Structural Assessment for Storage Tanks

[leont]

I have a tank with a localized damage on lower shell course next to bottom – shell welding. Diameter= 40' and height= 60'. Nominal thickness 0.375" and the lower thickness on the area is 0.099". I know in API 653 there is information regarding Fitness for Service Assessment, but I believe I have to see this issue from the structural view point and to deem the shell as a column in order to look for when it can failure based on the minimum corroded thickness.

What is your experience working with similar cases, knowing internal pressure is not a concern?

Your help is highly appreciated.

 

[jte]

...deem the shell as a column...

And check it for Euler buckling?

...knowing internal pressure is not a concern

What do you suppose is causing the shell to rotate out at that pesky 90 deg joint to the annular ring? What is the internal pressure on the bottom of the shell?

jt

 

[JStephen]

Generally, compressive/column loading would not be a big issue for tanks unless subject to high seismic loading. Even then, very localized thin spots would likely not be an issue. Internal pressure/ hoop stress would be the main issue. That and leakage.

 

[leont]

Hi
Thanks jt and Jstephen,

Again

I have corrosion under insulation localized on such areas.
Calculations have done and I know it will not fail by internal pressure, but I would like to know when it would fail, since I have wall metal loss in more than 60%. These localized areas are located adjacent to Shell bottom welding joint. In some cases this weld joint is affected as well.
Just what I want is to know how I can assess such situation, deeming height and diameter of the tank. Since structural view point, how it is affected, how I can know stress on this critical areas. Please go over height and diameter of the tank.

Thanks a lot and have a great day

 

[jte]

You've already looked at API-653; you should move on to API-579-1 / ASME FFS-1 which will guide you on your fitness for service asessment.

jt