The Case for Clamp-on Flow Meters: Part 3
By Thomas Michalowski
Clamp-on Ultrasonic Flow Meters
Clamp-on ultrasonic flow meters do not achieve the accuracy of the highly accurate in-line transit-time meters used, for example, for custody transfer fiscal calculation in the oil and gas industry. This is mainly due to attenuation in the pipe wall and liner, material buildup within the pipe bore, pipe centricity and other reasons. Even so, clamp-ons can achieve accuracy better than 0.5%, although in general practice, +/- 0.5% to +/- 2.0% is the norm. They do offer excellent repeatability at around 0.2% to 0.3% and are extremely reliable. But the major benefits of ultrasonic clamp-on flow meters are their versatility and cost effectiveness.
• They can be used in non-conducive fluids, gases and steam.
• Being non-intrusive, they do not cause a pressure drop.
• They reduce disruption during installation because there is no need to shut down the process or cut into the pipe.
• They have no moving parts, for a long working life.
• They require no periodic calibration.
• They can measure both low and high flows
• They can operate in harsh and hazardous environments.
• They are easy to use.
• Data transfer is easy, via optional outputs.
• They have a low capital cost compared with other technologies.
• One clamp-on meter can be used on a variety of
• Additional analog inputs for temperature transmitters allow measurement of energy flow rate in liquids.
• Optional dual-channel/dual-path models can measure flow in two separate pipes using just one measuring unit and two sets of transducers.
• Portable versions provide easy, temporary checks of processes or of existing in-line meters.
Focus on User-Centered Design
The development of new clamp-on flow meters puts the user at the center of the design process. Not only do new designs improve technology, but they also consider the strengths and limitations of users and anticipate how users deal with the daily realities of their jobs. Developing new products requires observing, measuring and validating how people use those products. GE supports this sort of research, working with industrial designers and researchers to help its engineers working on new product design understand the challenges that customers face. This research contributes to design decisions clearly rooted in people, their processes and their goals.
Applications of Clamp-on Ultrasonic Flow Meters
Clamp-on ultrasonic flow meters measure a wide range of fluids, including liquids such as:
• Ultra-pure water.
• Clean liquids.
• Sewage and wastewater.
• High viscosity liquids.
• Corrosive liquids.
• Abrasive liquids.
• Hydrocarbons, including high-temperature, high-pressure pulsating and low speed liquids. Some gases suitable for clamp-on ultrasonic flow metering include:
• Superheated steam.
• Natural gas.
• Compressed air.
• Nitrogen and oxygen.
Clamp-ons can also differentiate between the different fluids that are sometimes carried by the same pipeline, as often happens in the petroleum industry. Clamp-on ultrasonic flow meters have three main applications. First, as in situ or fixed installation, flow meters. Secondly, as check flow meters to evaluate the correct functioning of existing flow meters. And thirdly, as versatile multi-purpose flow meters that can be moved around a plant or installation to gather flow meter data as required. These applications apply to
both liquid and gas flow metering.