Lightning Protection Products

Prior to export, processed crude oil is stored in Floating Roof Tanks (FRT) to further allow any trapped gas within the crude oil to escape, and further stabilise the oil. In the oil and gas industry, FRT’s are vital in the processing of crude oil to the acceptable export specification. However, because of global climate change, the frequency of accidents which include equipment damage and fire damage caused by lightning in fuel depots is rapidly increasing with floating roof tank fire being a major threat to crude oil production.

Thus Fuel Tank Lightning protection is now an indispensable part of the oil depot safety system.

Interaction of Lightning with a floating roof tank

By design to ensure ease of movement of the floating roof within the tank shell, there exist a gap between the tank shell and the edge of the floating roof. This eliminates friction, guarantees ease of movement but creates issues in the following areas when lightning strikes.

• Sparking

When lightning strikes a floating roof, the lightning current will flow over the roof towards the edge of the roof, and at the edge there exist a discontinuity because of the tank shell-roof gap, this prevents the current from flowing through the tank shell to the ground.

• Roof surface charging

Prior to an eventual lightning strike electric charges will accumulate in the sky. This creates a difference in potential between the roof and the shell which can result in transient currents.

• Heating

The flow of high energy lightning current can cause erosion and melting of thin metal sheets and this can generate incendiary particles even around the shell-roof gap; though tanks with a thickness greater than 5mm cannot be melted by lightning.

The discussion above shows that the gap between the roof and the tank shell is a major cause of lightning voltage spark. In order to mitigate this, LEC on fuel tank lightning protection recommends RGA.

Retractable Grounding Array (RGA) is basically a self-retracting conductor. The RGA retracts and extends based on the roof level thereby maintaining the shortest electrical connection possible and by so prevents the issue associated with the use of long cables. It is made of multiple weaved strands of low resistance tinned copper wire and is typically installed on the tank shell and connected to the edge of the roof.

Society increasingly depends on petroleum products, so storage management of crude oil and its products has become particularly important. The approach to solving the lightning induced fire issue is centred on eliminating voltage differential by installing a fuel tank lightning protection system such as LEC”s Retractable Grounding Assembly.

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