Mark Mor check with your design if the ring gap allowed will be > 1 mm. There should be built- in -cups or other protective system - if the design is external floating roof and with safe venting of leaks within limits due to air gaps between the seal ring and roof plates *peripherally). please check this. Your corrosion problem is in addition to condensation, problem could be vapor related corrosion as the floating moves up and down for load variations. Naphtha vapors (sulphidic vapors) attack the roof plates, pontoon plates and support beams also, Isyour deisgn - pontoon type or box type fixed for floating roof? Before increasing gap between the seal ring and floating roof - because of this specific problem - ensure that you do not get into excess venting of naphtha vapors beyond design limits. There have been case histories of floating roof collapse in naphtha tanks due to such inadvertent increase and fire and explosion incidents reported elsewhere. The Oakhlahome incident in 2003 - fire and explosion in naphtha tank - will give you details. I do not remember off-hand the reason for the failure of roof. Trust you will take care by going through design and also case histories of other user plants before attempting any modification or short cut methods to solve a particualr problem C.V.Srinivasan Nishi Engineers Pvt Ltd India August 22,2005 E-mail:nishi@vsnl.com >Thanks for your support and really our refinery forum gains >a corrosion specialist like you. You know I am thinking >about the metallic cups that will be installed at the top of >the sleeve to prevent the humid air ingress to the sleeve >during the floating roof float up or down.