Ultrasonic Flow Metering (UFM)
Ultrasonic Flow Metering (UFM) is a valuable method of recording the circulation conditions of a boiler. Analysis of the UFM data provides insight into the workings of the steam system and can highlight deficiencies such as side-to-side imbalances, low velocities that may cause departure from nucleate boiling, steam carryunder and inadequate overall circulation ratio.
UFM makes direct water velocity measurements in selected downcomers and boiler furnace tubes without penetrating the pressure part boundary, eliminating the boiler downtime required to install pitot tubes. It can also detect the reversal of flow, and its cross-pipe line-scan sensor produces more accurate data than a single-point pitot measurement. The UFM measurements provide actual measurements of flow velocities in certain circuits whose results are utilized to fine tune and improve the accuracy of our evaluations of natural circulation conditions in boilers.
UFM is used successfully for making flow measurements on tubes and pipes with diameters from 2½ inches to 22 inches, water velocities from less than 0.1 feet/second to over 14 feet/second, and at temperatures up to 600°F/316°C.
A typical circulation evaluation that uses UFM measurements has the following elements:
- Description of boiler circuits.
- Background on circulation criteria.
- Description and limitations of circulation calculations.
- Average steam content of mixture leaving the boiler circuits (circulation ratio).
- Average tube entrance velocities in the boiler circuits.
- Steam flow and temperature.
- Steam separating capacity of the drum.
- An inadequate overall circulation ratio.
- Natural circulation conditions in boilers.
- Temperatures up to 600°F/316°C.
