Pipeline long-range inspection and monitoring by an innovative magnetic collar for magnetostrictive guided-wave systems

In this paper, a new system for pipeline long-range inspectio n and monitoring is described. The system is based on a set of local magnetostrictive sensors surrou nding the inspected pipeline. The local signal acquisition allowed by each individual sensor and the subse quent detection process makes possible a better identification and classification of flaws and t heir geometrical characterization. In addition a software packet that includes algorithms for flaw recogniti on was developed. Finally, an experimental campaign to test and validate the new system and software is presented. 1. Background Corrosion and defects in pipelines are general problems, pa rticularly in the oil, gas, petro-chemical industries and for the water and gas distr ibution. Since a significant percentage of industrial pipelines are insulated, this me ans that even external corrosion cannot readily be detected without the removal of the insu lation, which in most cases is prohibitively expensive. Moreover, in the case of inacces sible pipelines, visual or conventional non-destructive inspection can become very expensive, thus an important inconvenient. Furthermore, a technique capable to perform in-service inspec tion would be greatly useful for continuous cycle plants as the petro-chemical ones (1), (2). In this paper the attention is focused on long-range guided wa ves (GW) used for the rapid survey of pipes and plates, for detection of both internal and external corrosion (3). These waves are characterized by relatively low frequenc ies (typically under 200 kHz) and can propagate over long distance (tens of meters) in any bounded structural parts, including rods, pipes, and plates (4). The main attraction of long-range guided wave inspection i s that it allows a large area of structure to be tested from a single transducer posit ion, thus avoiding the time consuming scanning required by conventional ultrasonic or edd y current methods. The technique becomes even more attractive if part of the st ructure to be tested is inaccessible, for example a road-, river- or railway-cro ssing . The test is usually done in pulse-echo mode, the transducer transmitting the guided wave along the structure. Returning echoes indicate the presence of defects or othe r structural features. This technology performs 100-percent volumetric examination of a large area of a pipe and detects and locates both internal and external defect s in the sections around the test position. Fig. 1 sketches the basic elements of the guided wave te chnology applied to the piping system inspection.