Repair of Damaged Umbrella Style Roof

[pbc825]

Does anyone have experience repairing umbrella style roofs on API storage tanks? If so, has anyone been a part of a repair in which the roof was damaged by vacuum pressure (i.e. buckled from the central vent to the wall) and repaired by pressurizing the tank to "pop out" the damage? Is it possible, or has it been done before? What potential problems might a contractor need to look out for? My primary concerns are as follows:

1) Will there be yield lines or local defects to contend with following the repair?
2) Will the dynamic nature of the repair risk rupture at the knuckle region (or any other areas)?

 

[fegenbush]

I have seen this done before. I cannot say that I recommend it, especially so for the inexperienced. It is not a viable option if the material is kinked or creased (significant plastic bending behavior).

 

[pbc825]

Thank you for the quick reply and your help fegenbush.

I'm glad to hear it's been done before. I am inexperienced with it; therefore, I'm not in charge of the repair nor am I certifying following completion.

 

[MJCronin]

Please respect us....

Complete this thread and let us know about your experiences and final solution.

I am particularly interested in the design pressure of your tank and the proposed "pop-out pressure".

Also, how is your tank anchored ?.... Do you expect any damage to the anchor bolts ?

Will you perform this operation with a full/empty/partially full tank ?

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[Compositepro]

If you do perform this proceedure, do not use air pressure, only water pressure. And avoid any air pockets shed air can compress and store energy that can be dangerously released suddenly.

 

[pbc825]

MJCronin, I didn't mean to be disrespectful. As we're still in the planning stages there have been no final solutions or real experience gained yet. I'll be sure to update the thread once the repair is complete.

The design and pop out pressures will be evaluated in the as-built condition. The tank is anchored, and analysis of the anchor bolts/chairs will be evaluated prior to the repair.

To answer Compositepro and MJCronin, the tank will be filled to the roof level with water to reduce the stored energy from air.

 

[Compositepro]

I'm not sure you get how dangerous compressed air can be in this situation. With air pressure once things start to move, they will move very fast and you will have no control over how much. Water will move things slowly and controllably. You must take great care that there isn't any pressurized air in this tank during such a procedure.

 

[fegenbush]

Compisitepro,

API 650 tanks are not generally designed such that their roofs are intended to contain water. It may be that doing so would overstress the shell. Additionally, it is common practice to raise roofs on large diameter tanks using air pressure, which illustrates that there are some major differences between storage tanks and pressure vessels.

Obviously, safety is paramount in these scenarios. This is why I advised against it, especially for the inexperienced.

 

[JStephen]

My guess is, you can pop a roof back up with air or water pressure, but it'll still have creases.

Something that is not clear is the reference to the knuckle region. Knuckles are used for cosmetic effect on water tanks, normally not on industrial tanks. On industrial tanks, the main application would be on a pressurized roof, but you don't normally use umbrellas for pressurized applications. Is this perhaps a dome roof rather than an umbrella?

 

[pbc825]

If the roof will support water on it then likely water will be used to push as it can be done in a much safer fashion as we all agree.

As one would need to pressurize the roof to push out the dent, the joint between wall and roof (or knuckle region as I've referred to it in the first post) is subject to compression. Further, if the roof, "snaps" back into place this would further increase the compression and potentially rupture as a frangible roof would. But the details and numbers will be more telling.

 

[jtseng123]

This is API 650 tank, not taking much pressure. How can you be sure to pop out roof before popping out shell and floor ?