Experimental data by the authors are further analysed to gain a more detailed understanding of the mechanisms of the plug flow and near-wall behaviour in the pipe flow of pulp suspensions at concentrations up to 4.7% by weight. The results indicate two-phase flow effects near the wall, one being that the apparent viscosity is higher than that of water. Another is that the wall shear stress estimated with the pressure drop data and a force balance is much higher than the one obtained with the measured velocity profile, indicating the presence of mechanical friction forces.