Flaw analysis of large diameter thick wall seamless steel pipe

At present China's metallurgical industry, the high-pressure boiler pipe mainly used in the detection of 160 mm the following specifications, and most of the traditional eddy current through the coil or a separate sink ultrasonic detection methods. For more than 160 mm seamless steel pipe using the traditional method through the eddy current testing, there are many problems, but also the national standards allowed. If using an independent ultrasonic testing, ultrasonic testing mechanism exists because the surface of a certain depth of the blind, the overall test results can not guarantee the reliability of steel.

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. It is for this reason, pipe eddy current testing standards, the use of eddy current through the coil of its foreign economic size not greater than 140 mm. In addition, the large-diameter pipe through the type testing, the pipe magnetization and demagnetization and so there is a certain degree of difficulty.

Tank ultrasonic testing is used in the steel spiral forward type, ultrasound probe stationary. It 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. But because ultrasonic detection of internal defects on the surface of the main and sub-surface defects exist blind, preventing detection, coupled with spiral forward type, 12 m long pipe needs for space 30m venues such as inadequate pipe detection method has affected the selection and promotion.

Therefore, the domestic large-diameter steel pipe for testing, generally using magnetic flux leakage or water pressure test. In the country, there is no good performance for large diameter steel pipe magnetic flux leakage detection equipment produced, the use of which is imported. Imported 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, the water pressure test useless. Visible to achieve large-diameter seamless steel pipe industry, metallurgical testing has become an urgent issue.

Is characterized by large-diameter steel pipe diameter, wall thickness is relatively thick, so take 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 to solve narrow space occupied space.