Asthedemandforfossil fuelsin variousindustrial fieldsis rapidly increasing, economic utilization of non-traditional oil with relatively rich reservesis being considered. Under these situations, the pipeline steel structuresused for transporting resources suffer severelyfrom thecombined action oferosionand corrosion owing to the erodentssuch as bitumen, sand, etc.,containedin non-traditional oil.It is generally considered thatthe corrosion reaction can be facilitatedin erosion-corrosion environmentscompared with the static corrosion environmentsdue mainlyto the unstable formation or detachment of corrosion products on the steel surface by the collision of the erodent particles.Thus, further anodic dissolution of the steel (M→Mn++ ne-)at the solution/matrix interfacecannot be effectively suppressed,leading to severe surface degradation and remarkable shortening of the lifespanof steel.Accordingly, the high Mn steels withsuperior mechanical properties and wear resistanceareproposedfor the promising candidates of the slurry pipeline steels in the petrochemical industry field. However, the preciseerosion-corrosionmechanism of the high Mn steelshasnot beenclearlyelucidated,and evensome conflicting resultshave been reportedpreviously.For these reasons, the erosion-corrosion behaviorsof the two different types of high Mn steel, API X70 and 9% Ni steelin flow accelerated corrosion (FAC) and slurry erosion-corrosion (SEC) environments wereinvestigatedin this study. The erosion-corrosionresistancewereevaluated primarilyby the electrochemical tests andweight loss measurements.The changes of surface and cross-sectional morphologies after the FAC and SEC tests, were also observed by field-emission scanning electron microscope. Based onthe erosion-corrosion experimental results, erosion-corrosion parameters were obtained and distinguished into four components to quantify the synergistic effects (i.e. erosion-enhanced corrosion, corrosion-enhanced erosion).The highest erosion-corrosion rates and severe wear scar morphologies on the surface of API X70 steel suggest that the steel is the most vulnerable to erosion-corrosion in a neutral aqueous solution with SiO2particles. Cr-free high Mn steelshowed comparatively higher erosion-corrosion resistance than API X70 steel because of its superb wear resistance caused by the high hardness. On the other hand, 9% Ni steel and Cr-added high Mn steel showed the lowest erosion-corrosion rates, which may be resulted from the Ni and Cr enriched oxide layer, respectively. Ni-enriched oxide and Cr doped Fe based oxide can act as the physical barrier against penetration of corrosive species and collision of the erodent particles.Therefore, the addition of Cr in high Mn steels can be an effective metallurgical strategies for enhancing the erosion-corrosion resistancein neutral aqueous environments,and the Cr-added high Mn steel can be applied to the materials for slurry pipeline used in petrochemical industry.