Assessing metal matrix composites for corrosion and erosion-corrosion applications in the oil sands industry

Erosion-corrosion that arises when materials are transporting aqueous slurries can be a significant problem in the oil sands industry. Interactions between erosion and corrosion are complex and. as such, it is difficult to determine the rate of material loss with sufficient accuracy for the reliable prediction of equipment lifetime. A combination of electrochemical and gravimetric techniques were used in this study to assess erosion-corrosion rates under liquid-solid impingement in a simulated recycle cooling water environment containing 5 wt% solids at 25 degrees C and 65 degrees C. One material that has been successfully used on critical production equipment is tungsten carbide (WC) metal matrix composite (MMC) applied to the surface as a weld overlay. Four WC-based hardfacing overlays with different particle size distributions were investigated in this study. These overlays comprised 65 wt% WC hard phase with a metal matrix binder consisting of mainly Ni, Cr, Si, B, and Fe. The MMC overlays were applied using the plasma-transferred arc (PTA) welding process. In static corrosion tests, little change in the corrosion rate with different WC grain sizes is observed. The smallest WC grain size distribution shows a slight decrease in corrosion resistance. In erosion-corrosion tests. the larger grain size WC-based MMC shows a slight reduction in erosion-corrosion resistance. The interactions between erosion and corrosion can be identified and are important in the MMC degradation. The corrosion mechanisms in static conditions and the erosion-corrosion mechanisms can be directly linked to the complex microstructure of the MMC.