Water Level Measurement in Vertical Pipe Based on Time-of-Flight Method of Lamb Wave

Liquid accumulation is frequently encountered in the long-distance coal-bed methane gathering and transportation pipelines. It will hinder the effective transportation of gas and accelerate pipeline corrosion. Therefore, accurate level measurement is essential for gathering pipelines. A time-of-flight (TOF) method for water level measurement in vertical pipe using ultrasonic Lamb wave is proposed. The influence of water level in vertical pipe on wave propagation is investigated. Finite element simulation and experiments confirm the significant difference in TOF for the Lamb wave to propagate in immersed pipes and in hollow pipes. There is a linear relationship between water level and TOF, which can be fitted with a linear function with a relative root mean square error of $9 \times 10^{-3}$. The results show that the average fitting error of the two-end calibration method is 6%. Therefore, the effectiveness of the TOF method is demonstrated.