primary seal should be considered for all floating roof tanks, and listed below are a variety of choices. Mechanical shoe seals and resilient filled seals (i.e. liquid-filled tube seals and foam log seals) are the two main primary seal types. Tube and foam log seals risk "puncture", which would render them useless and represent environmental waste in disposal. They do, however, provide a "soft" connection against the tank which may be beneficial if the inside surface of the tank shell has a finished paint system. A mechanical shoe seal, which generally has a longer life span than either the tube seal or the foam log seal, represents the Best Available Control Technology available today.Two optional mechanical shoe seals are available; both offering "in-service" installation. The Channel Hanger seal is the more economic system, and is generally utilized in new tank construction and for retrofits where the annulus is in the "normal" range. Where significant out-of-roundness or unusual rim space measurements are found, a Compression Shoe seal is available. The Compression Shoe seal, which can provide a significant force along 90% of the circumference of the tank shell, helps minimize the potential for gaps between the shoe and the tank shell.


Secondary Seals are normally required for external floating roof tanks, and may or may not be required when an external roof covers the floating roof. However, some localities require a secondary seal on a covered floating roof if the primary seal is a vapor mounted seal. Mechanical shoe seals, by their nature, are liquid mounted, and both tube and foam log seals can be liquid mounted. A compression plate secondary seal has a longer life than a "flapper". While the "flapper" offers a lower profile, it may not stand up against the environment of the stored product vapors, and therefore not be an appropriate choice. The Duo-Tip offers a lower profile than the 5" flat wiper when compression plate secondary seals are chosen.


A variety of double seal combinations exist as a mix-n-match of all available primary and secondary seals shown, as well as Double Wiper Tip seals, which offer a unique selection.


The appropriate selection of seals for use with storage tanks that have riveted shells involves many special considerations that may limit the choices. While "soft" seals, such as a foam log seal, can be utilized on riveted tanks, the soft surface does not stand up against the wear of the irregular surface of the tank shell resulting in a failed seal. Mechanical shoe seals can be adapted for use on riveted tanks, and the Triple Tip secondary seal was specifically designed for multiple contact points, which helps the seal maintain contact as it negotiates the rivet heads and butt straps of riveted tank shells.
SEAL COMBINATIONS FOR ALUMINUM FLOATING ROOFSSEAL COMBINATIONS FOR ALUMINUM FLOATING ROOFS Lightweight aluminum floating roofs require special considerations, eliminating many choices. While the foam log seal has traditionally been the seal of choice, mechanical shoe seals and flapper style secondary seals have come into preeminence in recent years. Utilization of mechanical shoe seals on aluminum floating roofs requires additional flotation where foam log seals were originally utilized.


The American Petroleum Institute (API) does not define which seal system should be utilized on any particular set of circumstances, but allows the end user to utilize the most appropriate set of seal(s). Refer to Standard API 650.The API has, however, done generic testing for emissions based on the following combinations of seals: Mechanical Shoe Seal, Resilient Filled Seal (both vapor mounted and liquid mounted), along with combinations of these seals with rim mounted secondary seals. The testing concluded that utilization of a liquid mounted primary seal (e.g. metallic shoe seal, or liquid mounted resilient filled seal) in combination with a rim mounted secondary seal provided a significant reduction in emissions when compared to primary seals alone. Refer to API Manual of Petroleum Measurement Standards Chapter 19.1 and 19.2 (formerly API standard API 2517 and API 2519).



  • 5inwiper
  • channel
  • compshoe
  • duotip
  • foamdam
  • foamlog