Influence of local wall shear stresses measured at different circumferential positions of a series of various piping elements (such as gradual or sudden contractions or expansions) on the removal of Bacillus spores during a Cleaning In Place (CIP) procedure was studied. The variation in residual contamination levels observed for the three tangential positions analysed was induced by the flow disturbance caused by various interacting geometric elements, essentially the bend localised upstream of the tested pipes. The recirculation zone which occurs downstream of the curved edge could explain the asymmetric behaviour of the flow expressed by the variation in wall shear stress values and velocity profile evolution for the positions investigated. The level of residual contamination observed at the lower part of tested pieces of equipment, as in the straight pipes and sudden or gradual contractions, was explained by this effect. It was also shown that certain equipment, such as sudden or gradual contractions or expansions, can induce a flow disturbance and thus affect spore removal from the surface of elements. Velocity profiles obtained by an ultrasonic Doppler velocimetry allowed the How behaviour after these hydraulic accidents to be explained. (c) 2007 Elsevier Ltd. All fights reserved.