PIPELINE INSPECTION

1.The principle of oil-stolen orifice detection technology via permanent magnet disturbance

As a newly-developing mode of non-destructive testing, permanent magnet disturbance detection is based on the magnetic disturbance phenomenon. Once a testing component is magnetized, its space magnetic field maintains a steady state, however, a defect would give rise to magnetic interaction causing a disturbance environment. Therefore, the defect can be inspected by detecting the instantaneous reconstruction of the internal magnetic field of the permanent magnet.

The magnetic disturbance has little influence on the size and volume of the permanent magnet, but the internal magnetic field of the permanent magnet go through drastic changes. Therefore, the magnetic disturbance can only be measured indirectly by using coils around the surface of the permanent magnet. The sensor structure is shown in Figure 1.

When the permanent magnetic disturbance sensor scans the pipeline surface at a constant speed, magnetic interaction occurs forming a magnetic disturbance environment. The pipeline then is 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 the pipeline has oil-stolen orifice defects, the magnetic line of force will be refracted into the air with lower permeability, at the moment the magnet field near the defects will grind against the original magnetic field of the permanent magnet, changing the original steady-state magnetic field and causing a disturbance, which makes the magnetic line of force through the sensor uneven, generating induced voltage. Therefore, this structure can be used to detect permanent magnetic disturbance caused by the discontinuity of pipeline defects, so as to achieve oil-stolen orifice detection.

2.The signal features of oil-stolen orifice detection technology

When using the oil-stolen orifice detection technology via permanent magnet disturbance, the detection signal peak will increase gradually as the aperture increases, and the signal experiences abrupt changes integrally compared with defect-free position.

3.The system structure of oil-stolen orifice detection technology

The detection system is composed of power cups, primary probes, the main processing module, and odometer wheels. As shown in figure 3, the detection section made up of probes and the main processing module includes a signal processing circuit, gathering module and storage system.