Z-503 tank was built and put into operation after technical commissioning in 2005 and was operated until 2011. During 6 years of operation, the inner shell of the tank has settled 26 ÷ 28 cm, while the outer shell (cover) about 3 cm. Such significant difference in subsidence of the shells caused significant damage to the structure of the bottom of the tank and pipelines in the space between the shells. The effect of these damages was the leakage of liquid stored in the space between the shells and stopping of tank operation.

Since 2011 the tank wasn’t used, but for several years it was the subject of numerous expert opinions and studies aimed at determining the causes of the failure and indicating the method of repairing the tank to restore it for further use.

The tasks during the modernization included among others the following activities:

• foundation of the tank cover on the concrete ring in the immediate vicinity of the head of the tank’s foundation. The tank cover for the time of casting of the concrete ring was lifted using a hydraulic lifting system, and after the reinforcement and the layer of the asphalt concrete, it was lowered and placed on it.
• the foam glass insulation was completely removed from the tank cover and replaced by B10 concrete lining, which will protect the tank cover against settling,
• the innovative moisture drainage system was used from under the bottom of the tank outside the cover ring.
• the new bottom of the space between shells was made with the use of the innovative compensation system, also aligning the levels between the cover and the shell of the tank.

The tank, the demolition of which had been considered, was modernized and has been in operation to this day.