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First Field Results of Guided Wave Tomography for Continuous Monitoring of Corrosion and Erosion Damage in Pipelines



The effective life management of pipelines in the Oil and Gas industry requires monitoring techniques that can probe an extended section of a pipe and can sample its state with relatively high frequency so as to implement corrosion mitigation in a timely fashion. Due to the typically low corrosion rates, 1 mm/yr or less, the monitoring technique must be sensitive to wall-thickness changes that are in the order of a few tens of micrometers. Ultrasonic guided wave tomography (GWT) with permanently installed sensors offers an attractive compromise between sensitivity and area coverage by combining the long range propagation characteristics of guided ultrasonic waves with the principles of model-based inversion. Here, the pipe section to be monitored is delimited by two ring arrays of ultrasonic transducers that encircle the pipe and measure guided wave signals after traveling inside the pipe wall from one array to the other. The signals are interpreted by advanced GWT algorithms to form a wall thickness map of the entire pipe section. In this paper we review the principle of operation of GWT, discuss its performance, and present the first long term field results obtained for a pipe in a deepwater rig in the Gulf of Mexico. The field results show that GWT based on EMAT transduction provides highly stable wall thickness estimations even in the presence of multiphase flow inside the pipe undergoing a wide range of pressure and temperature fluctuations.


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