Pipe inspection by cylindrically guided waves

Abstract

In this research the cylindrically guided wave inspection technique is proposed for detecting the anomalies in a pipe. Efficient inspection of pipelines for internal and external damages is a challenging task in the chemical and power industries where long pipelines are used and the pipes are coated by insulating materials. Under traditional methods insulation coatings are removed at selected places, then the pipe wall thickness at these spots is measured by ultrasonic transducers. This is a time-consuming and expensive operation since the operation requires point-to-point examination. Guided wave ultrasonics, proposed in this research, is a much more efficient technique because by this technique long pipes can be inspected by removing insulation at only limited places. Detecting anomalies inside the pipe wall at a specific depth can be realized by correctly selecting a cylindrical guided wave and propagating that mode through the pipe. A new transducer holder mechanism has been designed and fabricated for pipe inspection by cylindrical guided waves. A number of advanced coupling mechanisms developed recently for large plate and pipe inspection require the presence of a coupling fluid between the ultrasonic transducer and the pipe or plate specimen. These mechanisms can be used for inspecting horizontal pipes and plates. Commercially available ultrasonic transducers have been used to generate compressional ultrasonic waves in the coupling medium. Those waves are converted to cylindrical guided waves in the pipe by the new coupling mechanism. The new coupling mechanism presented in this research uses solid material as the coupler and can be used equally well for inspecting horizontal as well as inclined or vertical pipes. The new coupling mechanism has been designed to generate efficiently different guided wave modes in the pipe. Different kinds of anomalies in pipes have been successfully inspected. The preliminary results show that a number of Lamb modes when generated properly by the new coupling mechanism are very sensitive to pipe defects. These experimental results along with the new design of the coupling mechanism are presented in this dissertation.