API 650 Tanks-Corrosion of Annular Plate

[nrp12345]

We have 2 nos 20 Mtr dia Naphtha Storage tanks designed as per API650. These were installed in 1965-66. Till about two years ago we were monitoring corrosion of the external portion of the bottom annular plate. The tanks were moth balled for two years and attempts are now being made to rehabilitate the tanks. We observe extensive corrosion of the annular plate.
While API prohibits patch work repair of the annular plate can anyone in a similiar situation share his experiences with us and tell us what their quick fix solutions were?
Many Thanks

 

[MJCronin]

nrp,

Are you aware that there are API standards on storage tank assesment and repair ?

There are many firms that will provide objective, third-party review and propose repair solutions.

Google "storage tank", consultant, repair and API

Review your results.......


MJC

 

[apiguy]

Have you gone inside the tank and inspected the critical zone area? Ultrasonics or MFE will reveal the extent of your underside corrosion. If there is no seal between the foundation and the bottom plate extension, corrosion is inevitable! Most of the time though the scale corrosion you see at the very edge does not extend very far under the tank. Proper cleaning of the area and a good seal usually does the trick.

The APIGUY....

 

[chicopee]

nrp12345- according to API 650 section 10, the bottom annular plate can be repaired w/ certain conditions. Have you explored all the possibilities offered in section 10?

 

[JohnGP]

nrp12345,

Further to MJCronin's response, API STD 653 "Tank Inspection, Repair, Alteration, and Reconstruction" provides guidance on repair of tank bottoms (and remainder of tank), including the use and limitations regarding welded-on patch plates.

Regards,
John