Total Focusing Method (TFM) and Phase Coherence Imaging (PCI) applied to various industrial cases

Abstract

Imaging techniques based on ultrasonic Total Focusing Method (TFM1) are more and more applied for industrial applications. Adoption of the technique has been made easier with the publication of the revised ASME V and ISO 23864 and 23865 standards. TFM is an inspection technique that involves two steps: the first one is the data acquisition process called Full Matrix Capture (FMC) and the second one is the data reconstruction itself called TFM. TFM is able to focus the energy at every pixel within a region of interest providing a high-resolution image. Efforts have been made to improve the productivity of the technique using various excitation modes such as Plane Wave Imaging (PWI) to reach scanning speeds comparable to standard phased-array inspections while maintaining code compliance. While TFM is based on the extraction of the amplitudes of the FMC matrix, another technique called Phase Coherence Imaging (PCI2) uses the phase information from those signals. The PCI image shows high values when all the elements contribute in phase. This is the case for small diffractors that tend to send energy in all directions such as small cracks (HTHA, porosities…), tips from cracks and grain noise. At the opposite, specular echoes tend to be minimized since few elements contribute to the echo. In this paper, we’ll show the advantages of both techniques on various industrial cases.