In this study the electrostatic charging behaviour of single particles of different sizes and materials were investigated during pneumatic conveying. The particles used included 3.18 and 0.79 mm PTFE as well as 3.18 mm Nylon particles. Particles were pneumatically conveyed in stainless steel (316 Grade) tubes with 4.57 mm inner diameter. Effects of conveying tube length, conveying gas velocity and pathway of particles (i.e. addition of 90 degrees elbows and smooth bends) on particles charge-to-mass ratio were studied. Results showed that the smaller PTFE particles reached the saturation charge in the longest straight tube at all conveying gas velocities tested. Whereas the other two larger particles reached saturation charge only in the longest straight tube and at the lowest gas velocity. For large particles moving in straight tubes, in general, the lowest gas velocity resulted in a higher charge-to mass ratio. The particles pathway had a large impact on their charging behaviour at high gas velocities, whereas at the lowest gas velocity, the total tube length was more influential on particles charging. Finally, the charge of the particles determined by measuring the current from the conveying line was found to be in good agreement with that measured directly by a Faraday cage. (C) 2019 Elsevier B.V. All rights reserved.