Diagram: The Retractable Grounding Reel (RGR for short) is typically mounted on the highest point of the tank with the cable extended to the roof and bolted into position. Once installed, the cable extends and retracts with the roof height.
ALPTEC’s RGR is a highly-effective and virtually maintenance-free grounding system specifically designed for floating roof storage tanks. RGR substantially reduces the risk of tank fires by subduing sustained arcs during lightning events and other electrical phenomena. The RGR is able to do this better than other methods, because designers analyzed and found ways to overcome the weaknesses of other, traditional devices for grounding floating roof tanks.
What is the Risk of Rim Fires?
A recent study has shown that at least 31% of all floating roof tank fires are caused by lightning. Floating roof tanks are uniquely vulnerable when lightning strikes nearby. The shell typically discharges its electrical charge more rapidly than the floating roof. This difference in electrical potential, increases the risk of sustained arcing, which can cause a shower of sparks at the roofshell interface.
To combat the risk of rim fires, the industry has been using metal strips called “shunts” that electrically bond the shell and roof of the tank in multiple locations. Unfortunately, the bond that these shunts establish is unreliable and creates a greater risk of sustained arcs:
Rust, waxy product deposits, and paint can line the inner wall of the shell.The floating roof can drift slightly off-center and disconnect some of the shunts from the shell in an attempt to overcome these shortcomings, facilities have used many other grounding methods. But all of these methods suffer from similar drawbacks and typically have unreasonably high impedance, especially during lightning events.Substantially reducing the risk of sustained arcs requires a reliable, full-time, low impedance, and low resistance connection between the tank shell and roof. Additionally, the connection must operate regardless of the tank wall’s condition.
The Retractable Grounding Reel (RGR for short) is the only solution that is effective in meeting the risk-reduction requirements:
The retractable, braided grounding cable maximizes surface area and adjusts its length with the eight of the floating roof, guaranteeing the lowest possible impedance/resistance.The RGR is not affected by the condition of the tank because the RGR and cable are bolted and eagled to optimal locations on the tank shell and floating roof.When properly applied, multiple RGRs on each tank provide low-impedance pathways to safely discharge lightning currents.
To resist corrosion, the reel is constructed from stainless steel and the copper cable is tinned. The RGR is designed to retrofit easily onto any existing tank, even those that are in service. It is also is easy to inspect and is designed to be very low maintenance.
To guarantee the best level of risk-reduction, the variables that can affect system impedance must be evaluated on a case-by-case basis.