Numerical Simulation and Experiment on Magnetic Flux Leakage Inspection of Cracks in Steels
The magnetic flux leakage inspection method is widely use d in the detection of pipelines, storage tanks and other steel materials. Especially in c orrosion pits detection, it has become a matured technology. As cracks may exist in the steels which may lead to big hazards, its detection becomes very important. Meanwhile, the cracks evaluation by MFL inspection can be determined by many parameters, it has much difficulty t o implement due to its weaker signals compared with pits. In this research, the finit e element model for cracks’ MFL is established and corresponding method are carried out. Furthe rmore, parameters such as depth, width, angle of cracks and scanning direction are analyzed. Also, the experiments are done which show great reliability comparing with numerical s imulations. The results show that the cracks can not be detected when the scanning direction para llels with it. So the cross-scanning method is recommended for MFL inspection on cracks.
A new optical technique for detection of defects in ferromagnetic materials and components
In this paper, we present the details of a new optical technique to detect the defects present in a ferromagnetic material or component, using a ferrofluid emulsion. This new flux leakage probe consists of monodispersed ferrofluid confined between two thin transparent glass slides or in a cuvette and a white light source for illumination. By employing ferrofluid droplets of suitable size and surfactant concentration, one can qualitatively identify the region where the defect is located in the test specimen by visually observing a color change in the ferrofluid cell, in the vicinity of a crack or defect in the test specimen. The origin of this color change in the back scattering direction is due to Bragg scattering from the droplet chains, formed by the leaked magnetic flux in the presence of a defect. We discuss in detail the procedure, the merits and potential uses of this new technique for non-destructive testing and evaluation (NDT and E) applications.
New findings in the field of non-destructive magnetic leakage field inspection
Abstract Non-destructive inspection of defects using the magnetic leakage flux method presents several experimental and theoritical difficulties. It is shown that the leakage field strength around a defect is linked linearly with the field strength inside it. Thus a prerequisite to a better understanding of the phenomenon is the determination of the magnetic field strength inside the defect as a function of defect geometry, magnetic properties of the material and applied field strength. Equations are presented which enable computation of this quantity. Discrepancies between measurement and calculations using the method of finite elements emphasize the need for accurate knowledge of the magnetic field strength inside the defect.