The Detection Probability Improvement of the Far-Side Crack on the High Lift-Off Using the Magnetic Camera

Abstract

To evaluate cracks using magnetic flux leakage (MFL), the distribution of magnetic field (DMF) near the crack should be quantified. A narrow spatial resolution of DMF is demanded around the crack. Also the lift-off should increase over several mm to protect the sensors from environments such as high temperature, dust, and vibration. Furthermore, the MFL must be amplified to detect a far-side crack because the MFL will concentrate in the ferromagnetic specimen and will be weak. The magnetic camera and magnetic lens could be useful for high lift-off conditions such as in nondestructive testing of a far-side environment. The far-side crack detection probabilities, Max(∂B/∂x) and RMS(∂B/∂x), were improved by about 20~60% by using the magnetic lens. The crack can be easily detected by using the 1/4RMS algorithm. Finally, an equation that expresses the relationship between the volume of crack and Max(∂B/∂x) is proposed. This equation is based on the principle that the magnetic field is inversely proportional to the square of the lift-off and is useful for determining the crack volume when the lift-off is known.

Comparison of Magneto-Optical Faraday Effect Method and Magnetic Camera for Imaging the 2-D Static Leakage Magnetic Flux Density

“…The process started from the power switching process to distinguish the responsible sensor lines in units of time. The captured electric signal is concentrated using a magnetic lens to increase signal intensity [10], [47]. However, the recent development of semiconductor technologies improves the signal amplification without a magnetic lens using a differential-type operational amplifier (OP-AMP), making the process more independent.…”

A Method for Improving SNR of Drill Pipe Leakage Flux Testing Signals by Means of Magnetic Concentrating Effect

“…Very little work has been reported on wellhead online testing technique. Some related publications about the ability of MFL machines to reduce the requirements of liftoff value are found using the magnetic camera [4], [5], a very closely related application, but is not suitable for the severe condition of rig wellhead part. This paper analyses the reason why SNR of MFL signals is quite low by the integration of theory and experiment, and optimizes the structure of MFL sensor using magnetic concentrating principle, thus reduce the requirements of liftoff value and improves the precision of MFL testing.…”

Magnetic camera for visualizing magnetic fields of home appliances

“…The system can detect smallest cracks of a hole-type with 0.25 mm radius and 1.0 mm depth. Lee and Hwang, et al [17], [18] also applied different methods to improve the detection probability of the far-side crack by using 1/4 RMS algorithm and inspected specimen at high temperature using a high spatial resolution magnetic camera. Jun,et al [19] proposed a hand-held magnetic camera system for inspecting crack on aluminium alloy.…”