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Internal Coating of Storage Tank

Internal Coating of Storage Tank

Internal Coating of Storage Tank

I am working on a new refinery project in the middle-east where for internal coating application contractor is seeking to cut open the shell approximately 3.5 m x 3 m to allow easy entry of coating application equipment such as a man-lift. The tank has already been hydro-tested. Contractor proposes to re-install the shell and carry out radiography on the new welds (no hydro-test, though). To my understanding no significant welding should be carried out on a hydro-tested tank. While in Canada, I never received any such requests from the contractors although I awarded such tanks to many Alberta contractors. It is quite possible that such requests never reached the home office, so I never came to know about it.

Is it a common practice to make large openings in the shell for coating application? Has anyone allowed such deviation from API 650?

RE: Internal Coating of Storage Tank

IMHO, the installation and application of the coatings system should have been considered at time of tank design.

Suddenly "discovering" that access to the interior is required, a large hatch must be cut from a newly hydrotested shell is the hallmark of bad management .......

These doors have been cut into tanks before .API-653 contains rules and limitations on the size and radius of the door

You will not have an API-650 certified tank after the door is cut and then rewelded ..... Is that acceptable with the owner ?

Full sized manlifts are nice, but they are not the only way to gain access to the tank interior.

Movable scaffolding and new "narrow" manlifts have been used for painting.

The tank should have ;been configured with multiple large manways on the shell AS WELL AS A SQUARE ROOF ACCESS FOR INSERTING OF EQUIPMENT.


Sr. Process Engineer

RE: Internal Coating of Storage Tank

Common practice is to leave a door sheet unwelded in the tank if that kind of access is required on a new tank. Of course, that would imply that hydrotesting is done after coating, which is allowable, but not always considered acceptable.
Cutting a door sheet as described is common on existing tanks, and covered in API-653, seldom done on new tanks due to having better options.

RE: Internal Coating of Storage Tank

Thank you, MJCronin and JStephen for your prompt replies.

Really appreciate it.

Thanks again.


RE: Internal Coating of Storage Tank

The tank has been hydrotested so the foundation and shell have passed.
It is an API 650 tank.
API 653 has guidance for removing and installing a door sheet without a hydrotest being required.
Usually API 653 comes into effect after the tank is put in service, but I don't really see the harm in doing this work on a new tank.
If you don't want to cut into the shell, cut a hole in the roof and place the equipment inside with a crane.

RE: Internal Coating of Storage Tank

Thank you IFRs.

I am discussing with the client and will most probably allow cutting a door-sheet.


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