Corrosion non-destructive testing of loaded steel strand based on self-magnetic flux leakage effect

The metal magnetic memory is used to detect the micro damage of structure based on the SMFL (self-magnetic flux leakage) effect, but it lacks an effective comprehensive diagnosis index suitable for the ferromagnetic material. In this paper, steel strand specimens were tensioned at different force levels, and the experimental study on the corrosion detection was carried out. Besides the monitoring analysis of the cable force, the initial structural magnetic field ΔBx0 and the surface SMFL signals Bx(α) induced by corrosion were both analysed. The results show that ΔBx0 curves of steel strand material present the periodic fluctuation. Considering ΔBx0 and measuring distance z, the proposed dimensionless damage analysis index X can be used for the quantitative research of corrosion diagnosis. The small influence of the cable force on index X is also illustrated. Moreover, the strong correlation that exists between the average maximum index Xmax‾ and the corrosion ratio α is well fitted by the three-order polynomial curves.