HELICAL TUBE OF STEAM GENERATOR: COMPARATIVE STUDY OF CORROSION RESISTANCE OF NICKEL BASE ALLOYS AS THE PRIMARY MATERIALS

Nickel base alloy 800 and 690 are considered to be used as helical tube of steam generator. The heat exchanger is coupled with High Temperatures Gas-Cooled Nuclear Reactors (HGTR) as the source of heat. Nickel base alloys were found to have a better performance in terms of corrosion resistance compared to other types of materials for the helical tube of steam generator. This paper reviews the corrosion resistance properties of Ni-base alloys at high temperature and different pH. It is observed that corrosion resistance of Alloy 690 has a better performance on resisting the deterioration in the harsh environment of reactor. Alloy 690 samples were tested at different pH and at high temperatures by using electrochemical methods. The result showed that corrosion potential of Alloy 690 in acidic solution is higher rather than in neutral or alkaline solution is suggested due to the activation of passive film and then allow the passive film to grow thicker. At lower temperatures, 285oC, and in neutral solution, Ecorr of Alloy 690 is around -0.5 V. It is thought that this behaviour is closely related with chemical composition of passive film. The detection of potential corrosion as a function of temperature shows reduction from low to high temperature of Alloy 800 and 690.