The Characteristics Of Weld Buried Defects Causing The Leakage Of Magnetic Field And The Study Of Detection Signal Analysis

With the rapid development of our country’s national economy, China’s consumption level of energy such as oil, natural gas is becoming higher. As the important connection part of welding equipment such as tank bottom plate, pressure vessel, pressure pipeline, weld is prone to defects in the process of manufacture and use. So it’s very necessary to test the weld structure. At present, welding nondestructive testing changes rapidly due to technical factors, rules and regulations and economic.In recent years, both at home and abroad are seeking for weld detection method which is more suitable for weld defects detection. With the raise of weld magnetic powder detection reliability problems, the application of magnetic flux leakage testing method in weld detection has received more attention. Due to the results of the magnetic flux leakage testing methods have quantifiable characteristic, and the reliability of the result is relatively high, it also has high efficiency as well as the advantages of less pollution, so in this article weld buried defects is detected by the method of magnetic flux leakage testing.This article mainly aims at the characteristic of tank bottom plate weld, study the method of weld magnetic flux leakage testing. The main research methods of this paper is the combination of theory analysis and laboratory experiments.In this article, the electromagnetic field theory and the finite element theory were mainly applied in analysis, use the finite element software to establish the finite element model buried in weld defects in magnetization state, and leakage magnetic field distribution and influencing factors of buried steel weld defects were analyzed.This paper analyzed the parameters of hidden defects in weld, mainly the influence of depth, diameter of leakage magnetic field; Also analyzed the impact of weld residual height on leakage magnetic field.The buried defects in the weld of experimental steel plate were processed under laboratory conditions, using weld leakage detector for a series of experiments, the leakage magnetic field experimental data of plate defect was collected, and data comparison analysis was conducted. The signal data obtained was analyzed by the method of mathematical morphology. After handling the signal by morphological,the gray image was obtained; Then sharpening the image, so that we can get more distinct image; Make binarization operation on image sharpening processing result, the purpose is to prepare for subsequent processing; Refine the obtained image, then use the method of morphological to handle image, some characteristics of the buried weld defects could be obtained.