Factors Affecting the Accuracy and Resolution of Wall Thickness Detection of Oil Casing

The API standard stipulates that the inner and outer surfaces of the import and export oil casing shall not have folds, separations, cracks, and scars. These defects should be completely removed, and the removal depth should not be less than 12.5% of the nominal wall thickness. Oil casing must undergo full coverage automatic wall thickness detection. At present, there is an indirect measurement method of wall thickness based on the principle of magnetic flux leakage. It is not a method of directly measuring the wall thickness, but a method of indirectly measuring the wall thickness by measuring the magnetic field change information caused by the change of the wall thickness.

Therefore, the magnetic field strength has a great influence on the accuracy and resolution of wall thickness detection, which is not suitable for online automatic detection. Magnetic ultrasound does not require coupling agents, but it is difficult to excite ultrasound in pipes with uneven surfaces. Industrial ultrasonic phased array probes have high manufacturing costs and complex systems. At present, this kind of equipment rarely appears in our country.

According to the principle of ultrasonic measurement of oil casing wall thickness, the oil casing manufacturer analyzed the focusing probe suitable for automatic inspection of oil casing, and selected the appropriate focal length and wafer size probe to form a full-coverage automatic wall thickness detection system. marked improvement. The design and selection of the probe are very important to the thickness of the oil casing. Generally, the acoustic beam emitted by the circular crystal plate of the probe has a certain diameter and expands with the increase of the distance. The acoustic beam is selected to be locally focused through the acoustic lens. to increase energy.

After the oil casing inspection is completed, the required thickness detector is completely covered, and the ultrasonic thickness detection system is generally installed after the test equipment (for example, the magnetic flux leakage detection system). Under the conditions of the parameters, adjust the angle of the probe to determine the rotational speed of the rotating motor and the scanning speed of the oil casing.