Permanent magnetic and alternating current direct current composite magnetic flux leakage detecting method

Abstract

A permanent magnetic and alternating current direct current composite magnetic flux leakage detecting method relates to a magnetic flux leakage detecting method of a pipeline. A magnetizer is composed of a U-shaped magnetic core and a permanent magnet, and an exciting coil is wound around the U-shaped magnetic core. By giving different excitation to the exciting coil, the exciting coil and the permanent magnetic generate composite direct current magnetic field and alternating magnetization field in time-sharing mode. During measurement, the direct current magnetic field magnetizes a ferromagnet to be detected to a deep saturation state, a detected leakage magnetic field signal B1 is compared with a set threshold lambda 1, and whether defects exist in the ferromagnet to be detected is judged; if the defects exist, the alternating magnetization field magnetizes a component to be detected, and an alternating current frequency component B2 of leakage magnetic field strength is compared with a set threshold lambda 2 so as to judge if the defects exist on the inner surface or the outer surface. The method effectively overcomes the defects in the prior art that the defects of the inner surface and the outer surface can not be identified efficiently and accurately and has the advantages of being simple in principle, convenient to operate, free of coupling agent, non-contact in measurement and the like.

Description

technical field [0001] The invention relates to a magnetic flux leakage detection method for pipelines, in particular to a magnetic flux leakage detection method combined with permanent magnets and alternating current and direct current. Background technique [0002] The current pipeline testing methods generally include magnetic flux leakage testing, ultrasonic testing, far-field eddy current testing, and ray testing. Among them, magnetic flux leakage testing is one of the most commonly used methods in the field of non-destructive testing. It is suitable for the detection of surface and internal defects of various ferromagnetic material components (such as rails, steel pipes, steel wire ropes, tanks, etc.), so it has been deeply studied. development and wide application. However, on the issue of magnetic flux leakage detection for distinguishing inner and outer surface defects, researches at home and abroad are relatively rare. Domestically imported equipment is mainly im...

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Problems solved by technology

However, this method requires secondary processing on the detected leakage magnetic field signal to obtain the leakage magnetic field data of the DC and AC components, which reduces the signal-to-noise ratio and increases the detection complexity and measurement error

At the same time, in order to generate a sufficiently large magnetization field, its magnetizer is often large and requires a large excitation signal

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