For over half a century, floating roof seal assemblies have been, at most, an afterthought. Very little consideration was given to how a seal would function, and even less given to actual emission control. Little thought was given to product compatibility, tank conditions, shell deformations and tank cycling. As long as the gap between the floating roof and tank shell was bridged with a device of some sort, the tank was deemed operational, giving a false sense of safe operation and emission control.
The typical seal system installed on steel floating roofs has remained consistent for the past 30+ years. A primary mechanical shoe seal comprised of galvanized or stainless steel plates with a urethane or Teflon fabric curtain and a secondary seal with galvanized or stainless steel compression plates and a urethane or flexible extrusion tip have been the standard. A few variations were available, with ‘off the shelf’ seals being the most commonly used in storage tanks. These often required field modification during installation, resulting in less effective emission control and premature seal failure.
With the advancement of VOC detection systems, today’s tanks are under more scrutiny than ever and, with that, the need for advanced emission controls has never been higher. Protecting the environment and reducing operational losses is a priority for all tank operators. The need for a seal system designed specifically for this application is now necessary, and what was once considered the ‘off the shelf’ standard is no longer acceptable.
Evolution Of Seals
A seal system designed for today’s applications must take into account numerous factors. Shell deformation, tank construction, annular dimensions, rim geometry, product compatibility and weather conditions are just some of the considerations needed to ensure an effective seal is achieved. A seal designed for one region may not meet the operational requirements of another. The ability to design, model and ‘test’ a seal assembly is critical to ensure operating conditions can be met prior to seal installation.
Data collection, engineering, design and testing are now necessary to ensure a long lasting, regulatory compliant and fully functional seal is provided. Today’s seals must meet not only today’s requirements but also tomorrow’s evolving standards. As industry evolves so must our processes, designs and applications for seal operation. The decisions and provider choices we make today are critical to both the survival of our industry and our planet. Careful thought must be exercised when choosing a seal design and provider.
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