Abstract
Corrosion under insulation (CUI) is a common cause of pipeline failure in the oil and gas industry. Its detection with conventional inspection techniques is challenging due to the presence of the insulation layer and a protective metallic cladding that prevent direct access to the pipe surface. Currently, several techniques are being developed to detect sections of wet insulation since water is a necessary precursor to corrosion. Among these, guided microwave testing has been proposed as a cost-effective approach to screen an extended length of pipeline. The pipe and metallic cladding naturally form a large coaxial transmission line in which the insulation acts as a dielectric and supports the propagation of microwave signals. The inspection is performed by launching a microwave signal from an array of antennas permanently installed at one location along the pipeline. Wet insulation is then detected according to the radar principle; water results in the partial reflection of the incident microwave signal owing to the permittivity contrast between dry and wet insulation. This paper reviews the underpinning principles of long-range guided microwave testing and presents a new study aimed at demonstrating the sensitivity of the technique in the presence of complex water saturation gradients inside the insulation.
