Tank inspection method

A tank inspection method comprising the steps of:

• supporting a cylindrical tank, with a central axis of the tank crossed with a horizontal plane such that openings provided at both ends in a direction along the central axis of the tank become an upper opening and a lower opening;
• injecting water in which water is injected into the tank from the lower opening of the tank supported in the supporting and air inside the tank is discharged from the upper opening, and the tank is filled with water by causing water overflowing from the upper opening to flow into a water tank through an overflow line;
• increasing pressure in which water pressure inside the tank, filled with water in the injecting water, is increased to a predetermined pressure by pumping water to the lower opening, with an upper valve closed, the upper valve adapted to open and close an upper flow path connected to the upper opening of the tank;
• and
• draining water in which water is drained from the lower opening of the tank after the increasing pressure ends,
• wherein:
• the overflow line is provided with an upper valve and an overflow valve in the order from the upper opening to the water tank;
• an air supply line that branches from the overflow line and is supplied with air from an air supply unit is connected to the overflow line between the upper valve and the overflow valve;
• the air supply line is provided with an air supply valve;
• in the injecting water, the upper valve and the overflow valve are opened, and after water overflowing from the upper opening flows into the water tank through the overflow line, the upper valve is closed;
• in the increasing pressure, the water pressure inside the tank is increased to a predetermined pressure with the upper valve closed;
• and
• in the draining water, the overflow valve is closed, the upper valve and the air supply valve are opened, and air from the air supply line is pumped to the upper opening of the tank.