Factors of influence: particle hardness, density, size, shape and concentration; slurry dynamics; slurry acidity; pipe diameter, alignment and hardness. This report investigates the effects mainly of particle size, and also flow velocity, diameter, joint alignment and protective coating. Wear rates increase logarithmically with particle size increase and varied within the pipe according to proximity to the jount and circimferential position. Epoxy coating was ineffective for particles larger than 1mm. The mode of particle conveyance expressed in terms of flow regime and dependent primarily on flow velocity, pipe diameter and particle settling velocity was shown to be a major factor in determining wear characteristics. Operating with a stationery or sliding bed, an increased pipe diameter and a reduced average velocity, the area of maximum wear was displaced from the invert to the juncture of the invert and overt hemispheres. Wear rates at the juncture were found to be significantly less than the invert wear rates established by heterogeneous conveyance of the same solid material.