Experimental Validation of a Fast Forward Model for Guided Wave Tomography of Pipe Elbows

Abstract

Ultrasonic guided wave tomography (GWT) methods for the detection of corrosion and erosion damage in straight pipe sections are now well advanced. However, successful application of GWT to pipe bends has not yet been demonstrated due to the computational burden associated with the complex forward model required to simulate guided wave propagation through the bend. In a previous paper [Brath et al., IEEE Trans. Ultrason., Ferroelectr., Freq. Control, vol. 61, pp. 815-829, 2014], we have shown that the speed of the forward model can be increased by replacing the 3-D pipe bend with a 2-D rectangular domain in which guided wave propagation is formulated based on an artificially inhomogeneous and elliptically anisotropic (INELAN) acoustic model. This paper provides further experimental validation of the INLEAN model by studying the traveltime shifts caused by the introduction of shallow defects on the elbow of a pipe bend. Comparison between experiments and simulations confirms that a defect can be modeled as a phase velocity perturbation to the INLEAN velocity field with accuracy that is within the experimental error of the measurements. In addition, it is found that the sensitivity of traveltime measurements to the presence of damage decreases as the damage position moves from the interior side of the bend (intrados) to the exterior one (extrados). This effect is due to the nonuniform ray coverage obtainable when transmitting the guided wave signals with one ring array of sources on one side of the elbow and receiving with a second array on the other side.

Scattering of guided waves propagating through pipe bends based on normal mode expansion

“…(19) and (24) and considering the continuity principle of Eq. ( 18), we obtain Equation (26) gives the relationship between the expansion coefficients as which can be expressed in matrix form as…”

“…Similarly, Wu et al 24,25 used a magnetostrictive system to study scattering of the L(0,1) and T(0,1) modes passing through pipe bends. Brath et al 26 experimentally mapped the pipe elbows with a fast forward model-based guided wave tomography method.…”

Efficient Guided Wave Modelling for Tomographic Corrosion Mapping via One-Way Wavefield Extrapolation

“…Multiple dispersive Lamb modes in pipes of varying thickness complicate matters, causing interference at the receiver. Therefore, efforts usually prioritise lower frequencies, focusing on fundamental Lamb modes like the symmetric ( and asymmetric ( modes due to their manageable dispersion [ 3 , 27 , 43 ].…”

Least-squares reverse time migration (LSRTM) for damage imaging using Lamb waves

“…Excitation or reception components can be piezoelectric wafers [7,8], shear-horizontal transducers [9,10], polyvinylidene difluoride (PVDF) transducers [11], air-coupled transducers [12,13], pulsedlaser [14] and laser Doppler vibrometer (LDV) [15]. The patterns for transducer distribution vary from sparse array [16] to densely distributed arrays [17,18], and full-aperture array [19,20].…”