Bottom projection of a API650 tank
2

Question

Bottom projection of a API650 tank

tankinspector88 (Mechanical)

(OP)

31 Jul 24 21:52

I have a tank with the bottom projection corroded in the whole perimeter.
As you guys can see in the pictures, a lot of areas below the retirement limits.

API653 says:
4.4.5.7 Unless a stress analysis is performed that considers future corrosion until the time it can be inspected,
repaired, or replaced, the following criteria applies:
— the thickness of the projection of the bottom plate beyond the shell as measured at the toe of the outside bottomto-shell fillet weld shall not be less than 2.5 mm (0.10 in.), and
— the projection of the bottom plate beyond the outside toe of the shell-to-bottom weld shall be at least 10 mm (3/8 in.).

This stress analysis is just a finite element method (FEM) or is something more specific?
Anyone who already hired this analysis can share some results?

JStephen (Mechanical) · Answer 1 · 2024-07-31 23:39:57

From reading that, I would say it could be FEM or could be shell/plate analysis methods.
If you could exactly duplicate the corroded geometry in FEM, you'd theoretically get very good stress values. But in reality, I think you'd be assuming minimum values of shell and bottom thickness amd bottom extension and checking stress on that basis.

IFRs (Petroleum) · Answer 2 · 2024-08-04 11:34:23

It's time to repair or replace. How many inspections did this tank "pass" before it got to this point? Clearly it was painted recently, must have been after an inspection. This type of corrosion does not happen overnight! No inspections? Even worse! Is the owner shirking their duties and putting the public at risk? Unacceptable. Calculate all you want and then stand in front of a judge telling them why you did not repair or replace but instead let the tank leak all over the place, potentially causing a public catastrophe. Setup a system for periodic inspections and then follow it. Large storage tanks are not just cute cans storing stuff that makes the owner money, they are large capital equipment and a heavy responsibility that needs to be taken seriously.

tankinspector88 (Mechanical) · Answer 3 · 2024-08-07 16:56:29

Quote (IFRs)
It's time to repair or replace. How many inspections did this tank "pass" before it got to this point? Clearly it was painted recently, must have been after an inspection. This type of corrosion does not happen overnight! No inspections? Even worse! Is the owner shirking their duties and putting the public at risk? Unacceptable. Calculate all you want and then stand in front of a judge telling them why you did not repair or replace but instead let the tank leak all over the place, potentially causing a public catastrophe. Setup a system for periodic inspections and then follow it. Large storage tanks are not just cute cans storing stuff that makes the owner money, they are large capital equipment and a heavy responsibility that needs to be taken seriously.

I convinced them to carry out the repair.
A ring of annular plates will be installed.

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Bottom projection of a API650 tank
2