tearing away from the inner tank and defeating the purpose.
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If it is a double-wall tank, at least one of the vents should be for the space between the tanks and at least one should be to the inner tank. You should be able to detect this. Put air or smoke, etc into each opening and record which of the other openings pass air or smoke, etc. Make a drawing and put the data on it with arrows.
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This tank may be classified as an AST, but it clearly does not fit the criteria for being an AST. I am sure I am not the only one that has seen this issue at plants where they call it an AST because it is now operating under atmospheric or very low pressure. The design does not comply to the Scope in either 653 or 650. I know, owners can call them whatever they want, but this is one of those items that kind of bothers me. Sort of silly, but thats me...
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Easiest way is to remove the two mushroom vents from the fittings on top of the tank and visually look inside. If both of those vents reveal the contents in the primary tank, then you have a single wall.Fitting with Pump is into primary tank.Fitting with Flip Top Cap is probably into the primary tank. Open and look inside to confirmFitting with the gauge is most likely for primary tank fuel level. It could be, but I doubt it is, a monitor pipe for leak gauge that would be for the outer tank only in a double wall setup.Darren Sanderson,Hall Tank CompanyNorth Little Rock, Arkansas
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