Purpose of Carbon Steel Seamless Pipe Flaw Detection

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 pipe exceeding?160mm, the traditional through-flow eddy current method is used for testing, and there are many problems, which are not allowed by national standards. If independent ultrasonic testing is used, the ultrasonic detection mechanism has a blind spot with a certain depth on the surface, and the reliability of the overall test result of the steel pipe cannot be guaranteed.

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. It is for this reason that the standard for eddy current testing of steel pipes stipulates that the eddy current flaw detection of the through-coil must not exceed 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, because the ultrasonic mainly detects the internal defects and the blind areas of the surface and subsurface defects, which makes it impossible to detect, and the use of the spiral advance type, the space of the 12 m long steel pipe needs to occupy a space of 30 m, which has always affected the selection of the steel pipe detection method and Promotion.

Therefore, at home and abroad, for the detection of large-diameter steel pipes, magnetic flux leakage or water pressure experiments are generally used. In China, there is no good performance of magnetic flux leakage testing equipment suitable for large diameter steel pipes. Once used, it needs to be imported. Imported magnetic flux leakage testing equipment is expensive, and it is difficult for most domestic enterprises to accept; and the hydraulic pressure test has low efficiency and high labor intensity, especially when the operator's responsibility is not high, the water pressure test is ineffective. It can be seen that the detection of large-diameter seamless steel pipes has become an urgent problem to be solved in the metallurgical steel pipe industry.

The large-diameter steel pipe 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.

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