Floating Roof Seal Types and Selection Guidance
By: Doug Bayles, P.E., Manager of HMT Engineering Services
Above ground storage tanks come in all shapes and sizes. Some tanks have fixed roofs, some are open-top with external floating roofs (EFR), and others have fixed roofs or covers with internal floating roofs (IFR). A key element in controlling emissions in an above ground storage tank is having a high quality perimeter seal on the floating roofs.
Since the beginning of hydrocarbon processing, bulk liquid storage has been through the use of above ground storage tanks. There have always been concerns regarding environmental effects and product loss from storage facilities. The first storage tanks were built with fixed supported roofs. Due to large vapour spaces and open venting, emissions and loss of stored product from above ground storage tanks became a serious issue. These large vapour spaces made fixed roof tanks very susceptible to vapour space explosions, with very serious consequences for tank owners and their neighbours.
In the early 1920’s, the concept of a floating roof was developed to address environmental and product loss concerns. The floating roof consisted of a circular, steel roof that floated directly on the surface of the stored product. The seals were designed to span the gap between the outer rim of the roof and the tank wall, thereby minimising vapour emissions from the perimeter of the roof. The seals were attached to the floating roof and not to the tank, therefore, allowing free movement up and down as the level of the product changed within the tank. The floating roof and seal combination reduced vapour emissions and the chance or vapour space explosions. An additional advantage of this system was that the rim seal, greatly reduced the amount of water allowed into the product.
