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 and local measurements even when this is done risk based, because some corrosion processes behave unpredictable. This paper demonstrates a system that monitors the wall thickness of pipe lines over large areas in an economical attractive way using a limited number of low-power ultrasonic transducers. By applying tomographic inversion to the travel time of guided 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 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 performance and it will give an outlook of the possible applications and possibilities to integrate other functionality like crack monitoring with the same system.

In this paper there will be a focus on applying this concept in new build installations because of the low additional costs involved when applying the sensors while manufacturing the assets. This makes it very attractive for remote oil and gas production installations. However, it has been shown that it can save costs also for existing installations by replacing inspections at sections of installation, which are not piggable and difficult to approach. This is in general the case in oil and gas (offshore) production installations. Cost of inspection projects are extremely high in off shore environments and saving one inspection job can probably guarantee already your return on investment. Next, when using this technique it will also allow to make a wall thickness map of areas that are not accessible by current inspection techniques like corrosion under supports and feed through.

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