Assessing the erosion-corrosion processes of metal matrix composites in slurry conditions by electrochemical techniques

In the oilsands industry the materials are subjected to a combination of erosion and corrosion damage. The ore extracted from the open pit mining operation is crushed and is combined with warm water to produce slurry. During the transportation of the slurry to the upgrading facilities, the sand particles impact and abrade the materials surface producing mechanical degradation and the damage is severely increased by the corrosion effects of the carrier fluid. Metal matrix composites are used to reduce the negative effects of the erosion-corrosion in the oilsands industry; they present a good combination of hardness, impact and corrosion resistance. Understanding their erosion-corrosion behavior is vital to improve their performance. In this study the erosion-corrosion behavior of three different metal matrix composites (with WC as the reinforcing phase) is investigated by analyzing their electrochemical response under different conditions. The matrix materials are: NiCrBSi alloy, NiCrMo alloy and a FeCr alloy. The effects of the sand concentration, temperature and velocity is assessed by potentiostic tests and the critical conditions are established. The NiCrBSi and the NiCrMo alloys show low current density values when the sand concentration is below 500 mg/L and seems to be stable as the testing time is increased, however, when higher sand concentrations are used, the current density values is dramatically affected. In the other hand, the FeCr alloy shows high current density values even at low sand concentrations and the current increases linearly as the time increases suggesting and activation dominated process. The degradation regimes are described as flow enhanced corrosion, erosion-corrosion process and erosion dominated process and the results are supported by the surface analysis of the metal matrix composites.