Do a search. Velocities are determined based on economics. For clean fluids, this is a balance between the cost of pipe (procurement, fabrication) versus the cost of pump energy. For slurries, acid etc., there are practical maximum velocities associated with materials durability which may be well below these "economic" numbers. For most piping, the only harm you do by running velocities higher than economic is to waste pump energy- the notion that the upper limits are set by erosion is, in most cases, just plain wrong.