In oil and gas fields, water pipelines often suffer from erosion-corrosion problems caused by liquid-solid two-phase flow, leading to frequent pipeline leakages and affecting normal production. Hence, the erosion-corrosion characteristics of 90° horizontal elbows of carbon steel in liquid-solid two-phase flow conditions (namely sand and 3.5%NaCl solution) was assessed via a home-made pipeline two phase flow experimental setup to simulate the actual service conditions of oil and gas field water pipelines. The aim is to reveal the erosion-corrosion damage mechanism of carbon steel elbows in these conditions and to provide guidance for corrosion protection. Meanwhile, the weight loss method was used to quantify the erosion-corrosion rates, and surface analysis techniques were used to characterize the erosion-corrosion morphologies. The results show that in corrosion conditions of merely 3.5%NaCl solution without sand, the elbow has good corrosion resistance; in erosion conditions of merely 3.5%NaCl solution without sand, it has good wear resistance. However, in liquid-solid two-phase flow conditions, the elbow suffers severe erosion-corrosion damage, particularly on the outward facing side, bottom and outlet of the elbow. The erosion-corrosion, where at the outer edge at the bottom area of the pipe with an axial angle of 30°-60° is relatively less. In general, the erosion-corrosion rate should include items such as pure corrosion, pure erosion, and the interaction between corrosion and erosion. In the present case, the item of erosion-corrosion interaction rate is rather higher, and the other two items is relatively lower. In fact, the erosion-corrosion interaction rates reached 41~56 times the pure corrosion rates and 45-112 times the pure erosion rates. In the interaction rates, the change in corrosion rate caused by erosion accounts for as much as 70% to 80%, which is significantly higher than the change in erosion rate caused by corrosion, and both are positive values. Therefore, the interaction between erosion and corrosion is the main cause for the sharp increase in erosion-corrosion of the elbow, as the two factors promote each other. In summary, erosion in the liquid-solid medium is the main factor leading to the failure of the carbon steel elbow. The results provide a scientific basis for pipeline protection in erosion-corrosion environments.