Application of Nonlinear Guided Waves for Detecting Loose Flanged Bolted Joints in Pipelines

Guided waves are finding more applications for structural health monitoring of pipelines and other long, slender structures, particularly in the areas of corrosion and crack detection. Bolted joints are widely used in engineering structures in oil and gas, aerospace and civil structures. In practice, pipes with bolted joints are subjected to a variety of failure modes, including self-loosening, slippage, shaking, fatigue cracks and breakage. Guided waves technique is one of the promising techniques for detecting various damage types in pipelines, such as fatigue crack, impact damage, notches, holes and imperfect bolted joints. Guided waves technique for pipelines, involves transmitting guided waves along the pipe length. Using this method a relatively large region of pipe can be inspected from a single location. The system has the ability to transmit waves from a remote single location of the pipe and inspect inaccessible areas, such as road crossings and insulated pipes without causing any damages. The technique is especially sensitive for detection of damage in pipes. This technique allows a rapid screening of the all pipe; screening tools for fast assessment of large parts of installations shown to have a growing inspection potential. However most of linear guided waves techniques rely on baseline data which is the major drawback of the technique. In this paper a base line free approach is used to detect the imperfect bolted joints in pipelines using nonlinear guided waves. It is shown that imperfect joints generate contact acoustic non-linearity (CAN) which is a good indicator. The study shows that nonlinear wave packs carry important information about the quality of bolted joints in pipelines.