Influence of steel wrapping on magneto-inductive testing of the main cables of suspension bridges

The number of structurally deficient or functionally obsolete bridges is likely to increase in coming years due to continued bridge aging and deterioration and a decrease in funding needed to maintain and repair these structures. In the case of suspension bridges, problems arise due to corrosion and wire breaks within the main cables of the bridge. The magnetic flux leakage (MFL) method has been known for many years and is used for inspection work in different fields, such as the non-destructive evaluation (NDE) of pipelines, arial tramways or stay cable bridges. A special characteristic of the main cables of suspension bridges is the presence of steel wrapping, which is used to compact the cable and hold it in shape. If a NDE by means of magnetic methods is performed on such a cable, disturbances due to the wrapping can be expected in the measured signal. Furthermore, the very large diameters of these cables (up to 500 mm) poses an unsolved challenge in the application of magnetic non-destructive testing methods.The finite element method (FEM) and other simulation techniques are widely used in any field of engineering. The possibility to simulate different scenarios and the ability to quantify physical properties at any position where real measurements cannot be performed are among the main advantages of such methods. In this work, a FE model is presented to investigate the influence of the steel wrapping on MFL data. After the characterization of the disturbance, a postprocessing algorithm to eliminate the disturbances is discussed. Further, boundary conditions for a successful application of the proposed method in a real application are formulated.