Magnetic flux leakage structural health monitoring of concrete rebar using an open electromagnetic excitation technique

Abstract

The current methods of electric–magnetic flux leakage structural health monitoring that use tubular coils as electro-magnetizers fail to detect concrete rebar structures without a head and a tail. This article proposes a novel electric–magnetic flux leakage structural health monitoring technique for concrete rebar using open electromagnetic coils as magnetizers. Three-dimensional finite element simulations and experiments are conducted to compare the magnetization effect, defect-detection capability, and magnetic force interaction of traditional tubular coils and the proposed open electromagnetic coils. The agreement between the simulation and experimental results confirms the reliability and validity of the proposed structural health monitoring technique for concrete rebar. Additionally, two types of magnetizer coils are designed and manufactured using optimized structures, and both limitations and solutions are discussed. Overall, the proposed open magnetizer coils show great potential for future structural health monitoring applications for concrete rebar.

Design and Optimization of an MFL Coil Sensor Apparatus Based on Numerical Survey

“…Magnetic flux can be generated by either a permanent magnet or solenoid. Also, according to the principles of the MFL method, a specimen must be saturated [2,8,23]. To provide a strong magnetic field for magnetizing a specimen, both the number of coil turns and the amplitude of the current (either AC or DC) must be large enough.…”

“…Therefore, it was decided to identify the optimum length for the permanent magnets. In order to achieve this goal, seven different lengths with a constant distance to the center of the yoke were considered and simulated, while the magnitude of the magnetic flux density was assumed strong enough to saturate the specimen completely (according to the principal of the MFL method) [2,8,23] and all other parameters were considered to have constant values. These seven values were 2, 4, 6, 8, 10, 12, and 14 cm.…”

“…Hence, demand for SHM using non-destructive testing (NDT) methods has increased significantly. Currently, there are a variety of conventional methods which are being applied based on non-destructive SHM principles such as visual inspection [6], magnetic flux leakage (MFL) [7,8], eddy current sensing [9,10], acoustic emission [11,12,13,14,15], and guided wave [16,17,18], among other techniques.…”

A Lift-Off-Tolerant Magnetic Flux Leakage Testing Method for Drill Pipes at Wellhead

“…Therefore, to avoid accidents and economic losses, according to the API (American Petroleum Institute) standard, drill pipes should be inspected by NDT (nondestructive testing) technologies before use [ 2 ]. MFL (magnetic flux leakage) technology is one of the most commonly used and powerful NDT methods and has been applied for the highly efficient inspection of defects in various kinds of ferromagnetic materials [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], particularly in elongated ferromagnetic objects, such as steel pipes [ 12 , 13 , 14 , 15 , 16 , 17 ] and wire ropes [ 18 , 19 , 20 , 21 ]. There are three types of MFL methods, namely, DC MFL, AC MFL, and pulsed MFL [ 22 , 23 ].…”

A New Method of SHM for Steel Wire Rope and its Apparatus

“…The magnetic fields inside the electrical arc are too weak to use for saturation magnetizing of the tested objects, which mainly arises from the offset of the "positive" and "negative" magnetic fields separately produced by the "forward" current (I) and "backward" current (I'), as shown in Figure 1(c) [11]. As a consequence, a ferrous core is arranged between the forward current (I) and the backward current (I'), as shown in Figure 1(d); this core is designed to increase the "positive" magnetic fields (H) of the forward current using the magnetic-gathering effect.…”