Abstract Two systems have been developed for the detection of sand in surface gas lines. One systemis based on the detection of sand grain impacts on a piezoelectric crystal and the other uses anerodable resistor placed in a gas stream. Laboratory experiments and tests on the well site have proved the suitability of both techniques. Quantitative calibration of the two systems under operational conditions is in progress. Introduction In areas where Band production of oil or gas wells forms a potential problem, it is advisable to install sand detection devices. Early remedial action on a sand producing well will increase the chance of success of the treatment. To ascertain the need for such action, the sand detectors should preferably provide quantitative information on a continuous basis. Apart from conventional wellhead sampling, only one system of sand detection is known to be in use. With this method a preselected level of erosion is detected by the sudden pressure change in a thin-walled metal capsule when it is finally penetrated by the sand. At least two continuously monitoring sand detection systems have been proposed. One system uses an erodable radioactive disc; metal losses due to erosion are determined by measuring the resulting decline in the level of radioactivity of the disc. The other method has been proposed by Stein et al. for downhole detection of sand influx in a well. He states that the additional noise generated by sand impingement ontubing is proportional to the total kinetic energy per unit time of the impinging particles. The mass flow of the sand produced is derived from the actual acoustic noise level minus the level that is expected at given flow conditions. As no suitable continuously monitoring sand detection system was known to be commercially available, scouring experiments were initiated, which resulted in the development of two prototype detection systems. In the first system apiezo-electric crystal is used to produce sand impact signals. Only those impacts can be detected whose peak amplitude can be discriminated from the background noise caused by the turbulent gas stream. The amount of sand produced can be derived from the number of impacts counted, the amplitudes of their signals and the velocity of gas flow. The system has to be calibrated under actual field conditions. The second system involves direct measurement of the erosive effect of sand in a gas stream. It is based on measurement of the increase in resistance of an erodable resistor which is placed in a sand-laden gas stream. Adequate sensitivity can be achieved by selection of suitable erodable elements. Here again calibration under field conditions is necessary.