Enhancing the Ability in Detecting Defects Occurred in Covered Pipe by using Matching Pursuit and Smooth Empirical Mode Decomposition

Pipes that carry gas into residential buildings are one of the most important infrastructures in cities. These pipes are prone to corrosion after a period of time because of different environmental factors. In order to avoid any pipe rupture that may cause explosion, the integrity of such pipes much be checked on a regular basis. Ultrasonic guided wave is an effective method for structural health monitoring of plate like structures and pipes. However, the signals that are obtained from guided waves can be very difficult to interpret due to mode conversion, overlapped modes and dispersion effect. In order to extract meaningful information of guided wave signals, using advanced signal processing methods are inevitable. The problem of dispersion effect is taken care by the method called matching pursuit. The separation of overlapped modes is contributed by another method called smooth empirical mode decomposition. Dispersion means that the velocity of the propagating wave is a function of its frequency. As in most guided wave applications in pipe inspection, narrowband tone-burst excitation signal is commonly used, dispersion causes guided wave signal to spread in time axis as it travels and changes its shape. Matching pursuit is a greedy algorithm that can be used to approximate signals. This method iteratively approximates a signal by its predefined dictionary. The waveforms predicted by matching pursuit have the maximum resemblance with real GW signals. Hence, the true defect related signals can be identified even after the consideration of mode dispersion. The smooth empirical mode decomposition combines the methods of empirical mode decomposition and wavelet transform. It is used to expose a natural corrosion hidden in highly overlapped and the contaminated signals generated from the propagating guided waves in a concrete covered pipe. The validation of the above proposed methods had been verified by both simulation and experimental results that were tested on real concrete-covered pipes.