Tank seals for external floating roofs, design and maintenance
For decades external floating roofs have represented the preferred way of storing hydrocarbons as crude oil, gasoline, and many related products stored before or after refining.
External floating roof tanks, an introduction: The design is based on having an open top circular tank shell, where inside a steel roof is floating in direct contact with the product stored. As the roof is floating in direct contact with the product this approach reduces volatile emissions while it allows for vast quantities to be stored, and therefore has been implemented on large scale storing hydrocarbons.
To allow the external roof to freely float there is an annular rim space between the tank shell and the floating roof. This permits smooth travel of the roof within the tank and prevents the roof from getting stuck in the tank. Tank seals are used to seal the annular space, primarily to reduce the emission and evaporative loss from the stored product and to maintain the product integrity by reducing the amount of (rain) water that can enter the tank. A good rim seal also helps to centre the roof in the tank and will prevent built up of excessive corrosion on the tank shell.
In this article we will address the available seal designs, seal material selection and tank seal inspection for seals on external floating roofs.
