Online nondestructive testing for fine steel wire rope in electromagnetic interference environment

The diameter of fine steel wire rope (FSWR) is generally a few millimeters. Its magnetic flux leakage (MFL) signal is weak, and the number of magnetic sensors installed for defect detection is limited because of the small diameter. In FSWR production workshops, different kinds of machinery work together, deteriorating the power quality and making the spatial electromagnetic environment complex; the weak MFL is thus interfered with further. It is difficult to carry out online nondestructive testing (NDT) of FSWR in the process of manufacturing. In this paper we present a novel MFL method for FSWR NDT in a strong electromagnetic interference environment. We use a three-dimensional finite element method (FEM) to analyze the MFL signals. A simplified magnetic circuit is presented to excite the FSWR; the circuit comprises two half-sized radial magnetizing ring NdFeB magnets, and because there is no need for a magnetic yoke, the device is simple and light. A single Hall sensor is used to measure the flux leakage field. A stable performance power system is designed for the NDT power supply, which is not only resistant to voltage sags, but also has very low output noise. To enhance the signal-to-noise ratio (SNR) of the MFL defects signal, a signal conditioning and processing circuit are designed to enhance the detectability of signals in MFL data. The novel and small FSWR NDT system realizes on-line testing in an environment of strong electromagnetic interference, and for the experiment with a 1.5-mm-diameter wire rope twisted by 19 wires, the minimum damage of a pit on half of a wire can be identified.