Large - caliber seamless steel pipe testing technology

　　In the field of detection technology, large diameter seamless steel pipe refers to the diameter larger than 160 mm. Large-diameter seamless steel pipe is important material ofpetroleum, chemical, thermal, boiler, machinery, and hydraulic industry, etc. With the development of national economy, our country during the period of "11th five-year plan", greatly increasing demand for seamless steel pipe, and presents the development trend of large diameter significantly. Especially for corrosion resistance, resistance to squeeze oil well pipe and large diameter high pressure boiler tube and high quality oil cracking pipe, petroleum and petrochemical pipeline, etc., will be as countries increase as demand for energy infrastructure investment hot spot. Thus, to ensure the quality of products nondestructive testing put forward the methods and techniques on the new topic.

　　At present, China's metallurgical industry for high pressure boiler seamless steel pipe detection mainly applied in phi 160 mm below the specification, and adopting the traditional eddy current flaw detection coil or independent water trough type ultrasonic testing method. For more than 160 mm seamless steel pipe through the traditional type eddy current method is used for testing, there exist many problems, also not allowed to the national standard. If use the ultrasonic testing of independence, due to the ultrasonic detection mechanism of the existence of certain depth on the surface of blind area, can't be guaranteed the reliability of test results as a whole.

　　Through the coil of eddy current detection is a circle on the surface of the steel pipe surface. In use through the coil, eddy current flaw detection of tested steel tube diameter, the greater the coil detection, the greater the peripheral area of the lower SNR. It is for this reason, steel pipe eddy current inspection standard, adopt through the coil, eddy current flaw detection of its foreign economic size shall not be greater than 140 mm. In addition, in the large diameter steel pipe through the type testing, the steel tube of magnetization and demagnetization, there is certain difficulty.

　　Water tank type ultrasonic testing is to use steel pipe spiral advancing, ultrasonic probe fixed. By the sink and checked the characteristics of the steel pipe full of water at the bottom of the coupling, ensure that the thickness of the coupling layer remains the same. But for ultrasonic detection of internal defects on the surface of main surface defects exist blind area and time, lead to cannot detect, coupled with the spiral advancing, 30 m to 12 m long steel pipe need to occupy a space of venue, etc, have been affect the choice of the steel pipe detection method and promotion.

　　Therefore, testing for large diameter steel pipe at home and abroad, generally using the magnetic flux leakage method or the water pressure experiment. At home, it is no good performance for large diameter steel pipe produced by the magnetic flux leakage detection device, once used to import. Imports of magnetic flux leakage detection device is expensive, difficult to accept for most of the domestic enterprises; And low efficiency of water pressure test, the intensity of labor is big, especially when the operator the sense of responsibility is not high, the water pressure test. Visible, realization of large diameter seamless steel tube inspection has become a subject urgently to be solved in metallurgical steel pipe industry.