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The Metal Magnetic Memory Testing technology is a completely new method in recent years. The reassigned wavelet scalogram analysis method can improve the aggregation of scalogram, reduce interference terms, and be understood easily to some extent. Aiming at the deficiency of using Metal Magnetic Memory Testing to recognise pipeline defect, the reassigned wavelet scalogram analysis method is put forward to analysis the Metal Magnetic Memory Testing signal in this paper. The experimental research proves that the reassigned wavelet scalogram effectively used for Pipeline Defect Recognition by Metal Magnetic Memory Testing. Introduction In the traditional five mode of transportation, pipeline transportation has a unique advantage. It has large capacity, less land occupation, short construction period, low cost and less energy consumption. After many years of oil and gas pipeline operation, there will inevitably be various defects, such as corrosion layer damage, metal corrosion, external force damage and so on. In 1990s, the Russian scholar Doubov took the lead in putting forward a new nondestructive testing technology, metal magnetic memory detection technology, called magnetic memory testing. As shown in Figure 1, the basic principle of the Metal Magnetic Memory Testing technology can be expressed as: For the effect of the load, the domain organization orientation will cause magnetostriction properties and irreversible reorientation in the Ferromagnetic components working in a geomagnetic field. The maximum leakage magnetic field is formed in the stress and deformation zone. The tangential component of the magnetic field in the stress concentration area ( ) P H x has the maximum value, while the sign of the normal component ( ) P H y changes and has zero-crossing position. The irreversible change of the magnetic state remains after the elimination of the working load. By the testing of the magnetic flux leakage field’s normal component ) (y H P and the calculation of gradient, the stress concentration position of the component can be exactly deduced[1,2,3].thus, the defects such as the micro crack developed from the stress concentration can be detected. Figure 1. Schematic of magnetic memory method.

A Judgment Criteria and Its Application for Magnetic Memory Testing Based on the Reassigned Wavelet Scalogram