A slurry impingement rig containing 6 wt.% SiO2 particles was used to investigate synergistic erosion–corrosion behavior of X-65 carbon steel at various impingement angles. Maximum erosion–corrosion and erosion rates occurred at impingement angles of about 25 deg and 40–55 deg, respectively. The synergy value highly depended on the impingement angle. The formation of patches of porous corrosion product followed by the formation of corrosion pits led to a positive synergy under impingement angle of 25 deg. At higher impingement angles, the absence of pits probably due to the formation of a more durable tribocorrosion layer resulted in a negative synergy.