Highly constrained low level fluid sensing in process pipes utilizing non-invasive ultrasonic methods

Abstract

Determination of the presence of hazardous waste in sealed pipes is a major issue of concern in many industries. Typically, when hazardous process piping needs to be opened, it is very difficult to truly know whether the pipe is empty, and thus free of hazardous material. Therefore, standard procedure is to assume worst case scenario and dedicate significant resources to Hazmat teams and containment when opening the piping or preparing it for decommissioning. In this work, we explore three separate ultrasonic-based techniques for very low-level fluid sensing in process piping. It was found that ultrasonic techniques suffer from several issues, including guided wave contamination, local resonance, overlap from other echoes, and more. To overcome these issues, three separate techniques were explored, including pulse-echo with subtraction, total focusing method (TFM) imaging, and another technique that exploits the local resonance of the pipe when it is fluid-loaded. It was found that, with proper calibration and signal processing, pulse-echo is an easy-to-use technique down to relatively low fluid levels. However, the best performance came from modified total focusing method imaging, which could detect extremely low fluid levels while being robust from false negatives (detecting no waste when there was waste).