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

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 be fully covered with automatic wall thickness testing. 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 information of the magnetic field change 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 a coupling agent, but it is difficult to excite ultrasonic waves in pipes with uneven surfaces. Industrial ultrasonic phased array probes are expensive to manufacture and complex in systems. At present, such equipment is rarely seen 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 detection of oil casing and selected the appropriate focal length and chip size probe to form a full-coverage automatic wall-thickness detection system. Significant improvement has been made. The design and selection of the probe are crucial to the thickness of the oil casing. Generally, the sound beam emitted by the circular crystal plate of the probe has a certain diameter and expands with the increase of the distance. The selected sound beam is focused locally through the acoustic lens. to boost energy.

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