Detection of anomalies inside hollow metal cylindrical structures

The evaluation of the physical conditions of a hollow metal cylindrical structure is critical in many applications, such as those involving oil or power generating industries or water pipeline networks. Direct and internal inspection is often not possible or highly costly in terms of time and inspection tools. We present here a guided waves-based technique whose particularity is to detect and to quantify a circular anomaly inside a hollow metal cylindrical structure, while being deployed. The technique requires only one measurement point to obtain information on remote sections that are hundreds of metres apart. Radar equipment sends an electromagnetic wave through an open end of the structure and it receives the backscattered field, which is produced by variations of the internal hollow structure radius (deformations, welding joints, etc.). We derive the link between the recorded signal, which carries information on amplitude and propagation time, the circular anomalies parameters, defined by the percent radial reduction, rap, and the deformation length, la, avoiding the complications of the most classification algorithms. The anomaly identification is obtained through an inversion procedure that performs well with both the synthetic and real data. In the latter case, the estimated parameters of a given anomaly ( ^rap ¼4.9%, ^ la ¼3.85 m) are in good agreement with the actual ones (rap¼5%, la¼3 m).