In the oil and gas industry, erosion of pipelines and fittings caused by sand particles is one of the most common and expensive problems. Acoustic sand monitors are commonly used to provide a warning/alert when sand is being produced in pipelines. In the past, at Tulsa University Sand Management Projects (TUSMP), different operating conditions have been investigated using acoustic sand monitors to determine their effectiveness in multiphase flow. In this work, new acoustic data is gathered from sand monitors. The data is used to determine the threshold sand rate (TSR) which is the minimum sand rate necessary to achieve monitor output higher than the background noise level. A procedure has been developed to determine TSR for various multiphase flow conditions. The objective of the present research is to find the variation in threshold sand rates in different multiphase flow regimes while varying the sand size from 25 to 300 µm. Some examples are shown for several different flow conditions utilizing two different acoustic monitors in multiphase flow loops with different pipe diameter sizes in vertical and horizontal orientation. Water and air are used as fluids. Several experiments with various gas-liquid flow velocity combinations were performed, and acoustic data have been gathered with various sand rates to observe the effects of the multiphase flow regime on threshold sand rates. These results are compared to the previously obtained test results on 76.2 mm (3-inch) and 101.6 mm (4-inch) ID test loops. The results from this work can help operators understand how acoustic monitors can detect and distinguish sand impact noise from the background flow noise in multiphase flow. In this way, a greater assurance is provided to operators for optimizing oil and gas production rates, especially in wells that have a tendency to produce sand.