Large-diameter steel pipe is characterized by large-diameter steel pipe diameter, wall thickness is relatively thick, so taking advantage of this feature based on ultrasound and eddy current testing internal surface and subsurface features combine to achieve "blind" testing. Through the use of "in situ pipe rotation detection probe forward combinations", not only to solve detection problems, but also solve the narrow space occupied space. Therefore, at home and abroad for large diameter steel pipe testing, the general method of magnetic flux leakage or hydrostatic test. In the country, there is no well-functioning suitable for large diameter steel pipe magnetic flux leakage detection equipment produced, the use of which requires entrance. Entrance magnetic flux leakage detection equipment is expensive for the majority of domestic enterprises is difficult to accept; while the hydraulic test inefficient, labor-intensive, especially when the operator is not high sense of responsibility, pressure maintenance useless. Visible to achieve large-diameter seamless steel pipe industry, metallurgical testing has become an urgent issue.
Tank ultrasonic testing is used in the steel spiral forward type, ultrasound probe stationary. Was seized by the sink and the water pipe at the bottom of the full coupling characteristics, to ensure the thickness of the coupling constant. However, due to internal defects detected ultrasonic mainly on the surface and sub-surface defects exist blind, preventing detection, coupled with spiral forward type, 12m long pipe needs for space 30m venues such as inadequate pipe detection method has affected the selection and promotion. Through the coil eddy current probe is a circumferential surface of the pipe surface. Through the use of eddy current coils, the larger the diameter of pipe to be detected, detection of the circumferential area of ??the coil the greater, the lower signal to noise ratio. Is precisely for this reason, pipe eddy scales delineated using eddy current through the coil of its foreign economic size not greater than 140mm. In addition, the large-diameter pipe through the type testing, the pipe magnetization and demagnetization and so there is a certain degree of difficulty.
At present China's metallurgical industry, the high-pressure boiler seamless steel tubes mainly used in φ160mm detect the following specifications, and most of the traditional eddy current through the coil or a separate sink ultrasonic detection methods. For more than φ160mm seamless steel pipe using the traditional method through the eddy current testing, there are still many problems, but also the national scale are not allowed. If using an independent ultrasonic testing, ultrasonic testing mechanism because there is a certain depth of the blind, the overall test results can not guarantee the reliability of steel. In testing technology, large-diameter seamless steel pipe is the pipe diameter greater than φ160mm. Large diameter seamless steel pipe for oil, chemical, thermal, boilers, machinery and other industries important hydraulic timber. Followed by the development of the national economy, our country in the "Eleventh Five-Year" period, a substantial increase in the demand for seamless and significantly showing the development trend of large diameter. Especially for the requirements of anti-erosion, anti-extrusion of OCTG and large-diameter high-pressure boiler tubes and high quality oil cracking pipe, petroleum and petrochemical pipelines pipes, etc., will follow the national measures based initiatives for energy increased investment demand and become Popular.
