Study On The Technology Of Magnetic Flux Leakage Inspection For Seamless Tubes

Seamless tubes are widely used in many places, such as pipeline transporting, machinery manufacturing and large-scale construction of venues. So it has a pivotal status in the industry. Any potential defects on seamless tubes can cause an accident. In order to keep the using performance of seamless tubes, they are mainly tested by non-destructive testing technology. Compared with other NDT techniques, MFL(Magnetic Flux Leakage) technology has many advantages. The MFL technology of seamless tubes is studied in this paper. And the main research is as follows:(1) In the overall designing of MFL system for seamless tubes, the testing scheme and the mode of magnetization are designed. According to the actual situation of factory, the layout of testing line and testing process are designed.(2) At first, MFL signal processing system is designed. It includes the selection of magnetic sensor, the designing of MFL signal pretreatment circuit, the de-noising module of MFL signals, data compressing module and peripheral communication module. The extracting of MFL signal character and defect recognizing method are also studied. Meanwhile, loading and unloading module of seamless tubes, flexible magnetizing module, demagnetizing module, defect marking module are designed.(3) At first, the principle of magnetic flux leakage detection is verified by 2D electromagnetic field simulation based on ANSYS system. In order to reflect the actual situation of leakage magnetic field, the 3D electromagnetic field simulation is used to analyse the leakage magnetic field of seamless tube. According to the simulation results, the distribution regularity of leakage magnetic field for no defect seamless tube and defective seamless tube are obtained. Finally, the influences of defects sizes, the intensity of magnetizing coil and the value of lifting off on leakage magnetic field are studied.(4) Firstly, the causes of non-detection zone in the end of seamless tube by using MFL testing are analyzed. The corresponding detecting device and testing line is designed to solve the problem of non-detection zone in the end of seamless tube. And the feasibility of the method is verified by simulation. Finally, the influence of changing permeability of guide seamless tube on the effect of detection is studied.Some of the research achievements have been applied to the company.