AC and DC composite magnetisation based leakage detection recognition method for inside and outside wall defect

Abstract

A method for recognizing defects on inner and outer walls by magnetic flux leakage detection based on AC/DC combined magnetization is used for determining whether a defect is present on inner or outer wall of a material to be detected, which belongs to nondestructive detection field. The method is characterized in that the method comprises three basic steps of: (1) subjecting the material to magnetic flux leakage detection by AC/DC combined magnetization; (2) subjecting the magnetic flux leakage signals detected by a sensor to spectral analysis to obtain the magnitude of the frequency component of an AC magnetic flux leakage signal of a defect portion; and (3) setting the threshold of an AC frequency component and comparing the AC frequency component of the magnetic flux leakage signal with the threshold to determine whether the defect is present on the inner wall or on the outer wall of the material. The invention can conveniently determine the defect position and simultaneously execute inner/outer wall recognition by one-step magnetic flux leakage detection, thus facilitating the development of defect quantization after magnetic flux leakage detection.

Description

technical field [0001] The invention relates to a magnetic flux leakage detection method of alternating and direct current composite magnetization, which is used for identifying inner and outer walls of defects, and belongs to the technical field of nondestructive testing. Background technique [0002] Magnetic flux leakage testing is a more commonly used non-destructive testing method, which is widely used in ferromagnetic material quality testing and safety monitoring. However, it is always non-destructive to identify defects on the inner and outer walls of the tested material and distinguish whether the defect is on the inner wall or the outer wall of the tested material. A technical problem in the field of detection research. Chinese patent literature discloses a "method for identifying types of corrosion defects in pipelines" (publication number: CN1587785, publication date: 2005.3.2), which involves a technique for distinguishing corrosion defects in pipelines, such as...

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Problems solved by technology

Chinese patent literature discloses a "method for identifying types of corrosion defects in pipelines" (publication number: CN1587785, publication date: 2005.3.2), which involves a technique for distinguishing corrosion defects in pipelines, such as "general corrosion defects", "corrosion pit defect", "axial groove", "circumferential groove", "pinhole defect", "axial groove defect", "circumferential groove defect", etc., but this technology cannot be used to distinguish the inner and outer wall characteristics of defects

However, this technology can only locate the defect in the direction of the length of the pipeline, and it is still unable to determine the information of the inner and outer walls of the defect

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