1. Direct Lightning Strike Protection (LPS Assessment)
Metallic Tanks (Shell/Roof Thickness $\ge$ 4mm Steel / $\ge$ 7mm Aluminum): The tank shell itself acts as an inherent air-termination system capable of safely conducting and dissipating lightning currents. Dedicated lightning rods (air terminals) or overhead wires are not required, provided the tank is properly grounded and equipped with flame arresters.
Metallic Tanks (Shell/Roof Thickness < 4mm Steel or Aluminum): Independent air terminals (lightning rods, masts, or overhead shields) must be installed. The zone of protection (calculated using the rolling sphere or angle method) must completely cover the tank shell, breathers, vent valves, and all other protrusions.
Non-Metallic / Fiberglass Reinforced Plastic (FRP) Tanks: Independent air terminals or an overhead catenary wire system must be installed to ensure lightning strikes the protection system rather than the tank shell. All isolated metallic fittings on the tank must still be bonded and grounded.
2. Earthing and Grounding (The Most Critical Element)
Grounding Point Quantity: Steel storage tanks must have at least two grounding points arranged symmetrically along the perimeter of the tank base.
Spacing Requirements: The circumferential spacing between grounding points must not exceed 30 meters (larger diameter tanks require additional points).
Ground Resistance: The impulse grounding resistance must be $\le$ 10 $\Omega$. A unified grounding system is highly recommended, integrating lightning protection, static dissipation, and electrical equipment safety grounding.
Down Conductors: The steel tank shell can serve as a natural down conductor. If dedicated down conductors are used, hot-dip galvanized round or flat steel must be routed down the side, with a testing disconnect link installed between 0.3m and 1.0m above grade for routine inspections.
Foundation Grounding: Connect the concrete foundation rebar (natural grounding electrode) to the artificial grounding grid to maximize system reliability.
3. Equipotential Bonding of Accessories & Flame Arresters
Metallic Component Bonding: All metallic attachments-including pressure-vacuum vents (breather valves), flame arresters, gauging hatches, manways, thief hatches, and drain lines-must be equipotentially bonded to the tank body. (Flanged or bolted connections with $\ge$ 5 bolts and zero corrosion do not require external bonding jumpers; otherwise, flexible braided copper straps must be used).
Flame Arresters: Every vent line or pressure-vacuum valve discharging into the atmosphere must be fitted with an approved flame arrester to prevent lightning strikes from igniting localized fuel vapors.
Floating Roof Tanks (If Applicable): Shunts or flexible tinned copper cables (minimum cross-sectional area of 50 mm²) must bond the floating roof to the tank shell at multiple locations (maximum spacing of 30 m) to eliminate potential differences between the roof and the shell.
4. Piping, Bunding, and Static Bonding
Inlet/Outlet Process Piping: All metallic process piping connected to the tank must be grounded at the point of entry. Parallel pipes spaced less than 100mm apart must be cross-bonded every 30m. Pipe flanges with fewer than 5 bolts must be fitted with continuity bonding jumpers.
Secondary Containment / Bunds: Steel dikes, bund walls, or spill containment pallets must be integrated into the grounding grid. If the tank sits on an insulated anti-corrosion barrier that prevents natural self-earthing, dedicated grounding rods must be driven.
Static Dissipation (Loading/Unloading): During fuel transfer operations, tanker trucks must be bonded to the grounding grid via dedicated heavy-duty static grounding clamps (tied to the main grounding system) to prevent static discharge sparks during filling.
5. Instrumentation & Electrical Surge Protection (LEMP Mitigation)
The metallic enclosures of all field instruments mounted on the tank (such as temperature, level, or pressure transmitters) must be electrically bonded to the tank shell.
Signal and power cables must be routed through hot-dip galvanized steel conduits or utilize shielded cables, with the conduits/shields grounded at both ends.
Surge Protective Devices (SPDs) with voltage protection levels matching the equipment's withstand voltage must be installed at the entry point of control rooms or power distribution enclosures to protect automated systems from Lightning Electromagnetic Impulse (LEMP) damage.
