Characterisation of steels with microdefects using a laser interferometry technique

Low microdefect level is essential for ensuring the performance of material. Early detection of microdefect areas allows the estimation of the residual life of constructions and prevents catastrophic failures of components. Ultrasound laser interferometry provides a unique inspection method that enables the study and visualisation of the processes of elastic wave interaction with microdefects embedded in solids, in a non-contact way. In the present paper, the distribution of acoustic fields on the surface of the metal disks obtained was investigated with the use of a laser Doppler interferometer. Specimens containing micropores, cut from the bent section of a steam pipeline that had been subjected to long-term operation at a heat-electric generating station, were used for the studies. Various methods of data digital processing have been applied to trace changes in ultrasound beam energy distribution and geometrical parameters of ultrasound beam projection in case of the presence of microdefects.