Repairs of #6 fuel oil tank

[Paperpete]

I am not sure that this is the right forum for this question. If any of you feel that there is a better one please respond and let me know.
I have a problem with a 70,000 gal oil tank. The sheetmetal roof is corroded. Actually a few small holes has developed (approx. 1/8" diameter). When the top manhole was opened and I looked with a light and a mirror I could see that the structural members holding up the pitched sheet metal roof appeared to in great shape. The walls of the tank also appeared to be in good condition. The problem I am facing is how to replace or repair the roof. I have recieved a quote for approximately $18,000 just to clean it!. I dont think that welding on top of this tank is a good idea unless it is completetly cleaned out. It may be possible to put a new sheetmetal on top of the old and fasten it down in some other way but welding.Could anyone give me some guidance or recommend a reputable company that could take on a job like this in the North East (Mass).
Thanks

 

[aybee]

make sure that the beams are not corroded ,if the roof has holed then you can get corrosion bewteen the beam top and the roof. uits probably an API 650 tank min thickness3/16" so there is not a lot of CA. get the roof checked out thoroughly to make sure that it is not full of deep corrosion pits which have not yet ruptured. You would need to gas free the tank to do welding but you may need to do this to get inside and inspect the roof beams. If you dont/cant weld then you are faced with temporary patches. epoxy mastic/plate to cover the holes or possibly overspray with one of the polyplastic spray coatings which proved a very durable skin..the downside is you cant check the roof again through the coating. You could retro fit an aluminium dome roof...not cheap.
Check teh bottom strake where it meets the annularfor internal thickness using UT. may have a water bottom you didnt know you had

 

[rkchalla]

I would strongly suggest doing an API-653 inspection on the tank, prefarably internal. If welding is a problem, a bolted roof connecting to the structural members can probably work.
A "Good" Inspection company might be able to help you with the issues.