Extracting Quantitative Information on Pipe Wall Damage in Absence of Clear Signals From Defect

Abstract

It has been well established that guided waves are sensitive to structural damages encountered on their path of propagation and for this reason this technique is very efficient for distinguishing defective structural components from defect-free ones. Although the guided wave technique can identify a specimen having a distribution of defects, detecting and quantifying a small defect on its path from a long distance, as required for structural health monitoring (SHM) applications, is not an easy task for the guided wave inspection technique even today, especially when the transducers cannot come in direct contact with the pipe wall. The current technological challenges for pipe inspection by generating guided waves using noncontact transducers are to detect a small defect on the pipe wall and estimate its location and size from a long distance when the reflected signal from the defect cannot be clearly identified as is the case for low frequency guided waves that can propagate long distances. Electro-magnetic acoustic transducers (EMATs) are used here to generate guided waves in the pipe by the noncontact technique. This paper shows how small a defect in a pipe wall can be detected and its location and dimension can be estimated using relatively low frequency guided waves generated and received by EMATs even when the defect signal is not clearly visible in the time history plot because various wave modes reflected from the defect and pipe ends overlap.

Integral structural health and load monitoring of a helicopter tail boom manufactured from aluminum sheet metal with support from frames and stringers by guided ultrasonic waves

“…The materials dynamic softening and geometrical stiffening by applied stress, both observed for Lamb waves, represent novel effects concerning SHM. The here reported results are part of developments and respected applications based on TOF monitoring for structural health and load monitoring [3][4][5][6][7]). …”

Detection and quantification of pipe damage from change in time of flight and phase

“…For this computation the pipe dimensions considered are outer radius 2.1 cm and inner radius 1.6 cm, same as the pipe inspected experimentally. The P (Longitudinal) and S (Shear) wave speeds in steel are 5.96 km/s and 3.26 km/s, respectively [13,14]. The computed group velocity dispersión curves of the longitudinal wave modes L(0, 1) and L(0, 2) are shown in and L(0, 2) modes can be generated in the pipe specimen by an ultrasonic transducer operating in the frequency range 50-175 kHz.…”

“…Velocity values in the pristine specimen were obtained from the group velocity dispersion curves [13,14], see Fig. 1 …”

“…Displacement fields generated by waves propagating in cylindrical geometries have been computed [4][5][6][7][8][9]. Guided waves have been used for crack and corrosion detection in pipes [10][11][12][13][14]. Most research focused on examining the effect of damage on the strength of the waves propagating through the specimen.…”

“…(Left) group velocity and (right) TOF as a function of frequency for the two wave modes L(0, 1) and L(0, 2) propagating in the steel pipe[13,14].…”