Ultrasonic flowmeters are increasingly popular in oil measurement applications due to their non-invasive design, absence of moving parts, and ability to handle a wide range of pipe sizes and fluid types. These meters measure flow velocity by transmitting ultrasonic sound waves through the fluid and measuring the transit time difference between signals sent in the direction of flow and against it. This transit-time difference is directly proportional to the average flow velocity, which is then converted to volumetric flow rate. Modern multi-path ultrasonic meters use four or more paths to average out flow profile irregularities and achieve very high accuracy.
Clamp-on ultrasonic flowmeters are a popular variant that attaches externally to the pipe without requiring any cutting or welding. This makes them ideal for temporary measurement, flow surveys, or retrofitting to existing pipelines where installation downtime is not acceptable. However, clamp-on meters are generally less accurate than wetted (spool piece) ultrasonic meters and are more sensitive to pipe wall condition and coupling quality. For custody transfer and high-accuracy applications, wetted multi-path ultrasonic meters installed in dedicated metering runs are the preferred choice.
Ultrasonic flowmeters work best with clean, homogeneous liquids. In heavy crude oil or residual fuel oil applications, the high attenuation of sound waves in viscous fluids can reduce signal strength and accuracy. Some manufacturers offer low-frequency transducer options specifically designed for high-viscosity and aerated fluids. Unlike electromagnetic meters, ultrasonic meters work with non-conductive petroleum products and do not require the fluid to have any minimum electrical conductivity. Their output is unaffected by fluid conductivity or viscosity within their specified range, making them a versatile choice for many refined petroleum and light crude oil applications.