Tank shell evaluation according to API 653

[Andres Romero]

We have a tank that has a strip of corrosion around the perimeter of the first course.

The corrosion stripe is produced by corrosion under insulation (CUI).

The corrosion strip has a height of approximately 100 mm and is located at the bottom of the first course.

My question is how to evaluate this corrosion.

The thicknesses must be averaged as stated in paragraph 4.3.2.1 of API 653 or I must consider it as generalized corrosion and evaluate it according to paragraph 4.3.3.1 b) of API 653.

I don't like the idea of averaging the thicknesses since it is a low strip along the entire perimeter, the result of averaging the thicknesses is very high.

I attach photos of the corroded area.

Kind regards

Hello everyone, I have a question when evaluating corrosion in the shell of a tank.

 

[Dhurjati Sen]

The tank is in service, right?
Clean the surface by buffing, apply a coat of zinc epoxy and put back the insulation properly.
Once you remove the corrosion agent, you need not worry about that location till the next shutdown.
Include this issue in the job list for the next shutdown where you carry out external weld build up and restore the original thickness.

DHURJATI SEN
Kolkata, India

 

[zelgar]

If the green liquid shown in the pictures is the material stored in the tank, I wouldn't be worried about the tmin, but take the tank immediately out of service.

 

[Andres Romero]

Hello, the green liquid is the couplant used to measure thickness.