In refrigeration, and in particular in the area of supermarket refrigeration systems, more and more ecology-oriented plant concepts are being implemented. The modern, environmently friendly refrigerant CO2 that is used here leads to high operating pressures. For these applications the K65 tube system is available. Tubes and fittings are made of the high-strength copper alloy K65 which has already been used for years in several industries including refrigeration. K65 allows economical installation of refrigeration systems with operating pressures up to 120 bar.