Factors affecting the accuracy and resolution of oil casing wall thickness testing, including heat treatment and inspection

First, heat treatment of oil casing. 
Besides oil extraction, oil casing also serves as a pipeline for transporting raw materials. To ensure 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 hindering subsequent processing. Sub-critical quenching prevents excessive brittleness from affecting subsequent processes. The main procedure involves selecting a sub-critical quenching temperature, typically between 740-810℃, for about 15 minutes. After quenching, tempering is performed for 50 minutes at 630℃. Of course, different steels 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 step in the processing of oil casing. The performance and quality of the finished product largely depend on the results of heat treatment. Therefore, manufacturers have extremely strict requirements for the heat treatment process and dare not be negligent in the slightest. Sometimes, low-temperature quenching can be used. Low-temperature quenching effectively removes residual stress from the oil casing, reducing the degree of deformation after quenching and making the oil casing a more suitable raw material for subsequent processes. Therefore, 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 been greatly improved.

Secondly, factors affecting the accuracy and resolution of oil casing wall thickness detection.
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 should be completely removed, with a removal depth not less than 12.5% of the nominal wall thickness. Oil casings must undergo full-coverage automatic wall thickness detection. Currently, there is an indirect method for measuring the wall thickness of oil casings based on the principle of magnetic leakage. It's not a method of directly measuring the wall thickness of oil casing, but rather an indirect method that measures the wall thickness indirectly by measuring the magnetic field changes caused by variations in the wall thickness. Therefore, the magnetic field strength has a significant impact on the accuracy and resolution of oil casing wall thickness detection, making it unsuitable for online automated inspection. Magnetosonic testing 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. 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 automatic oil casing inspection, selecting appropriate focal lengths and crystal sizes to construct a full-coverage automatic wall thickness detection system, 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 after other equipment (e.g., magnetic flux leakage detection systems). 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.