Research On Microwave NDT Of Surface Defects On Metallic Parts

The development of the quality supervision, inspection and quarantine career in the twelfth five-year plans was established by State Administration for Quality Supervision and Inspection and Quarantine (AQSIQ). It called higher request on the technical reserve and research, which includes the development of test career, key and practical technology, independent innovation and forward-looking research. Now, it poses a great challenge to existing technology. For one reason, there is an imbalance between the increase of special metal equipment and the insufficient of test power. For another, the way point by point of NDT on metal pipe is inefficient. Research on this paper is from technology innovation and personnel support project, in Taiyuan, Shanxi Province. It has support from the state and Taiyuan University of Technology Research.In this paper, advantages and disadvantages was compared among the existing NDT technology, based on the characteristics of penetration for the metal and the characteristics of non-penetration for the metalloid. The new method is NDT of surface defects on the metal with microwave. The detection method is simple without coupling agent, can be a new method to realize long-distance detection and rapid detection on long distance pipeline, which made prospectively studies for NDT technology reserve. The research content mainly divided into the microwave NDT mechanism research and experimental research.From the study of the microwave technology and its transmission system, microwave NDT mechanism was proposed. On this basis, two sets of microwave NDT system were built for the metal plate and metal pipe inner surface defects, the response signal of defect location and defect size was to be obtained, and its response law was described in this paper. The conclusions are as follows:(1) The microwave NDT device system on metal plate surface defect can be used for metal plate surface defects with of the positioning, which can be characterized by emission coefficient or return loss. When rectangular probe met metal surface defect to detect metal plate by the reflection method in particular frequency band, higher order mode is aroused and return loss becomes higher;(2) The reflection method was using on the NDT of metal plate surface defect, the defect size (width, length, diameter) parallel to surface is characterized by return loss, the defect size (depth)perpendicular to surface is characterized by parameters phase shift.(3) The response signal of defect size is related to wavelength, which is called "a quarter wavelength law" in this paper. On the one hand, the change of return loss with depth change appears volatility, when the width of bar defect is1/4λ or2/4λ On the other hand, the response frequency of the max return loss exchanged with the response frequency of the min return loss, when the depth of the bar defects is closed to1/4λ, and according as this standard, the depth of the defects can be judged.(4) The metal pipe inner surface defects (welding defects and to crack of ring) location and multiple defects detection were realized by the microwave NDT device system on metal pipe inner surface defect. The accuracy of double port detection system detection is higher than single port system, but the latter should be used for the testing of long pipeline;(5) The characteristics signal of defect location is electric length, with the NDT of metal pipe inner surface defects, which presents linear relationship with the actual distance from port. When the pipeline inner surface is close to exist apart of two or more defect, the defect location is affected, which was called "a distortion". And the response of reflection coefficients on depth is higher than the one of width.In short, it is an important effect on NDT technology for the further study on microwave NDT that the response signal of defect was extracted, which has important significance on the NDT technical reserve and key and practical technology.