Magnetic Flux Leakage-based steel cable NDE and damage visualization on a cable climbing robot

The steel cables in long span bridges such as cable-stayed bridges and suspension bridges are critical members which suspend the load of main girders and bridge floor slabs. Damage of cable members can occur in the form of crosssectional loss caused by fatigue, wear, and fracture, which can lead to structural failure due to concentrated stress in the cable. Therefore, nondestructive examination of steel cables is necessary so that the cross-sectional loss can be detected. Thus, an automated cable monitoring system using a suitable NDE technique and a cable climbing robot is proposed. In this study, an MFL (Magnetic Flux Leakage- based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults (LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the level of damage. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. In addition, the measured magnetic flux signal was visualized into a 3D MFL map for convenient cable monitoring. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.