Abstract: It is common during the development of oil and gas fields that pipelines suffer sand wear. Continuous impacts can cause dents or scratches on pipe materials, and lead to wall thinning and even other serious problems, e.g. pipe leakage. The flow field inside the pipeline is variable and the sand is not distributed uniformly, so sand erosion mechanism is complex. In this paper, the erosion performance of 316L stainless steel at inner liner of bimetallic composite tube was studied by using the large liquid-solid two-phase flow erosion test loop, and the test results were compared with the numerical calculation results. Then, the erosion mechanism of the elbow of composite tube was proposed. It is shown that the sand wear and erosion on elbows is mainly divided into three forms, i.e., micro-cutting wear, plowing and impact deformation. The effect of secondary flow on sand movement at the elbow is significant. Due to secondary flow, the sand at the elbow moves from the extrados to the intrados and consequently the intrados zone is eroded. Under the effect of gravity and flow field, the most serious erosion occurs at the bottom of elbow outlet.