Analysis of Large Diameter Seamless Steel Tube Flaw Detection

The large-diameter seamless steel tube is characterized by a large diameter and a relatively thick wall thickness. Therefore, according to this feature, the combination of ultrasonic detection inside and the characteristics of the eddy current detecting surface and the sub-surface can be used to realize the "no blind zone" flaw detection. By adopting the "combination method of in-situ rotation of the steel pipe and detecting the advancement of the probe", not only the detection problem is solved, but also the space for occupying the occupied space is solved.

In the field of flaw detection technology, large-diameter seamless steel tube refer to steel pipes with an outer diameter greater than?160 mm. Large diameter seamless steel tube is an important material for petroleum, chemical, heat, boiler, mechanical hydraulic and other industries. Following the development of the national economy, during the "Eleventh Five-Year Plan" period, the demand for seamless steel tubes in China increased significantly, and it showed a large-caliber development trend. Especially for oil well pipes and large-diameter high-pressure boiler pipes that require corrosion resistance and anti-extrusion, high-quality oil cracking pipes, petroleum and petrochemical pipelines, etc., will be followed by the country’s increased investment in energy-based initiatives. Popular. Therefore, the non-destructive testing of the quality of the products is proposed to propose new methods and techniques. Therefore, for the detection of large-diameter steel pipes at home and abroad, magnetic flux leakage or water pressure experiments are generally used. In the sea, there is no magnetic leakage testing equipment suitable for large-diameter steel pipes, which is well-functioning. Inlet magnetic flux leakage testing equipment is expensive and difficult for most companies in the country to accept; the water pressure test is inefficient and labor intensive, especially when the operator's responsibility is not high, the water pressure maintenance is ineffective. It can be seen that the detection of large-diameter seamless steel tubes has become an urgent problem to be solved in the metallurgical steel pipe industry. The eddy current through the coil is detected by a circumferential surface of the surface of the steel pipe. In the eddy current flaw detection using the through coil, the larger the diameter of the detected steel pipe, the larger the circumferential area detected by the coil, and the lower the signal to noise ratio. For this reason, the eddy current flaw detection scale of steel pipe is delineated, and the eddy current flaw detection of the through coil is adopted, and the outer diameter of the steel pipe is not more than 140 mm. In addition, in the case of large-diameter steel pipe through-type flaw detection, the magnetization and demagnetization of the steel pipe have certain difficulties. The sink type ultrasonic inspection adopts a steel pipe spiral advance type, and the ultrasonic probe is fixed. The thickness of the coupling layer is ensured by the characteristics of sufficient water coupling between the water tank and the bottom of the steel pipe to be inspected. However, since the ultrasonic mainly detects the internal defects, there is a blind zone on the surface and the subsurface defects, which makes it impossible to detect. In addition, the use of the spiral advance type requires a space of 30 m for a 12 m long seamless pipe, which has always affected the detection method of the steel pipe. Choice and promotion.

At present, the detection of seamless steel tubes for high-pressure boilers in China's metallurgical industry is mainly applied to the specifications below?160mm, and most of them adopt the traditional eddy current testing or independent sink ultrasonic testing methods. For the seamless steel tube exceeding?160mm, the traditional through-flow eddy current method is used for testing, and there are many problems, which are not accepted by the national scale. If independent ultrasonic testing is used, the ultrasonic testing mechanism has a blind spot with a certain depth on the surface, which cannot guarantee the reliability of the overall test results of the steel pipe.

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