Chime plate distortion

[hamdykhalaf]

The crude oil storage tank suffer from external corrosion ( heavy corrosion and even a holes ) in the chime plate, some portion suffer from distortion ( until the toe of the shell to bottom weld )
the internal annular plate is not corrded since it was repaired by an internal annular plate welded over the original plate

what is the solution to repair the external chime ?

 

[IFRs]

Your first 7 pictures show a perfectly good annular plate. For the rest of the pictures it is impossible to tell where they were taken, please help.

If the internal plate that was welded over the original did not extend through the tank shell, it was ill-advised and a very poor detail, not in accordance with API. If this is truly the case, then you should remove and replace the entire annular plate.

 

[hamdykhalaf]

Thank you for your reply

The others photos was taken under the annular plate after removal of the concrete ,it can confirm the corrosion of the old internal annular plate
I agree about the illnes of the repair method done over the internal annular plate ( fillet welded with the shell).
I attached another photos that show the distotion of the chime.the photos N° 6 and 7 shows a holes near the shell to bottom weld,( this holes was detected in many areas )

Thank you in advance about your help

 

[amos4]

Agreed with IFRs
It was a bad idea to repair only the "internal annular plate". As an aftermath of the bad idea, you are now asking for solution to repair only the "external".

I would say, perform a thickness check on the shell (1st Course) periphery, particularly the HAZ, to determine your corrosion rate. If the shell plates are still "healthy", you can look at tank jacking to replace the entire annular plate (from internal extending out to external), employ necessary NDE and put the tank on hydrotest before service.

 

[Duwe6]

Gotta agree with amos4; have a Tank Erection & Repair company cut the chime weld at the top toe and slot in a new annular ring. It can be done in sections, and grout the gap between the new ring and the old concrete ringwall. The grouting will allow the tank nozzles to remain at their current elevation without cutting them out and rewelding them.

Consider thickening the new ring, as you now have a corrosion history and can calculate the corrosion rate. Add enough thickness to give this tank at least 50 more years of 'useful life'.

 

[IFRs]

Chime weld must be cut at least 1/2" [13mm] above the toe of the corner weld if you intend to comply with API 653