Fiberglass Tank Static Protection
Lightning protection system
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Fiberglass tank fire at production and saltwater facilities are often caused by a static current discharge.
The flow of volatile fluids in and out of an insulated tank generates static charge that accumulates on the fluid surface and on the walls of the insulated tank. If the flow rate of the fluids is not controlled, often the rate of static generation exceeds the rate of its relaxation. This results in accumulation of static charge on the surface of the fluid. As the surface charge density increases, the risk of it arcing over to grounded metal structures such as the tank stick or bull plug also increases. This static discharge can ignite the flammable vapors within the tank.
Fiberglass tanks at production and disposal sites are generally installed as part of a tank battery in combination with steel tanks. The risk of a lightning strike to an individual tank with a tank battery is almost impossible to evaluate, and a protection system is generally designed to protect the whole tank battery from a direct lightning strike. The protection system, however, must be designed in a manner that isolated metal bodies on the tank battery and on each individual fiberglass tank are bonded to the lightning protection system. A lightning rod based lightning protection system is installed directly over the tank vent piping infrastructure and bonding of isolated metal bodies is a core design component.
The static charge can be neutralized as it generates and safely dissipated to ground. Adequately grounded inductive neutralizers installed within the tank can increase the rate of static relaxation. The fluids and vapors within the tanks can be highly corrosive. It is recommended that the inductive neutralizers selected be made of non-corrosive but conductive materials. The inductive neutralizer must be vertically oriented from top to bottom of the tank with minimal slack. The neutralizer should be a semi-conductor with little or no capacitance.
IEEE recommends use of inductive neutralizers (such as Static Lasso). They are attached to the tank through a bolt on the thief hatch. A bonding lug is installed above the flange of the thief hatch to bond the thief hatch and static inductive neutralizer to the facility grounding system.
It is a common myth that fiberglass tanks are more susceptible to fires caused by static discharge as compared to steel tanks. Steel tanks are generally lined to minimize corrosion. This allows for in-tank static to accumulate inside the tank just like in the fiberglass tanks. Adequate measures must be taken for both tanks to dissipate the static safely to ground as it generates.
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