The Study Of The Method Of Magnetic Flux Leakage Testing For Longitudinal Flaws Based On Orthogonal Magnetization By Direct Current For Steel Pipes

As the rapid development of oil chemical industry and basic contribution project in China, the need of steel pipes is growing at very fast speed, and the requirement of the production efficiency is higher and higher. It takes urgent requirement of high-speed and over-high-speed magnetic flux leakage non-destructive testing for steel pipes. Steel pipe spiral movement or devices rotating scanning was used to detected defects by the magnetic flux leakage equipment, thus high-speed magnetic flux leakage testing of steel pipe was constrained. A new magnetic flux leakage method based on the DC orthogonal magnetization was developed in this dissertation. This method does not need to revolve the steel pipe or equipment, may realize high speed detection of longitudinal flaws of steel pipe. The method was of fast, reliable, has overcome the manufacture difficulty of high accuracy, the high kingbolt and the link system.The dissertation has contrasted on many experiments by many kinds of probe and scanning way. The result indicates the piece inductance is suitable as magnetism sensitive detecting element for this examination method. The longitudinal flaw of steel pipe, 25mm(length)×1mm(wide)×0.5mm(depth), can be detected, and magnetizer's circumferential effective magnetization scope for 240°and the single detecting element's circumferential effective detection range for 20°has determined.According to the influence factors of longitudinal flaws detection of pipes and the experimental results, the author designs the equipment of Magnetic Flux Leakage Testing for longitudinal cracks of steel pipes. The equipment includes the orthogonal magnetization equipment by direct current, the probe, the signal amplification circuit and post-processing system. The orthogonal magnetization equipment is made up with two magnetization unit. The probe, which is applied to multi-specification pipes, can be centered automatically and keep following favorably. And the collocation mode of the probe inside detecting elements is designed.The longitudinal flaw of the steel pipe, 25mm(length)×1mm(width)×0.3mm(depth), can be detected with the equipment. The result indicates that this equipment has high detecting sensitivity and good stability, and is provided with great abroad application foreground.