aluminum alloy corrosion of tank inner floating roof 3

[edmenper]

Dear All,
Appreciate if anyone may have experience with aluminum alloy corrosion of the support legs and sheeting of an inner floating roof tank. The aluminum alloy is 6063 and the medium stored in the tank is platformate to be used in gasoline blending.
Thanks

 

[IFRs]

The sheeting is likely not 6061, but probably one of the 3000 alloys. In any case much more information is required for a good response. How old is this floating roof? Where is the tank located? What is the brand or manufacturer of the floating roof? Is it a non- or full-contact variety? What was the storage temperature? When was it last inspected? What is the storage temperature? Was it landed on it's logs often? What condition are the pontoons, end caps, sheet support beams? Is there any debris on top of the skin? What is the pH of the liquid? Was there a water bottom? Is there a railroad or underground pipeline nearby? Is there active cathodic protection on the tank? Does the tank have mixers or spargers? Is there a floating suction? How and when was the damage found? How was the tank operated? Do you have the filling / withdrawal history? etc. I've been in this business since 1977, seen many damaged aluminum floaters and there is often a long story behind each failure which takes some hard detective work to complete.

 

[edmenper]

IFRs, Thanks for your input.
This aluminum inner floating cover was installed in 2001 by the company TAISA, for a storage tank of Platformate at ambinent temperature (`30 deg C). The tank has one mixer,and the main damage (partial floating cover collapse) was at the area of the mixer. Thinning of the sheeting (alloy 3003 H14)was observed, and some pontoons were filled with liquid. Corrosion was also observed on some of the legs (see attached picture) and the material was confrimed to be alloy 6063 T5. Tank is not equippped with an auto minimum level stop for the mixer. The cover has landed quite often on its legs, the level has been quite erratic over the last 7 years. There is no cathodic protection (no need).
Thanks for any further tips that may assist with the troubleshooting.
Regards.