[en] Water and steam serve in the water-steam cycle as the energy transport and work media. These fluids should have no influence, through corrosion processes on the construction materials and their consequences, on the normal service of the plant. All these objectives are especially valid for the steam generators (SG). The SGs, act as a barrier between the radioactive primary side and the non-radioactive secondary side of pressurized water reactors. Their condition is therefore a key factor for plant performance, high plant availability, plant safety, and regarding life time extension. (author)