Feasibility study of sludge and blockage detection inside pipes using guided torsional waves

The accumulation of sludge and blockages in pipes is a problem which affects many industries. It has been previously reported that in principle sludge and blockages can be detected and even characterized by using guided ultrasonic torsional waves, based on an idealized model in which the sludge layer was simplified in terms of geometry and material properties. The work revealed that the presence of a layer inside a pipe scatters the guided wave propagating in the pipe and both the reflection and transmission of the guided wave can be used to effectively detect and characterize the layer. Accordingly, two guided wave measurement techniques have been proposed. This paper proceeds the work by taking into account more realistic sludge characteristics, including irregular axial and circumferential profiles of the sludge layer, imperfect bonding state between the sludge and the pipe and the material damping of the sludge. The influence of these issues is investigated to identify the critical factors that influence the detection and characterization capability of the two measurements. The study shows that both reflection and transmission measurements can be exploited usefully and non-intrusively to detect realistic accumulations of sludge and blockages; however, the quantification of such materials will be difficult due to their arbitrary shape and properties.