Please supply more information eg. SIZE;CONTENTS; iS THE PLATE CORRODED;WHAT IS IT MADE OF S/STEEL

pipeingg(indutrial)
THANK YOU VERY MUCH FOR THE RESPONSE.

Dear Sir,

Sorry for not giving more information at the outset

Tank Stores Gas Oil
Diameter  = 23.5 meter
Height    = 11.7 meter
Tank is Steel, I presume equivalent to ASTM A 36
The Tank is riveted construction.
It had been in service for 50+ years
Bottom shell is 12.5mm and in good shape
Bottom Plate is 9mm and is corroded in areas. We are in the process of repairing and replacing sections that are away from rivet lines
We have conducted a vacuum box test on the horizontals and they are not leaking.
But we feel that the joint Bottom to first shell may have some leaks. This we have not established so far.
However we need to provide some safety against possible leaks once the tank is loaded for hydrotest.
Also we need to maintain the integrity of the riveted connectoion when boublers are being introduced close to the rivet line. Some weld connections are around 10 to 20mm from the rivets
Hope this is adequate
Thank you
Gamma

Calling 513613, Thankyou.    You will have to conduct another vacuum box test on your horizontals when all welding is complete. Tig welding would be the way to go as you can control the size of the  heat effected zone more easily when coming to fit your Boublers rather  than stick Welding.After this length of time the steel will have become impregnated with gas oil and be carbon enriched. Welding in new pieces could be difficult,However I've always placed patch plates on these tanks and welded them  on the outside with M.I.G.  flux core process using .6dia wire  a small 3-4mm fillet weld should be ample. This would also overcome possible  leaks durring hyrotest ,remember my good friend rivets due to there use and age can not be saved all the time ,this job wil cost more but will be cheeper in the long run and will give the tank a longer life expectancy. If the tank is enclose you may wish to purge the tank with nitrogen as another safty factor.Please let me know how you get on and goodluck!                             

Have you considered having the tank relined?

pipeingg(industrial)

Dear sir,

Your advice is very helpfull.Thank You again. I will keep you posted on the developments. As adviced I will use TIG welding around the rivets and rivet loine.
Gamma