Alloy 625 is used in the chemical and petrochemical industry as a high corrosion resistant alloy. Due to the high costs of this alloy, it is often used as a cladding material. Within a cladding material, alloy 625 carries the corrosion properties and the base material the mechanical properties. The influence of heat treatments on corrosion properties and microstructure of different material conditions has been investigated. Within these investigations, stable annealed material shows much better corrosion properties than solution annealed and as rolled material. Different corrosion testing methods have been applied and correlated. Immersion tests according to ASTM G28 A shows pretty good correlation to a modified DL-EPR test. Critical phases have been evaluated with high resolution techniques (EF-TEM and KPFM). These investigations showed that Molybdenum rich precipitates along grain boundaries are critical to corrosion properties.