Annular bottom plate replacement 4

[alienitmeca]

Hello

this is my first time repairing a fire water open top storage tank designed according to API 650, date of fabrication is 1987, this tank suffers from corrosion in some of the annular bottom plates (according to the inspection report, 02 annular plates are set to be changed). in order to do that , i am going to use plasma cutting technique to remove the plates. Once these plates are removed and before welding the new ones, the tank shell may suffer buckling due to its weight.

I don't have a specific question, but looking for recommendations and comments

all feedback is always welcome

thank you in advance

 

[bimr]

In tank repairs, temporary supports and reinforcement are tack welded onto the existing tank to secure the tank in place. Buckled components would have to be replaced.

Perhaps you should make a call to an experienced tank fabricator.

 

[alienitmeca]

Bimr,

thank you for your prompt reply, i am considering temprary support with cylinders to keep the week part of the tank from buckling, but as i said, i am looking for all sorts of feedback, it can only help

thank you in advance

 

[bimr]

Here is an image that shows how a tank bottom is replaced. An automatic machine cuts out the bottom while the tank is supported on temporary clips. This allows a new tank bottom to be slid in under the cut.

 

[alienitmeca]

bimr

i feel very excited about the solution that you suggested, but i did not fully understand it, i would like to know more about it, could you please explain more

looking forward to receiving your reply

thank you in advance

best regards

 

[bimr]

Clips are welded around the entire tank circumference. A tracked cutter inside the tank then cuts the tank walls so that the tank bottom can be replaced.

Not sure what you are doing with your tank. I just posted this image to provide a concept for tank repair.

 

[IFRs]

Depending on your tank diameter, height and shell thickness, I might not be too concerned about it buckling. It may support its own weight and depending on how much you intend to slot, just leaving 2" of shell every 10 feet or so may be enough to keep it from any distortion. However, I don't think you can easily replace just two annular plates. If you are repairing to API 653, you need to cut 1/2" above the corner weld. What then??? I guess you "could" grout under the plate and weld the the new plate to the shell...(maybe not?) If you intend to replace the entire annular plate: (1) why is there an annular plate? If not required by API 650 your life may become easier. If you don't want to go there, (2) check if the annular plate to annular plate seams are butt-welded and note the more extensive NDE for butt-welded annular plate seams. The C-Clip shown by Bimr is standard tank repair method, assuming you are slotting the entire shell, adding an entire new second bottom above the first with some material between them ( sand, concrete, wool, grating, etc ), possibly with cathodic protection embedded in the sand, leak detection grooves and telltale ports, etc. However, this is a fire water tank. Secondary bottoms are usually not needed for containment. I suggest that your best option may be to make a 1/2" to 3/4" slot around the entire tank starting 1/2" above the corner weld and slip in a complete ring of 3/8" annular plates lapped on top of the existing bottom. Leave a 2" to 3" section of shell every 10 feet or so, when you place the annular plate in, wedge it up to the tank shell. Perform butt welds and NDE outside the tank by assembling 2 or 3 plates at a time. Remove the wedges and the shell tabs as you go. The tank will drop down the small amount, usually with no ill effects. Weld the new annular plate to the dead shell to prevent moisture from getting in and stabilizing the tank. Be prepared to deal with some (usually minor) piping issues as the tank settles onto the new annular plate.

 

[alienitmeca]

IFRs, bimr

thank you both for your prompt and informative replies, i will be proposing this to my coworkers, i will keep you updated

thank you very much

 

[IFRs]

If you agree that bimr had a great answer for you, reward him with a star

 

[alienitmeca]

IFRs, both of your answers were very helpful, thank you