Korrosion des Hastelloy C 4 und anderer metallischer Werkstoffe in heißen,konzentrierten Salzlaugen

Corrosion of Hastelloy C4 and different metallic materials in hot concentrated salt brines In a quaternary salt brine saturated at 55°C with magnesium chloride, potassium chloride and sodium chloride, polarization curves were measured in the temperature range from 100°C to 200°C at different materials in order to study their corrosion behaviour. Steels and nickel corrode in the active state. The corrosion current density of an unalloyed steel at 100°C was about 20 μA/cm² corresponding to a removal rate of 0.2 mm/a. Iron-silicon and nickel corrode significantly slower at a rate of a few μA/cm². Steady state corrosion rates of Hastelloy C 4 and of titanium at 100°C are 10 nA/cm² and less than 4.5 nA/cm², respectively. For both materials, the susceptibility to pitting grows with the temperature and with the chloride concentration. The steady state corrosion rates of passive Hastelloy C 4 depend on temperature according to an activation enthalpy of 85 kJ/mol and become about 5 μA/cm² at 200°C. Even at high temperatures steady states are attained rather slowly within about one day. The critical pitting potentials approach the corrosion potentials in deaerated solution at a rate of about 0.8 mV/K. At 200°C the critical pitting potential is only 90 mV positive to the corrosion potential. Thus, Hastelloy C 4 may be used at high temperatures, only if it is cathodically protected.