Opportunities for Permanent Corrosion Monitoring of Pipelines Using Guided Wave Tomography

Corrosion and erosion are two major degradation mechanisms of piping systems and pipelines that both lead to wall thickness loss. To ensure sufficient integrity levels of these assets NDE is currently conducted at time based intervals often associated with shut downs. However, both economical and social requirements are pushing the industry to higher levels of availability, reliability and safety of installations at minimum costs. Using permanent sensors that continuously monitor the wall thickness of assets over large areas allows improvement of the availability of installations at lower inspection costs. Because when inline data is continuously available the maintenance can be planned (just) in time at the most optimal moment. Therefore, the permanent sensors will save inspection costs and minimize unplanned maintenance. This can not be achieved with the current method of periodic inspections even when this is done risk based, because some corrosion processes behave unpredictable. This paper demonstrates a system which is able to monitor the wall thickness of pipe lines over large areas in an economical attractive way using a limited number of low-power ultrasonic transducers. The transducers excite specific guided wave modes with a phase velocity that strongly depends on the wall thickness. By applying tomographic inversion to the travel time of these wave modes along different paths, a wall thickness map with 100% coverage can be obtained. Experimental results on a 10^″ steel pipe with a wall thickness (WT) of 8 mm show that this system is able to detect and size defects with a depth of 10% and diameter of 15 cm. The area covered in this case was the complete wall of a pipe with a length of 4 m. This paper further explains the advantages and the performance of this system. Furthermore, it will give an outlook of the possible applications.