Atmospheric Storagge Tank Bottom Plate Assessment

[shehzad305]

Greetings!

This is to seek your advice on below issue in Atmospheric Storagge Tank Bottom Plate.

It is very common in the indusrty that underside/soil side corrosion happens due to poor sealant management. This causes corrosion of bottom/annular plate outer projection ring at first and penetrates inwards in the critical zone of tank bottom and so on.

Once corrosion is revelaed on outer projection ring by Ultrasonic thickness survery, we do Short Range UT to check the thickness of bottom/annular plate in the critical zone (1meter inwards from shell).

Kindly help me to understand what will happen if some length (2 to 3 meters) of outer projection ring is very low thickness i.e. less than 2.54mm. OR incase the shell to outer projection ring weld gets deteriorated.

 

[HTURKAK]

Apparently you need to conduct assessment study for corrosion and fitness for service. You did not mention if the corrosion is pitting or general corrosion.

You may look API 653 ,

- 4.4.5 Minimum Thickness for Tank Bottom Plate,
- 4.4.6 Minimum Thickness for Annular Plate Ring
- 4.4.6.1 Due to strength requirements, the minimum thickness of annular plate ring is usually greater than
0.10 in. Isolated pitting will not appreciably affect the strength of the plate. Unless a stress analysis is performed,
the annular plate thickness shall be in accordance with 4.4.6.2 or 4.4.6.3, as applicable

If you provide more detailed info ( tank size, service, bottom and first course shell as constructed thick, first course stress,how old the tank...) you may get better responds..