1.The principle of the detection of oil-stolen orifice by permanent magnet disturbance 

Based on the magnetic disturbance phenomenon, permanent magnet disturbance detection is a newly-developing mode of non-destructive testing. After magnetizing the tested components, the space magnetic field maintains a steady state, in this case, the defects generate magnetic interaction forming a disturbance environment. Therefore, the defects can be inspected by detecting the instantaneous reconstruction of the internal magnetic field of the permanent magnet. 

Although the macro parameters, including the size and volume of the permanent magnet, caused by the magnetic disturbance experience unnoticeable changes, the internal magnetic field of the permanent magnet undergoes drastic changes. Therefore, such a method can be applied to measure the magnetic disturbance in a permanent magnet indirectly by using coils around the surface of the permanent magnet. The sensor structure is shown in Figure 1.  

Figure 1. The sensor structure of permanent magnetic disturbance

When the sensor of permanent magnetic disturbance scans the surface of the pipeline at a constant speed, it will generate magnetic interaction forming a magnetic disturbance environment. The pipeline will be magnetized by the permanent magnet, which gathers magnetic line of force inside the pipeline. If the pipeline has no defects, the magnetic line of force passing through the coils of the sensor should be equally distributed, without induced voltage. If oil-stolen orifice defects exist in the pipeline, the magnetic line of force will be refracted into the air with lower permeability, then the magnet field near the defects will grind against the original magnetic field of the permanent magnet, changing the original magnetic field with a steady state and causing a disturbance, which makes the magnetic line of force through the sensor uneven, generating induced voltage. By applying this structure, the permanent magnetic disturbance caused by the discontinuity of the defects of the pipeline will be inspected, so as to inspect oil-stolen orifice defects.

2.The signal features of the detection of oil-stolen orifice by permanent magnet disturbance

Figure 2. The detection signal of orifice defects

The peak value of the signal of the detection of the oil-stolen orifice by permanent magnet disturbance will increase gradually with the increase of aperture, and the signal experiences obvious mutation integrally compared with the defect-free position.

3.The structure of the detection system of oil-stolen orifice by permanent magnet disturbance  

The detection system is composed of a power cup, the primary probe, a processing module, and an odometer wheel. As shown in figure 3, the inspection part made up of the probe and processing module includes a signal processing circuit, gathering module, and storage system.

Figure 3. The detection system of oil-stolen orifice by permanent magnet disturbance