About 15% of failures in oil and gas production at gravel bags, nozzles, a.s.o. are caused by erosion corrosion. Production rates are often limited by critical flow velocities which are unknown in most cases. A new testing facility for a high velocity three phase flow consisting of a gas flow loop and a jet impingement was invented, built up and achieved. Flow velocities between nozzle and specimen have been determined by theoretical CFD simulations and by particle image velocimetry. Tests were conducted on steels (carbon steels (J55, L80, C95), stainless steel (AISI 410), duplex steel (S31803), superaustenitic steel (N08028) and Hastelloy C276 (N10276)), which are used in tubings for the gas and oil industry. Flow conditions of a gas condensate well have been investigated using a gas-oil-ratio of 3x103 and 27 g/l NaCl containing water as liquid phase. Sand content with grain size below 0,15 mm was corresponding to practice. CO2 with a partial pressure of 15 bar was used as gas phase. Mass loss rates have been determined with optical profilometry. Damaged surfaces were investigated by optical and by scanning electron microscopy. Critical flow velocities for investigated materials are presented and effects of materials, mechanical properties, testing time and sand content are critically discussed. Damaging happens by erosion enhanced corrosion (carbon steels), corrosion affected erosion (13% Cr steel) and erosion (highly alloyed steels).