Producing sand during oil and gas production is unavoidable. Sand is produced along with oil and gas
and its deposition in pipelines is a significant risk as it can cause pipe corrosion and flow assurance
difficulties. It is therefore key that flow conditions are sustained to guarantee lack of deposition of sand
particles. The minimum combination of mixture velocities that guarantee continuous sand motion is
known as the minimum transport condition (MTC). Here, we investigate the effect both of sand
concentration and particle diameter on MTC in a horizontal pipeline in the stratified flow regime. Non-
intrusive conductivity probes were utilised for the detection of sand. These sensors are commonly used
for the measurement of film thickness in gas and liquid flows, but we demonstrate their use here for sand
detection after suitable calibration. It was observed that at the ultra-low sand concentrations of our
experiments, MTC increases with both sand particle diameter and concentration. We developed a new
correlation based on Thomas’s lower model but included a sand concentration correction term that also
applies at low particle concentrations. The correlation’s predictions compared favourably with our
measurements at MTC as well as data obtained from the open literature at medium concentrations.