Corrosion Mapping Using Ultrasonic Guided Wave Tomography
报告人：范峥博士（Dr. Zheng Fan)
---Nanyang Technological University,Singapore
Prof Zheng Fan obtained his PhD degree at Imperial College London, specialized in Non-Destructive Evaluation (NDE). He is currently an assistant professor in the school of Mechanical and Aerospace Engineering at Nanyang Technological University in Singapore, leading a research team with 16 people including PhD students and postdoctoral fellows. The research focus of his team is to develop novel NDE techniques for metal and composite inspection, structure health monitoring and material characterization, by integrating physics and modeling techniques with the development of rapidly exploitable technologies. He has collaborated with varies industries including Rolls-Royce, Shell, Lloyds Register, Sembcorp etc for different research and consultancy projects. His research work has gained worldwide recognition, and he has recently been appointed as an Associate Editor to “Ultrasonics” – one of the top-tier journal published by Elsevier in this field.
Corrosion of pressure vessels, storage tanks and pipelines is a significant problem in petrochemical and nuclear industries. Detecting and quantifying the wall thickness loss due to the corrosion damage is of growing interest.Conventional ultrasonic thickness-gauging methods are tedious and expensive, especially for inaccessible areas. Guided wave tomography offers good potential to monitor the remnant thicknesses of corrosion patches without accessing all points on the surface. It uses the dispersion characteristics of guided waves, and reconstructs the thickness map by the inversion of ultrasonic signals captured by a transducer array around the inspection area.
This work applies a novel guided wave tomography method based on full waveform inversion (FWI) for the corrosion mapping. It uses a numerical forward model to predict the scattering of guided wave through corrosion defects, and an iterative inverse model to reconstruct the corrosion profile. At each iteration, numerical modeling is performed with the aim of least-squared minimization of the misfit between the modeled and the observed data. The FWI algorithm allows higher order diffraction and scattering to be considered in its numerical solver, thus can provide accurate inversion results. Numerical simulation and experiment have been carried out to validate the algorithm, showing excellent agreements. A guided wave tomography system is then designed to monitor different stages of forced electrochemical corrosion. The reconstructed thickness map match perfectly with the prediction using the Faraday’s Law, as well as the measurements from a laser profilemeter.