Magnetic Testing Method And Portable Instrument For Curved Pipe

Curved pipes are widely used in pipeline for changing the flowing direction. Compared with other parts of pipeline, the curved pipe may cause defects more easily, which brings problems to the safety of the pipeline. There is still no high-efficiency, convenient and economical inspecting method for curved pipes inside and outside the country.The thesis researched the separated mode of magnetic flux leakage (MFL) inspecting method based on the characteristic of the structure of the curved pipe. It includes the analysis of the magnetic circuit, the calculation of the intensity of magnetization and the mode of the magnetization. In order to inspect outside defects of the curved pipe conveniently, the thesis advanced the opened magnetic circuit testing method based on local magnetic field and the opened magnetic circuit testing method based on the main flux. Especially, the thesis focused on researching the characteristic parameters'effects on the inspecting signal and the quantitative characteristic of the defects by using the opened magnetic circuit testing method.The sensor based on separated mode of magnetic flux leakage and two kinds of sensors based on the opened magnetic circuit testing method are designed aimed at the inside and outside defects. It developed a kind of portable non-destructive testing instrument for the curved pipe which includes the inspecting sensor, the embedded instrument and the signal processing circuit. The instrument is applied in inspecting of the curved pipe samples of different specs. The results show that the separated mode of magnetic flux leakage sensor can inspect the through hole with dimension ofФ1.6mm and the taper blind hole with the depth of 20% of the pipe's thickness inside the curved pipe ofФ32mm. Also it can inspect the taper blind hole with the depth of 40% of the pipe's thickness inside the curved pipe ofФ219mm. The sensors based on the opened magnetic circuit testing method can inspect through holes with the dimension ofФ3mm on the curved pipe of specs fromФ32 toФ273mm. The sensors have great effect on inspecting the large diameter curved pipes with thick wall especially. The testing result shows that the instrument has some advantages such as the simple structure, convenient operation and high inspecting sensitivity. It can satisfy the requirement of application which has bright application future.