In the field of large-diameter seamless steel pipe inspection technology, large-diameter seamless steel pipe is a steel pipe whose outer diameter is larger than φ160mm. It is an important material for petroleum, chemical, thermal, boiler, mechanical hydraulics and other industries. With the development of the national economy, during the “11th Five-Year Plan” period, China’s demand for seamless steel pipe and erw steel pipe increased significantly, and it clearly showed a trend of development with a large diameter. In particular, oil well pipes and large-diameter high-pressure boiler tubes, high-quality oil cracking pipes, and petroleum and petrochemical transmission line pipes, which require corrosion resistance and extrusion resistance, will become demanded as the country’s investment in energy infrastructure increases. Hot spot. As a result, non-destructive testing to ensure product quality at the factory presents new methods and technical issues.
At present, the detection of high-pressure boiler seamless steel tubes in the metallurgical industry is mainly focused on the following φ160mm specifications, and most of them adopt traditional eddy current testing or independent sink-type ultrasonic testing methods for passing-through coils. For the seamless steel tubes over φ160mm, the traditional through-flow eddy current method is used for testing, and there are many problems that are not allowed by national standards. If independent ultrasonic testing is used, there is a blind spot on the surface of the surface due to the ultrasonic testing mechanism, which does not guarantee the reliability of the overall steel pipe test results.
The eddy current through the coil is a circumferential surface of the steel tube. In eddy current flaw detection using a through-type coil, the larger the diameter of the detected steel pipe, the greater the circle area detected by the coil and the lower the signal-to-noise ratio. It is for this reason that the eddy current flaw detection standard for steel tubes stipulates that the eddy current flaw detection of the through-type coils should not exceed the size of 140 mm. In addition, it has certain difficulty in the magnetization and demagnetization of the steel pipe during the through-type inspection.
Sink-type ultrasonic testing uses spiral steel pipe advancement, and the ultrasonic probe is fixed. Through the full water coupling characteristics of the bottom of the water tank and the tested steel pipe, the thickness of the coupling layer is not changed. However, due to the detection of internal flaws in the main defects of the surface and subsurface flaws caused by ultrasound, can not be detected, coupled with the use of spiral advancing type, for the 12m long steel pipe space needs 30m space and other deficiencies, has always affected the choice of steel pipe testing methods and Promotion.
Therefore, at home and abroad for the detection of large-diameter steel pipe, leakage magnetic method or water pressure test is generally used. In China, there are no well-performing magnetic flux leakage testing equipment suitable for large-diameter steel pipes and they need to be imported once they are used. Imported magnetic flux leakage testing equipment is expensive and difficult to accept for most domestic enterprises. The hydrostatic test is inefficient and labor-intensive, especially when the operator’s sense of responsibility is not high. The water pressure test is void. It can be seen that the detection of large-caliber seamless steel tubes has become a pressing issue for the metallurgical steel pipe industry.
Large-diameter steel pipe is characterized by its large diameter and relatively thick wall thickness. Therefore, according to this feature, the combination of ultrasonic detection inside and eddy current detection surface and sub-surface features can be combined to achieve “no blind spot” inspection. By adopting the “combination method in which the steel pipe rotates in place and detects the advancement of the probe”, not only the detection problem is solved, but also the space for occupying the site is reduced.