Investigating the effect of coating thickness on detection of disbonding of large-diameter pipe coating using guided Lamb waves

Coated pipes are used in corrosive conditions such as water and soil. This paper presents an effective method to study the effect of coating thickness on detection of disbonding of pipe coating. In this regard, finite element modeling of ultrasonic guided Lamb wave propagation is conducted in order to study this defect. In order to simulate guided wave propagation in a pipe, a two-dimensional model can be employed as it is used for plates when the thickness-to-radius ratio of the pipe is less than 0.1. Therefore, two-dimensional finite element modeling of steel pipe coated with epoxy has been conducted in this paper. Second mode of Lamb wave (m2) in the bilayer plate has been generated at a suitable frequency. In order to model the disbonding of pipe coating, a specified condition is applied in the place of disbonding. Reflected signals from the disbonding are received by a sensor. Reflections and many mode conversions at beginning and end of the disbonding are seen resulting in disbonding detection. Coating thickness affects the probability of detection of this defect.