Installation standards for lightning protection devices in petrochemical storage tanks

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Installation standards: A lightning receptor, commonly known as a lightning rod, serves primarily to capture the discharge that occurs between thunderclouds and the ground. Petrochemical storage tanks are classified as Category I lightning protection buildings in Zone 0 or Zone 1. Lightning protection measures mainly consist of lightning rods and lightning strips that intercept lightning strikes, as well as metal components. Based on existing ** and industry standards, lightning protectors for petrochemical storage tanks shall comply with the following requirements: (1) Floating roof tanks or internal floating roof tanks, as well as steel tanks used for storing flammable liquids, should not be equipped with lightning rods ； (2) A lightning rod may not be installed on pressure storage tanks (spherical storage tanks for liquefied hydrocarbons) ； (3) For steel storage tanks with a wall thickness of 4 mm or more, when a vent valve equipped with a flame arrester is installed on the tank top, the tank itself shall be used as a lightning receptor ； (4) For steel storage tanks with a wall thickness of 4 mm or more, if a vent valve without a flame arrester is installed on the tank top, a lightning rod should be installed on the same tank top ； (5) When the wall thickness of steel storage tanks is less than 4 mm, lightning rods shall be installed on the tank roof. Down conductor: A down conductor is a conductor used to conduct lightning current from the lightning receptor to the grounding device. The wall of metal petrochemical storage tanks can be used as a lightning protection down conductor, but galvanized round steel or galvanized flat steel should be used at the tank base to connect to the grounding system. Materials and minimum cross-section of down conductors: According to the Code for Design of Lightning Protection of Buildings, when galvanized round steel is used for lightning protection grounding down conductors, the diameter of the above-ground portion should be ≥8 mm; in actual construction, Ф10 round steel is commonly used for such grounding down conductors. The diameter of the underground part is ≥15 mm; in design and construction, Ф16 round steel is commonly used, as it is cost-effective and practical. When galvanized flat steel is used, the cross-sectional area should be no less than 50 mm2, and the thickness should not be less than 2.5 mm. In the design of petrochemical storage tanks, the standards set out in the \"Regulations on Safety Design, Construction, and Operation of Large Floating Roof Tanks in China’s Petrochemical Industry\" are followed; galvanized flat steel with dimensions of 40mm×4mm is used. The distribution of down conductors: **Both standards and industry regulations specify that lightning protection systems for Class 1 buildings must have no fewer than 2 grounding down conductors. The Code for Design of Lightning Protection of Buildings stipulates that for Category I buildings against lightning induction, “a down conductor should be used to ground the area around the metal roof every 18 m to 24 m.” ”The Technical Guidelines for Light Oil Storage Tanks stipulate that the spacing between downlead wires shall not exceed 18 m. Most petrochemical storage tanks are metal tanks; the spacing between the down conductors should not exceed 18 meters, and they should be distributed evenly around the tank. The impulse grounding resistance of each down conductor should not be greater than 10Ω. In areas prone to mechanical damage, the grounding wire in the section ranging from 1.7 m above the ground to 0.3 m below it should be installed concealed, or protected using galvanized angle steel, modified plastic pipes, or rubber pipes. The disconnecting clip is used to connect the grounding down conductor to the grounding device. It is installed on the down conductor at a height of 0.3 m to 1.8 m above the ground. The connection point should be galvanized or its contact surface should be tinned. It is secured using two M12 stainless steel bolts along with anti-loosening washers, and the contact resistance value must not exceed 0.03Ω. A grounding device is used to conduct lightning current and dissipate it into the ground; it consists of a grounding electrode and grounding wires. A grounding electrode is a conductor buried in the soil for current dissipation. The distance between the grounding electrode and the tank wall should be greater than 3 m, and the impulse grounding resistance should not exceed 10 Ω. When multiple grounding electrodes are arranged closely together in the soil, the area over which the lightning current can spread is reduced. This hinders the current from spreading in a hemispherical pattern throughout the ground, resulting in a shielding effect on the grounding electrodes and a decrease in the efficiency of the grounding system. Therefore, the Code for Design of Lightning Protection of Buildings stipulates that the distance between vertical grounding electrodes should not be less than 5 meters, and the same applies to the distance between horizontal grounding electrodes. A grounding wire is the connecting conductor that runs from the down conductor disconnect clip to the grounding electrode. The standards specify that galvanized flat steel of 40mm×4mm should be preferred for grounding wires. The grounding wire is laid along the circumference of the tank, and its distance from the tank wall should be greater than 3 meters.