Yihua Kang

Magnetic mechanisms of magnetic flux leakage nondestructive testing

The widely applied magnetic flux leakage (MFL) nondestructive testing for ferrous materials has been simply explained by “MFL escaping from defects and being induced is exactly the MFL testing principle,” with a rough application for evaluation. Hence, we analyze the “escape” course of MFL generation using magnetic refraction and explain the reason why the MFL technology really exists in practice. Furthermore, we also point out that the presently so-called MFL testing technique essentially hides a different signal component arising from bump-shaped defects features unlike the MFL caused by concave-shaped ones, explained by another forming mechanism.

Theoretical Analyses of MFL Signal Affected by Discontinuity Orientation and Sensor-Scanning Direction

To improve the accuracy of the magnetic flux leakage (MFL) nondestructive testing in practical applications, we analyzed the MFL signal characteristics affected by discontinuity orientation and sensor-scanning direction. On the basis of magnetic dipole theory, the descriptions for the MFL field distributions of discontinuities in arbitrary orientations were established, indicating that the MFL density increases with the discontinuity orientation increasing from 0 to

Research on reconfigurable robot technology for cable maintenance of cable-stayed bridges in-service

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An Opening Electric-MFL Detector for the NDT of In-Service Mine Hoist Wire

/2 and that magnetic flux always flows through the discontinuity perpendicularly, which was verified by relevant experiments. Further, the influence of the sensor-scanning direction on MFL signal features was analyzed and it was found that the MFL component signal parallel to scanning direction increases, the MFL component signal perpendicular to scanning direction falls, the MFL component signal perpendicular to discontinuity stays the same, and the widths of test signals become narrow, when the angle between the discontinuity orientation and sensor-scanning direction increases.

A new magnetic flux leakage sensor based on open magnetizing method and its on-line automated structural health monitoring methodology:

In this paper, according to the technical characteristics of the maintenance of cable of cable-stayed bridges, a new robot for cable maintenance is developed. The climbing equipment, the surface inspection equipment and the internal defects inspection equipment, the cleaning equipment, the spraying equipment for cable maintenance are all designed as reconfigurable module. According to different cable diameters, different numbers of robot modules are reconstructed to form corresponding maintenance robot. The magnetic mechanisms that are used in the climbing equipment of robot keep the robot cling to the cable. The robot can climb cable along by wheels which installed on it. The robot has many advantages, such as simple structure, easy manipulative, fast moving, the less damage to the cable and the good adaptability to the shape of the cable.

Development of an inspection robot for long‐distance transmission pipeline on‐site overhaul

There has not been an electric-magnetic flux leakage (MFL) detector enabling nondestructively testing the in-service mine hoist wire ropes fixed at both ends mainly due to the tubular configuration of solenoids as electric magnetizers. Hence, an opening electric magnetizer is proposed based on the magnetic control for a C-like electric loop-coil, featured by an opening structure capable of directly encompassing and centering the endless object in it. Subsequently, the magnetization effect similar to the conventional solenoids is confirmed by simulations and experiments with the designed 3-D models and prototypes. Finally, an opening electric-MFL detector chiefly consisting of the opening electric magnetizer is presented, capable of directly encircling the endless ropes, and meanwhile two application cases of the relevant apparatuses for the in-service mine hoist wire ropes are given with a good detection effect. The emergence of the opening electric magnetizer and its detector can expand the application ranges beyond of the traditional tubular solenoids and their corresponding tubular sensors, including other electromagnetic excitation or nondestructive testing for the endless objects, such as railway and coiled tubing in service.

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

Magnetic flux leakage sensors have been widely used for the structural health monitoring of ferrous materials (structural health monitoring). This article provides a new magnetic flux leakage sensor based on open magnetizing method. Starting with the traditional yoke magnetization method analyses, the provided open magnetizing method and testing principle are presented. Then, the comparative analyses between the two methods are conducted by finite element method, indicating that the open magnetizing method features less magnetic interaction force, more uniform magnetic flux density for swing scanning, simpler architectures, and more universal functions under the framework of similar magnetic excitation capability for defects. Furthermore, the sensor based on open magnetizing method is designed through optimization and the advantages for open magnetization method are confirmed by experiments with created sensors. Finally, on-line structural health monitoring methodology for the monitoring probe with “rigid” open–close and “free” tracking rope-swing functions is developed based on the proposed sensors. Meanwhile, experimental comparisons between the open and yoke probes for on-line automated monitoring are also conducted to successfully confirm the characters of smaller magnetic interaction force, less wear, and damage in contrast to the traditional on-line automated structural health monitoring technology. Additionally, the on-line automated magnetic flux leakage apparatus for the structural health monitoring of hoist wire ropes is developed and applied, which further confirms the good practicability for the structural health monitoring of hoist ropes under the poor working conditions.

The Effect of Motion-Induced Eddy Current on Circumferential Magnetization in MFL Testing for a Steel Pipe

Purpose – Damage of oil and gas long‐distance transmission pipelines caused by corrosion, stresses, geological change, and other factors can result in catastrophic failures. The purpose of this paper is to describe a mobile out‐pipe inspection robot for the pipeline inspection.Design/methodology/approach – This paper adapts to the requirements of long‐distance transmission pipelines on‐site overhaul, the robot developed in this paper utilizes a local magnetic flux leakage testing method for the pipeline inspection. Detection, walking, attachment, steering, and control units are designed for the robot.Findings – The detection apparatus of the robot plays dual roles as detection and attachment unit. So, the structure of the robot is relatively simple and it is relatively small in size and relatively light.Practical implications – A prototype of the robot has been manufactured according to the design. Results of the test in lab show the robot can be used to inspect pipe.Originality/value – The robot is able ...

Theoretical Analysis and Numerical Simulation of the Feasibility of Inspecting Nonferromagnetic Conductors by an MFL Testing Apparatus

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.

Broken wire detection in stay cables based on guided waves

Eddy current effect essentially occurs when a relative movement happens between steel pipes and the circumferential magnetizer in high-speed magnetic flux leakage (MFL) testing. To improve the MFL testing for longitudinal defects, the effect of motion-induced eddy current (MIEC) on circumferential magnetization is analyzed. First, in terms of Maxwell equations, the eddy current effect and the MIEC distribution in the steel pipe are analyzed. Then, the finite-element simulations are conducted to investigate the MIEC distribution, the magnetization status change, and the sensitivity difference. With the rotational speed increasing, the MIEC and circumferential magnetic flux density gradually become asymmetrical and non-uniform. The MFL testing signal amplitudes of external and internal defects in the arriving and leaving parts change in different variation trends. Finally, the relevant high-speed MFL testing experiments for steel pipes are performed to confirm the effect of MIEC. The experimental results match well with the theoretical analysis and numerical simulation results.