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Hazard analysis of main problems existing in lightning protection of out floating roof tanks

Hazard analysis of main problems existing in lightning protection of out floating roof tanks

Issue Time:2021-03-19
Analysis of the hazards of the main problems

(1) Analysis of the hazard of the combustible gas concentration exceeding the standard in the secondary sealed cavity

The oil tank with combustible gas concentration in the secondary sealed cavity reaches the explosion limit range. Once the tank is struck by lightning, it will cause the secondary sealed space of the oil tank floating plate to flash and ignite. If the initial fire is not controlled, the fire will be enlarged.

An oil tank with a combustible gas concentration of more than 25% lel in the secondary sealed cavity indicates that the primary seal is not good. If the gas continues to accumulate, it can reach the explosion limit range. If it is struck by lightning, it may catch fire.

 

(2) "Wrapped" conductive sheet analysis

One side of the coated conductive sheet is in the secondary sealing rubber plate. When there is lightning current, if there is a small gap here, discharge will occur. If the combustible gas concentration in the internal cavity of the secondary seal reaches the explosive limit concentration, a flash explosion and fire accident will occur.


(3) The number of conductive sheets on the upper part of the secondary seal is not enough

The conductive sheet is actually a shunting measure of the lightning current. If the number is not enough, the larger the lightning current passes through each conductive sheet, and the phenomenon of ignition has already occurred.


(4) The resistance value between the conductive sheet and the tank wall

The resistance value between the static conductive sheet and the tank wall is far beyond the high standard requirement of no more than 0.032, the maximum value is 0, and the failure rate is 100%. The greater the contact resistance between the conductive sheet and the tank wall, the greater the potential difference formed, the greater the discharge current, and the greater the harm.