Research On Magnetic Flux Leakage Testing Methods For Petroleum Pipe Tool Thread

Pipe tools used in oil field can fail by defects such as rupture, thread abrasion, and crack in the thread area, under the chronic and atrocious working environment. These types of defects must be detected by periodic inspection to estimate the remaining life of the pipe tools and avoid accidents in the field. As there is still no effective and reliable inspecting and evaluating method, a new Magnetic Flux Leakage testing method, Separate Magnetic Flux Leakage (SMFL) testing method is introduced, which can inspect such specific and anomalous work piece as pipe tool thread.In the SMFL, the magnetizer and the magnetic inducer are two independent parts and work separately, the magnetizer magnetizes the work piece to saturation and the magnetic inducer inspects the magnetic flux signal produced by the failure. This method combines the advantages of the traditional MFL testing method and Magnetic Particle Testing method, avoiding each limitation. It can inspect the specific and anomalous work piece with little blind area instead of the Magnetic Particle Testing method. Several inspection models are brought forward according to the specific geometrical configuration of Drill string thread, tubing thread, suck rod screw, coupling collar and so on. The distribution of each inspection models and the effects of magnetizing system parameters on the pipe tools thread are studied by the numerical computing technique. Result show that the SMFL is an effective inspection method to inspect the flaw in the pipe tools thread area.Based on the configuration of tubing thread and according to the experimental research, several SMFL inspection methods are analyzed and compared and only one is the most suitable method to inspect the tubing thread quickly, exactly and reliably, in which the magnetizer is fixed inside the end of tubing with yoke to magnetize the tubing thread area and the magnetic inducer scans the tubing thread surface along the axial direction to induce the magnetic signal of flaw. The Hall sensor disposal method and the signal processing method of tubing thread inspection signal are researched and conclusions are summarized. Finally, according to the experiments and optimization results, the tubing thread inspection transducer which combines magnetizing system and detecting system, is then designed. Experiments show that the transducer has good sensitivity and reliability.As the difference of drill string thread and tubing thread configuration is very large, the two inspection methods must been researched with much difference. Drill string has much larger thickness and tooth height than those of tubing thread, so the magnetizing method and magnetic inducing method are different absolutely. Comparing the experimental result of several inspection SMFL methods and taking the spot requirement into account, the most suitable method to inspect the drill string thread is put forward, in which the coil magnetizer is fixed outside the drill string apart from the thread area and the magnetic inducer scan the thread area along the screwy direction of the thread to induce the magnetic signal of flaw. Quantitative analysis technique of the crack in the root of tooth is detailed. According to the experimental research and optimization result, the drill string thread inspection transducer is then designed, including the magnetizing system and detecting system. Experiments and testing show that the inspection equipment and system has good quality and product performances and it can be used in the field conveniently.In a word, a new magnetic inspection method is put forward and two kinds of inspection equipments that is tubing thread inspection equipment and drill string thread inspection equipment and system are developed in this thesis.