Traditional inline inspection tools use odometer wheels to determine the distance travelled through the pipeline and thus the location of identified defects. In addition, typically above ground markers (AGMs) are used to confirm and potentially correct for the odometer wheel distances. This paper will address methods to accurately determine the location of defects identified in a pipeline by a free-floating unconventional ILI tool without the need for above ground markers, odometer wheels, or similar devices.
This can be achieved by combining sensor readings from an inertial measurement unit, magnetometers, and a pressure sensor, while realizing that fluid transport through a pipeline limits the number of degrees of freedom and making use of pipeline characteristics.
Different scenarios will be discussed depending on the deployment method and available information. The details of the steps in determining the distance will be outlined and compared to truth data of the identified defect. It will be illustrated that in all cases a location accuracy of plus or minus 20 foot is reached.