​Conventional ultrasonic inspection techniques cannot get around structural obstacles, making some areas of​ the pipes inaccessible. List, a CEA Tech institute, is investigating a workaround that involves combining—for the first time ever—two different guided-wave techniques.

The researchers developed a novel and very promising method that uses the propagation of two types of high-frequency waves in the part being inspected. The resulting alternating propagation pattern effectively renders the obstacle "invisible" to the waves. The researchers then used the method to inspect the part for structural integrity. "We decided to use a 'mode conversion' pipe-wall thickness-loss detection technique based on an analysis of the changes to the wave as it passes through the part being inspected," explained a List researcher. Each component of the new method was tested separately to ensure effectiveness. And the combined approach is currently being tested in the lab to see if it can pick up thickness-loss-type defects, such as those due to corrosion, in areas of piping "hidden" behind an obstacle.

The results of the research are being assessed in a simplified configuration under a partnership with French electric utility EDF. The assessment could bring operationally-ready ultrasonic non-destructive testing methods to all industries that need to monitor difficult-to-access pipework.