Research On Some Key Technologies Of MFL Inspection

Based on the fact that some physic quantum would be changed because of existing defects, nondestructive testing (NDT) could detect the defects. NDT plays a important role of quality controlling and saving raw materials and improve productivity in industry manufacture. NDT is also a important inspection means for the equipment.As one of the most important, fastest and cheapest nondestructive testing methods, Magnetic flux leakage technology could be applied in inspection ferromagnetic materials. MFL is also the most commonly used in nondestructive testing and it could find the majority of discontinuities.The main research contents in this paper include:First, the undetectable area in seamless pipeline (pipeline heads) is usually inspected by magnetic particles, but magnetic particles merely inspect the defect near pipelines' outer surface. The particle indication of defects is usually observed by eye, and so the testing reliability has a high human factor influence depending on the operator. For the reason of equipment itself, MFL inspection equipment couldn't inspect the pipeline heads, which are regarded as an undetectable area in MFL examination. In this paper we attempt to use a new method based on MFL to inspect pipeline heads. We introduce the idea of leading pipeline, and expatiate the method of separating the MFL signal of defect near pipeline heads. The difference between reference signal and artificial flaw signal can be extracted properly by using correlation canceling. The experiments show that it is possible for MFL technology to inspect the tube head, and improve the inspection efficiency.Then, influenced by the lift-off value between the pipeline and coil sensors, the various properties of electronic component and the different location of coil sensor, the output signal's amplitude and phase of each channel are different despite the same flaw in MFL inspection. The channel-to-channel mismatch may severely degrade the performance of testing equipment and disturb the evaluation of the level of flaw unless some form of compensation is employed. In this paper an adaptive method for channel equalization in MFL inspection is presented, we selected a channel as reference channel and used finite impulse response (FIR) filters to compensate the difference between the reference channel and other channels. Both theoretical analysis and experimental results have shown the effectiveness of the proposed method.And then, we summarized the development of the magnetic dipole, and proposed a method which be used to reconstruct the defect's shape. We reconstructed the delta shape, semicircle and rectangle shape defects to illustrate the proposed method. Compared with the other methods, the reconstructed results have shown the merits of the proposed method.Finally, aiming at the research status quo in MFL inspection, we brought forward the new research directions.