Research On Detection Technology Of The Welds Of Small-diameter Tube Based On Weak Magnetic Testing

Small-diameter tubes are widely used in electric power equipment, and most tubes are joined by welding. Transporting medium is the most common function of small-diameter tube. Long-term operation with pressure, poor working conditons, will bring great challenge to the welding quality, which requires quality inspection both in the process of welding and long-term operation. Under the traditional testing conditions, the total coverage detection of small-diameter tube welds requires the combination of various detection methods, which will lead to low efficiency. In view of this, the application of weak magnetic testing in the detection of small-diameter pipe weld is proposed in this paper, which can detect the common types of defects efficiently.Firstly, the technical principle of weak magnetic testing and the feature of small-diameter tube welds were analyzed in this paper, which pointed the detection difficulty of small diameter tube weld, and its feasibility of weak magnetic testing was proved by the simulation calculation. Three detection schemes were proposed based on the geometric shape and signal characteristics of small-diameter tube welds: detecting the normal component of signal by ratating tube, detecting lateral signal by scanning and detecting the normal component of signal by scanning. Then, two test specimen of small-diameter tube were tested by the portable instrument of weak magnetic detection, and the results of the three detection schemes were analyzed. The results and curves of the first two detection schemes were more obvious, and simple defect evaluation could be accomplished by experience. When using the third detection scheme, the interference signal of the background magnetic field can be eliminated by wavelet analysis, and the defect signal were extracted effectively. The results of each detection scheme were compared with the results of X-ray detection, which verified that schemes were effective, and the advantages and disadvantages of each scheme were summarized.Finally,in order to solve the difficulty of defect qualitative,this paper presented a kind of defect recognition algorithm, which can reduce the error caused by experience to judge. Defects were classified into two major categories of crack and porosity. A defect classification model was established based on the distance discriminant analysis method, and the wavelet packet energy spectrum was chosen as the characteristic parameter of the defect. Discriminant functions were obtained through training weld defects samples of small-diameter tube, and other 20 samples were tested, showing that the recognition accuracy of the porosity is 70%, and the recognition accuracy of the crack reaches 90%, which verifie d the validity of the model. The research of the weak magnetic detection scheme and the defect recognation technology provide new methods and ideas for the detection of small-diameter tube welds.