The American Petroleum Institute have guidelines (see API RP14E) for the flow velocity below which erosion damage is minimized. This maximum flow velocity is a function of velocity and density, and given by this equation.
If ρ is in lb ft−3 and V is in ft s−1, then C has units of lb0.5 ft−0.5 s−1. API RP14E recommends that C=100 lb0.5 ft−0.5 s−1 for continuous service of liquid with solids, or C=125 lb0.5 ft−0.5 s−1 for intermittent service (or values of up to 200 lb0.5 ft−0.5 s−1 if the pipelines are corrosion resistant).
However, recent studies have recommended that higher C values are used, with values of 887 for 13Cr piping for "clean gas service" (see the paper "Improved Procedures for Estimating the Erosional Rates in High Offtake Gas Wells: Applications of University of Tulsa Flow Loop Derived Correlation" for more detail).