Magnetic Flux Leakage Testing Method And Tool For Broken Wires In Parallel Wire Cables In Service

The cable is used as a key component of the large infrastructures, such as stayed cablebridge, suspension bridge and Ferris wheel, and its health status affects the working life ofthese structures. It’s very important to test the cable for the safety of infrastructures. Themagnetic flux leakage (MFL) testing method and tool for in-service parallel wire cables arestudied in detailed in this thesis which is supported by National key Technology Research andDevelopment Program of China.Due to the complexity of structural characteristic of cables, MFL testing for cable ischaracterized by the large diameter and liftoff. Firstly, a MFL testing model is establishedusing the3D finite element method. The authentic signals of magnetic leakage field areobtained by subtracting the magnetic field signal of no defect from the defective field signals.The distribution of the MFL field is achieved, which are influenced by many parameters, suchas broken wire’s number, width, burial depth and liftoff, etc. And then, the curves are obtainedrepresenting distribution of the MFL field to above parameters. Finite element simulationprovides the basis for interpretation of MFL testing results and plays an important role inquantitative analysis of broken wires.Secondly, the influence of the geometric size of the magnetizer on cable magnetizationand signals of magnetic leakage field is analyzed through finite element method. Correlationcurves are given for the MFL signals along change in magnetizer size. Optimum dimension ofthe testing magnetizer is got through the ANSYS software. The number of the magnetizer isdiminished, at the same time the analysis results and the experimental results verify theconsistency of detection sensitivity in circumferential direction under the condition of threemagnetizers. The results can be used in magnetic circuit design for improving magnetic effectand testing signals, providing a method for optimizing the magnetization design and reducingthe volume and weight of the testing machine.At last, on the basis of the above theoretical research, the MFL testing tool is developed.Many kinds of measures are used to light the weight of crawl device. Its exercise performanceand detection performance are tested preliminarily. The experiment results show that thecrawl device can move smoothly and detect the flaw of one broken wire. The experimentresults also show that the MFL testing tool for cables have advantages of good stability andportability, which meets the need of field use and exhibits a bright application future.