Is there an acceptable roof distortion amount for atmos tanks?

[jeevesme]

I cannot find anything in the build, repair,or inspection codes that address roof distortion on atmos. tanks. I have a few tanks that have some buckling in the roofs. They are all fixed roofs. What would be considered okay, and what would deem it not fit for service? Is there a standard or good practice?

 

[IFRs]

If they will make ponds where water will collect you may want to consider fixing them, otherwise, I think it is a big who cares?

 

[chicopee]

Or apply a thicker coat of paint where pooling occurs.

 

[DSB123]

chicopee,
Won't that make the buckling worse with the weight of the additional thickness of paint - lol

 

[LittleInch]

That's the thing about roofs on atmospheric tanks - they are there basically to stop the rain getting in so as long as they continue to do that then they are OK. Only if the walls are damaged as a result or the roof buckles due to wall damage / movement does it need to be a concern. There is a difference between distortion and buckling. One way maybe is to look at the maximum deformation from flat over the distance of the distortion. If this is more than 10% depth to length then you might have a problem, anything less than that and it should be Ok, especially if it is a gentle curve.

You could also apply the infamous FGT or Fat Guy Test. If you get one of your more stoutly built colleagues (or may be two of them) to stand on the up raised bit and it flexes down then it's OK. If it stays there then think about replacing it or strengthening it...

I don't think there are any hard and fast rules about this as one persons "buckling" is another's small deflection. The roof structure is almost irrelevant to the safety or strength of the tank, more about the safety of anyone walking on the roof.

An experienced tank repair company would probably give you an inspection report, especially if you paid them, but bear in mind they make money by repairing tanks so...., but at least you would have a written report.

Any pictures for people to comment on would probably generate some interest, i.e. whether people think it's a "buckle" and needs repair or not.

My motto: Learn something new every day

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

 

[Duwe6]

"If they will make ponds where water will collect you may want to consider fixing them, . . "
My rule-of-thumb is if there is moss and/or algae growing, recommend a repair or improved paint. Otherwise it is cosmetic, and upper management does not look at the tank roofs much. MUCH better things to spend the maint. & repair budget on than wrinkled roofs.

 

[IFRs]

I've see grass and small trees growing. Ice ponds are a safety issue if in the walking path to a gauge hatch or other inspection point. LittleInch devoted much more time for this and has pretty much nailed it. Give him a star!

 

[JStephen]

Note that some of these buckles or waves can vary depending on the temperature, etc. If the columns under the roof settle, the roof will be looser.

 

[zelgar]

Since it seems like minor distortion may not be a structural problem, but what caused the distortion may be relavent. Was the distortion caused by pressure build-up or a vacuum within the tank? Are the pressure relief valves working properly or were they properly sized when the tank was installed? These items may be more relevant than a little cosmetic damage to the roof of the tank.

 

[IFRs]

zelgar has a great point. I ran into a line of tanks that had various degree of roof buckling. The foundations were at fault, the inner columns had settled, the floor was about to break. It may have been due to an underground stream becoming active following a flood.