Dear all, I have some questions 1

[Chrysalidis Alexandros]

Dear all,

I have some questions regarding the replacement of an API 650 Crude oil storage tank bottom by leaving in place the existing old tank bottom and install a new bottom above the old. Except the shell sloting method what other methods exist?
If support clamps (commonly called dogs or C-bars) is not going to be used and the new annular plates will be installed from the outside of the tank what is the minimum required cutting length of the shell in order to install one annular plate?

Thank you in advance!

 

[Dhurjati Sen]

Dear Chrysalidis Alexandros,

Hydraulic jacking of the shell is another method where you lift up the entire tank.

Your second question does not arise if you use this method.

If you use the shell slotting method, check API 653 for the length of shell you need to cut to insert the plates.

Regards.



DHURJATI SEN
Kolkata, India

 

[Chrysalidis Alexandros]

Dear Mr. Dhurjati Sen,

Thank you very much for your kind reply.
We are trying to avoid the shell slotting method and the hydraulic jacking due to high cost and work effort.
We would like to insert and install the annular plates from the outside of the tank. Does the API refer to a method like this? What we are most interested in is the minimum permissible cut length before installing any annular plate.

Kind Regards.

 

[LittleInch]

Got a drawing?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IFRs]

API 653 is silent on this question. However, annular plates are commonly 20 feet long +/- and you can probably make a 1/2" slot starting 1/2" above the corner weld for 21 feet, slide an annular plate in and proceed around the tank. The worst that happens is your slot closes up a little from the weight above but depending on the shell thickness and height this may not happen. If you were concerned about this, cut the annular plates in half, to be only 10 feet wide, or even 8 feet wide. You may experience bottom side corrosion from the old bottom plates touching the new. Are you going to remove the old bottom? Does the old bottom have holes that will allow moisture in?

 

[LittleInch]

Are you the owner or designer?

Sounds like you need to talk properly to an experienced tank repair company to generate some ideas and options.

These guys have seen and done it many times more than us.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Chrysalidis Alexandros]

Dear all,

Thank you very much for your kind answers, I appreciate it a lot.
The old bottom is not going to be replaced. It will stay there. A perimeter layer of sand or gravel or concrete of 3 in minimum thickness will fill the space between the old and the new bottom as it is required by the API RP 575. Also anodes will be placed between the old and new bottom to avoid galvanic corrosion. Now the annular plates is usually as you said 20 +/- feet long. Is it possible a slot (cut on the shell) of about 21 +/- feet long to be opened, next install and welding of one annular plate and go to the next one (same process) until we reach the hole perimeter? (We speak for a tank with a diameter of about 70m.)

Thank you in advance,
Kind regards.

 

[IFRs]

Your question was:
"If support clamps (commonly called dogs or C-bars) is not going to be used and the new annular plates will be installed from the outside of the tank what is the minimum required cutting length of the shell in order to install one annular plate?'

The easy answer is:
In lieu of the support clamps leave a 12" section of shell unslotted in the same locations you would have put the support clamps.

One method of installing might be:
As you install the annular plate, if there is a significant gap between the new annular plate and the tank shell above the annular plate, use wedges to support the tank shell at the annular plate, then cut out the next supporting section of shell and continue around. At some point you'll need to remove the wedges. If there is no significant gap between the annular plate and the tank shell above it, wedges would be not needed and the tank will just settle down on to the annular plate once enough shell support pieces were removed. This action of the shell lowering down by self weight is similar but not exactly the same as removing the support clamps one by one and seeing the same action.

What is a "significant gap" - that is for a tank engineer to help you with.

You don't explain why you don't want to use the simplest, least expensive, proven method of putting in a secondary bottom (using support clamps), but that is for another conversation.

 

[Chrysalidis Alexandros]

Dear Mr.

Thank you very much for your suggestion.
At this stage of the project we just need to know what options we have. After we will be able to evaluate all of them and choose the most efficient according to our capabilities.

Thank you a lot,
Kind regards.

 

[IFRs]

Your best source for options are qualified contractors who do this for a living.