First, what is the significance of the heat treatment process for oil casing?
Besides its use in oil extraction, oil casing also serves as a pipeline for transporting raw materials. To enhance the quality of oil casing, every step of the production process is crucial, especially temperature control, which must be strictly adhered to. Typically, oil casing uses sub-critical quenching instead of conventional quenching. Conventional quenching leaves residual stress inside the workpiece, increasing brittleness and making subsequent processing more difficult. Sub-critical quenching prevents excessive brittleness from affecting subsequent processes. The main operating method is to first select the sub-critical quenching heating temperature, usually between 740-810℃, for approximately 15 minutes. After quenching, tempering is performed for 50 minutes at 630℃. Of course, different types of steel have their own specific heating temperatures and times for heat treatment; as long as the performance of the workpiece is improved, the purpose of heat treatment is achieved.
Heat treatment is the most crucial process in oil casing manufacturing. The performance and quality of the finished product largely depend on the heat treatment results. Therefore, manufacturers maintain extremely strict requirements for the heat treatment process, leaving no room for negligence. Sometimes, low-temperature quenching is used. Low-temperature quenching effectively removes residual stress from the oil casing, reducing post-quenching deformation and shaping the casing into a more suitable raw material for subsequent processes. Thus, the current achievements in oil casing are inseparable from heat treatment. Since the introduction of this processing step, the impact toughness, damage resistance, and tensile strength of oil casing have all significantly improved.
Secondly, what factors affect the accuracy and resolution of oil casing wall thickness measurement?
API standards stipulate that the inner and outer surfaces of inlet and outlet oil casings must be free of folds, separations, cracks, and scratches. These defects must be thoroughly removed to a depth not less than 12.5% of the nominal wall thickness. Oil casings must undergo full-coverage automatic wall thickness measurement. Currently, there is an indirect wall thickness measurement method based on the principle of magnetic leakage. It’s not a direct method of measuring wall thickness, but rather an indirect method that measures wall thickness indirectly by measuring the changes in the magnetic field caused by variations in wall thickness.
Therefore, the magnetic field strength has a significant impact on the accuracy and resolution of wall thickness detection, making it unsuitable for online automated inspection. Magnetosonic testing does not require coupling agents, but it’s difficult to excite ultrasonic waves in pipes with uneven surfaces. Industrial ultrasonic phased array probes are expensive to manufacture, and the systems are complex. Currently, such equipment is rare in my country.
Based on the principle of ultrasonic measurement of oil casing wall thickness, oil casing manufacturers analyzed focusing probes suitable for automated oil casing inspection. By selecting probes with appropriate focal lengths and crystal sizes, a full-coverage automated wall thickness detection system was constructed, resulting in significant improvements within the full coverage range. The design and selection of the probe are crucial to the thickness of the oil casing. Generally, the acoustic beam emitted by the circular crystal of the probe has a certain diameter and expands with increasing distance. Selecting an acoustic beam and focusing it locally through an acoustic lens increases energy.
After the oil casing inspection is completed, a thickness detector is installed to fully cover the area. The ultrasonic thickness detection system is generally tested afterward, using equipment such as a magnetic flux leakage detection system. Under the given parameters, adjust the probe angle to determine the rotational speed of the rotary motor and the scanning speed of the oil casing.
Post time: Mar-09-2026