Before scrapping the natural gas storage tanks, they must be emptied and decontaminated; the only way to do this is burning what’s inside.
- Setting up and connection of a pipe at the top of the tank and a torch with a safety check valve; the other side of the tank will be connected to a mobile tank full of nitrogen by means of a pipe. The tank will be then pressurized by introducing nitrogen and the torch will be lit up. Thus, the nitrogen will push the natural gas inside the tank towards the torch; the check valve keeps the flame from going back inside the tank, causing an explosion. When the torch is not reached anymore by natural gas but nitrogen, it extinguishes immediately, indicating that the tank is completely empty. This is a very delicate operation, during which there will be a constant electronic monitoring of any natural gas leaks from the crucial points, i.e. the joints of the pipes and near the torch.
- Then, the torch and all pipes are disconnected; the manholes are opened and the tanks is forced ventilated with a flameproof fan. Monitoring of the L.E.L. value with exposure meter calibrated for natural gas (this value must be lower than 4%); using a high pressure hydrodynamic unit (water jet and grinding sand), a circumferential cut will be performed around the two ends of the tank.
- Once the shearing is completed, the final decontamination will take place by means of sandblasting inside the tank, in order to remove any deposits or rust that may have grown inside the tank.
- Now the tank can be considered decontaminated and ready for scrapping.