Detection of Corrosion of Insulated Piping Using SH Angle Probe

One of the serious problems regarding insulated piping in petroleum and petrochemical plants is external surface corrosion. In general, visual inspection after removing insulation is carried out to detect corrosion. However, removing insulation is uneconomical, namely high cost, and time consuming processes are necessary such as setting up a scaffold. Ultrasonic guided wave technique has potential possibility to detect corrosion of long piping and has been recently investigated regarding its propagation characteristics. In this study, guided wave generated by horizontally polarized shear (SH) wave is applied to detect corrosion of insulated piping ranging from 1B to 3B. The reason why we select SH wave is that it has an advantage of being insensitive to internal fluid in piping. Through this study it is clear that SH guided wave is applicable to small diameter piping because sound beam of SH wave propagates along the longitudinal direction without circumferential extent. Accordingly local corrosion can be detected using SH guided wave technique.