This paper aims to provide an overview of the experimental and simulation works focused on the detection, localisation and assessment of various defects in pipes by applying fast-screening guided ultrasonic wave techniques that have been used in the oil and gas industries over the past 20 years. Major emphasis is placed on limitations, capabilities, defect detection in coated buried pipes under pressure and corrosion monitoring using different commercial guided wave (GW) systems, approaches to simulation techniques such as the finite element method (FEM), wave mode selection, excitation and collection, GW attenuation, signal processing and different types of GW transducers. The effects of defect parameters on reflection coefficients are also discussed in terms of different simulation studies and experimental verifications.

Detection, Localisation and Assessment of Defects in Pipes Using Guided Wave Techniques: A Review.

A pseudospectral model of linear elastic wave propagation is described based on the first order stress-velocity equations of elastodynamics. k-space adjustments to the spectral gradient calculations are derived from the dyadic Green's function solution to the second-order elastic wave equation and used to (a) ensure the solution is exact for homogeneous wave propagation for timesteps of arbitrarily large size, and (b) also allows larger time steps without loss of accuracy in heterogeneous media. The formulation in k-space allows the wavefield to be split easily into compressional and shear parts. A perfectly matched layer (PML) absorbing boundary condition was developed to effectively impose a radiation condition on the wavefield. The staggered grid, which is essential for accurate simulations, is described, along with other practical details of the implementation. The model is verified through comparison with exact solutions for canonical examples and further examples are given to show the efficiency of the method for practical problems. The efficiency of the model is by virtue of the reduced point-per-wavelength requirement, the use of the fast Fourier transform (FFT) to calculate the gradients in k space, and larger time steps made possible by the k-space adjustments.

A first-order k-space model for elastic wave propagation in heterogeneous media.

The main goal of this work is to give a review of the Perfectly Matched Layer (PML) technique for time-harmonic problems. Precisely, we focus our attention on problems stated in unbounded domains, which involve second order elliptic equations writing in divergence form and, in particular, on the Helmholtz equation at low frequency regime. Firstly, the PML technique is introduced by means of a simple porous model in one dimension. It is emphasized that an adequate choice of the so called complex absorbing function in the PML yields to accurate numerical results. Then, in the two-dimensional case, the PML governing equation is described for second order partial differential equations by using a smooth complex change of variables. Its mathematical analysis and some particular examples are also included. Numerical drawbacks and optimal choice of the PML absorbing function are studied in detail. In fact, theoretical and numerical analysis show the advantages of using non-integrable absorbing functions. Finally, we present some relevant real life numerical simulations where the PML technique is widely and successfully used although they are not covered by the standard theoretical framework.

Perfectly Matched Layers for time-harmonic second order elliptic problems

A signal processing approach to exploit chirp excitation in Lamb wave defect detection and localization procedures

A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments.

A dispersion compensation procedure to extend pulse-echo defects location to irregular waveguides

The WKB method applied to the reflectiontransmission by a depth-varying random distribution of cylinders in a fluid slab-like region.- Advances in ultrasonic testing of austenitic stainless steel welds. Towards a 3D description of the material including attenuation and optimisation by inversion.- Imaging of defects within austenitic steel welds using an ultrasonic array.- Materials and mechanical aspects of bonded joints.- The causal differential scattering approach to calculating the effective properties of random composite materials with a particle size distribution.- Modelling of scattering of ultrasounds by flaws for NDT.- Finite element computation of leaky modes in stratified waveguides.- Ultrasonic bulk wave propagation in concentrated heterogeneous slurries..- Dynamics of elastic bodies connected by a thin adhesive layer.- Acoustic wave attenuation in a rough-walled waveguide filled with a dissipative fluid.- Some advances towards a better understanding of wave propagation in civil engineering multiwires trands.- A numerical method for the simulation of NDT experiments in an elastic waveguide.- Finite elements for a beam system with nonlinear contact under periodic excitation.- Nonlinear acoustic fast and slow dynamics of damaged composite materials: correlation with acoustic emission.- Asymptotic expansions of vibrations with small unilateral contact.- Propagation of compressional elastic waves through a 1-D medium with contact nonlinearities.- 3D Finite Element simulations of an air-coupled ultrasonic NDT system.- The reverse time migration technique coupled with finite element methods.- Modelling of corner echo ultrasonic inspection with bulk and creeping waves.- Attenuation of Lamb waves in the vicinity of a forbidden band in a phononic crystal.- 3D orthogonality relations for the surface waves and the far field evaluation in viscoelastic layered solids with or without fluid loading.- Damage detection in foam core sandwich structures using guided waves.- Sensitivity of the guided waves to the adhesion of lap joints: Finite Element modeling and experimental investigations.- Guided waves in empty and filled pipes with optimized magnetostrictive transduction.- Piezoelectric material characterization by acoustic methods.- Ultrasound characterization of aggregated red blood cells: towards in vivo application.- A 3D semi-analytical model to predict the behavior of ultrasonic bounded beam traveling in cylindrical solid bar embedded in a solid matrix..- Comparison between a multiple scattering method and direct numerical simulations for elastic wave propagation in concrete.- Investigation of a novel polymer foam material for air coupled ultrasonic transducer applications.- Dual signal processing approach for Lamb wave analysis.- Structural health monitoring of bonded composite patches using Lamb waves.- Simulation of structural noise and attenuation occurring in ultrasonic NDT of polycrystalline materials.- Ultrasonic array reconstruction methods for the localization and the characterization of defects in complex NDT configurations.- Investigation of damage mechanisms of composite materials: Multivariable analysis based on temporal and wavelet features extracted from acoustic emission signals.- Investigation of damage mechanisms of composite materials: Multivariable analysis based on temporal and wavelet features extracted from acoustic emission signals.- Propagation of elastic waves in a fluid-loaded anisotropic functionally graded waveguide: Application to ultrasound characterization of cortical bone.- Coherent wave propagation in solids containing spatially varying distributions of finite-size cracks.

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Marc Deschamps

Papers

Ultrasonic Wave Propagation in Non Homogeneous Media

Multiple Scattering in Periodic and Random Media: An Overview