Effect of Sulfide Pollution on the Corrosion Behaviour of some Ni-Based Alloys in 3.5% NaCl Solution

In this work we are interested to investigate the infuence of the presence of Cr, Mo and Fe alloying additions with Ni and
to investigates the corrosion resistance of these alloys in chloride and chloride-sulfde containing solutions. The corrosion
behavior and the stability of Ni-20Cr, Ni-20Cr-9Mo and Ni-20Cr-9Mo-8Fe alloys in 3.5% NaCl and 3.5% NaCl + S−
solutions was investigated. Polarization measurements and electrochemical impedance spectroscopy (EIS) were used. Surface
examination and morphological studies were employed. Cr, Mo and Fe contents play a signifcant role against pitting corrosion in chloride and chloride-sulfde environments. Very small current densities were obtained for all investigated alloys in
3.5% NaCl solution compared with that obtained in chloride-sulfde environments. The alloy surface was covered by a barrier
layer protecting it from corrosion especially in case of Mo-containing alloy. EIS showed that the resistance of the passive
layer created on the diferent Ni-alloys increases with the increase of the immersion time. EIS measurements revelled that
the role of alloyed molybdenum becomes greater in the presence of sulfde. The role of alloyed Cr, Mo and Fe on the corrosion process and the barrier layer creation was discussed. The outcomes lead to the commendation of the Ni-20Cr-9Mo-8Fe
alloy for uses in sulfde polluted environments.