Polarization　curves　and　mass　losses　of　SAF3207　hyper-duplex　stainless　steel　under　various　conditions　were　measured.　The　damaged　surfaces　after　erosion-corrosion　tests　were　characterized　by　scanning　electron　microscopy.　The　results　showed　that　an　increase　in　flow　velocity　could　enhance　the　electrochemical　corrosion　and　consequently　decrease　the　passivation　properties　of　the　steel.　The　erosion-corrosion　damage　of　the　samples　increased　substantially　when　the　flow　velocity　exceeded　the　critical　value　of　4　m.s(-1).　The　mass　loss　rate　increased　as　the　sand　content　increased,　reaching　a　maximum　at　7wt%　sand　content,　corresponding　to　the　most　severe　electrochemical　corrosion　damage.　When　the　sand　content　was　increased　further,　however,　the　mass　loss　rate　decreased　and　then　tended　stable.　The　mass　loss　was　divided　into　incubation,　sustained,　and　stationary　periods,　with　a　maximum　mass　loss　rate　of　12.97　g.h(-1).m(-2)　after　an　erosion　period　of　2.5　h.　The　erosion-corrosion　mechanism　was　investigated　in　detail.