Abstract
The monitoring of liquid-filled tubes with respect to the formation of soft deposition layers such as biofilms on the inner walls calls for non-invasive and long-term stable sensors, which can be attached to existing pipe structures. For this task a method is developed, which uses an ultrasonic clamp-on device. This method is based on the impact of such deposition layers on the propagation of circumferential guided waves on the pipe wall. Such waves are partly converted into longitudinal compressional waves in the liquid, which are back-converted to guided waves in a circular cross section of the pipe. Validating this approach, laboratory experiments with gelatin deposition layers on steel tubes exhibited a distinguishable sensitivity of both wave branches with respect to the thickness of such layers. This allows the monitoring of the layer growth.
Highlights
In the process industry as well as in water-supply systems soft deposition layers within liquid-filled tubes such as biogenic coatings may cause serious degradations of the process performance and health problems [1,2]
In view of practical applications at existing tube installations, this paper shows another solution using single-phase transducers in a detachable clamp-on arrangement for circular steel tubes and circumferential leaky Lamb-type guided waves
In order to provide a sound baseline for investigations of the influence of deposition layers on the propagation of acoustic wave pulses, a thorough characterization of the wave pulse propagation in empty and water filled test tubes was necessary
Summary
In the process industry as well as in water-supply systems soft deposition layers within liquid-filled tubes such as biogenic coatings may cause serious degradations of the process performance and health problems [1,2]. Sensors for the long-time online-monitoring of the formation of such deposition layers are highly desired [3,4,5]. Ultrasonic detection methods such as ultrasonic time-domain or frequency-domain reflectometry allow the detection of the initial phases of biofilm formation with high sensitivity [6,7], but these methods are not suited for online applications. Sensor elements based on surface acoustic waves (SAW sensors) have proven to be sufficiently sensitive for biofilm detection as well, since their displacement field is localized at the solid-liquid interface and their propagation properties are strongly affected by the formation of such layers there [8,9]. One has to be aware that in liquid-filled tubes with metallic walls Lamb wave modes and similar wave modes with
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