Nondestructive Testing of Steel Corrosion in Prestressed Concrete Structures using the Magnetic Flux Leakage System

Abstract

The Magnetic Flux Leakage (MFL) method can be nondestructively used to disclose the location and extent of corrosion or fracture in prestressed strands in concrete structures. In this study, parameters with the greatest effect on the performance of the MFL system are investigated using numerical simulations. The MFL system under study is based on two permanent magnets to magnetize embedded strands and Hall-effect sensors to detect normal magnetic flux leakage. The system is assessed using magnetostatic and transient numerical analysis to effectively simulate the MFL system. Results have been verified by laboratory and field experiments. Both normal and axial Hall-effect sensors are modeled in simulations to better identify magnetic signals at the corrosion zone. The sensor lift-off and the magnetic field masking by lateral reinforcements on nearby pitting corrosion are addressed as two main drawbacks of using MFL systems to detect corrosion in prestressed concrete structures. To provide more details about the flux leakage interference between the pitting corrosion and lateral reinforcements in prestressed concrete structures, linear and oriented magnets/sensor arrays are proposed and analyzed numerically.