Hi at the crude oil tank floating roof out rim top section had a pitting corrosion all aroud the floating roof the strange thing not the whole floating head wall had corrosion because the half of it coverd by the oil . This tank was filled by 20 % slope oil in 2004 . I n regard to that could any one tell why the corrosion happend at the out rim (vapor space) is it slufice pitting corrosion due the slufide is vlotile from the oil more information will be helpfull Many thanks

What I could gather from the question is that you are refering to the vapor space corrosion in the rim space, especially on the vertical face of floating roof in that location. Pl. mention following points 1) Product (2) Whether rim space and tank shell are painted. (3) What sort of seals are being used & condition of seal system. (4) In case it is a crude oil tank, %age S, Cl- etc to be mentioned. (5) Whether heating steam coils are installed in the tank Ok Product is crude oil and in 2004 operation add the slope to the tank . 2- rim space and shell not coated just one meter from the bottom (water section). 3- The fabric seal and S.S shoe. 4- %s and Cl not yet but I will conseder them were high in 2004 because the slope addition. 5- No heating steram coil installed. I was think the slufide condense at the vapor space and cause the corrosion to the top of the rim while the bottom of the rim was protected by the oil . Thanks

[updated:LAST EDITED ON Jun-12-05 AT 11:00 PM (CDT)]I agree to your diagnosis - it is a vapor space corrosion. May be at next M&I of the tank, you will paint the roof portion. The portion is a bit difficult to sandblast & may be you have to go for self-priming epoxies after manual cleaning to St-3 level. In one of my worst experience, I have seen leakage from that location, after a service of 35 years. The location was never properly painted. One question - do you have a flame arrester /Breather Valve in rim space ? If yes, any modification done to these after you started adding slop to crude ? Any discussion will be appreciated. regards