Detection of Hidden Corrosion in Pipes Carrying Gas into Hong Kong Residential Buildings by Ultrasonic Guided Waves and Advanced Signal Processing Technique

Pipes are widely used in infrastructures for delivering water, chemical and gas. Pipes carrying gas into residential buildings pass through concrete walls. Due to humidity in the atmosphere, they are prone to developing corrosion. However, the early detection of corrosion on the sections that are covered by concrete or soils is nearly impossible. If severe corrosion is allowed to continually occur, it may cause pipe rupture and consequently explosion and a catastrophe in which individuals’ lives are in high risk. To avoid such disaster early detection of corrosion in pipes are of vital importance. To facilitate early detection of corrosion occurring in these partially covered pipes, we investigated the capability of guided waves (GWs) in detecting defects through analysing the received GWs’ signals that were reflected by various defects. Although GW had found to be effective in locating defects and estimating the extent of corrosion, a proper signal processing tool must be used to extract defects related features from blurred signals due to noise and undesired GWs mode conversion. This paper reports the uses of GWs-based method to detect the defects and the Smooth Empirical Mode Decomposition (SEMD) to recover vital defect related features from corrupted GWs signals. With the help from SEMD, noise and undesired modes have been significantly minimized. A real case study was presented to illustrate the effectiveness of GWs and SEMD that the entry and the exit of the section of the pipes that are covered by concrete section can be clearly identified. Most importantly, the defects located within the concrete covered section can also be clearly revealed. The experimental results prove that the GWs inspection method with SEMD can efficiently detect corroded areas even they are covered by concrete that no conventional NDT methods are possible to detect each defects inside the concrete/soil covered sections.