Direct Observation of Odometer Trajectory When Passing over Weld in Oil and Gas Pipeline

An odometer is an important part of a pipeline inspection gauge (pig) for measuring distance and defining the position of pipeline defects. Due to the peculiarity of their construction, odometers are prone to unbounded cumulative errors during pigging, and the weld is the main reason for this type of error. As a result, research on the odometer's motion when passing over a weld is essential for improving its accuracy and has attracted much more attention than before. In this paper, the trajectory of an odometer crossing over a weld was directly observed by a high-speed camera, and different trajectories with variations in translational velocity were proposed based on the experimental results. The effects of translational velocity, pretightening force, and spring rate on the odometer's trajectory were investigated. Experimental results indicate that a bouncing phenomenon occurred at a high translational velocity. A secondary jump, third jump, and even more jumps can be observed with increments of translational velocity. High pigging velocity can increase odometer error due to a serious collision, but this error can be restrained by a large pretightening force. Compared with the translational velocity and pretightening force, the spring rate has almost no influence on the odometer's error due to limited spring compression. Research results in this paper can provide better understanding of the motion of the odometer and contribute to finding a way to improve the accuracy of the odometer wheel system. (C) 2018 American Society of Civil Engineers.