Summary Unbonded flexible pipelines are commonly used in offshore field developments to transport oil and gas to production facilities. Sand is an inevitable byproduct from oil-and-gas production. Sand erosion has become an important concern for both design of new field developments and prolongation of existing oil-and-gas fields, especially for fields with low mixture density and high velocities. Erosion in smooth pipes can be determined with industry-standard erosion-prediction methodologies. However, these models are usually valid for smooth pipes only, with limited information available on erosion in flexible pipes. This paper presents experimental results from a large-scale erosion test of an unbonded flexible pipe. A 9.75-in. inner-diameter (ID) flexible pipe with a bending radius of 2.5 m was exposed to sand and proppant particles at velocities ranging from 30 to 47 m/s. Erosion was determined by performing weight-loss measurements at selected cut-out windows, at 0, 20, 40, 60, and 80° along the outer periphery of the carcass. In addition, microscopy analysis was performed on selected eroded carcass pieces to determine the localized erosion contour of the flexible carcass geometry. Results show that the highest erosion is found at the leading edge of the carcass strip. Experimental results are compared with computational-fluid-dynamics (CFD) simulations and industry-standard erosion-prediction methodologies.