Research On Key Techniques Of External Scanning Phased Array Ultrasonic Imaging And Quantitative Detection For Steel Pipes

Steel pipes, widely applied to engineer practice as an economic steel, have huge impact on national economy and people's lives, and the quality directly determines the operating performance and service life of related equipment, so the demand for non-destructive testing (NDT) has always been very strong. In a variety of non-destructive testing methods, ultrasonic NDT, with its high safety, rich acoustic information and various combination to information technology, has become an effective means of quality control for steel pipes, and is moving towards the quantitative evaluation of phased array ultrasonic technology. Especially, besides the common advantages of ultrasonic NDT,phased array ultrasonic NDT also has a flexible synthetic beam and adaptive control capability, and can effectively reduce the blind zone, which possesses a definite technological advantage in steel pipe inspections. According to the background above,supported by the National Science Foundation Project "Research on theory and technology of automatic online phased array ultrasonic imaging with high performance for cylindrical components (NO.51675480)", the research on key techniques of external scanning phased array ultrasonic imaging and quantitative inspection for steel pipes is put forward in this dissertation. Based on analysis of related theory and inspection methods, phased array imaging and quantitative inspection methods are proposed to solve the problem of the quantification of defects. What's more, combined with mechatronic technique, an external scanning phased array acoustic imaging and experiment inspection system for steel pipes was developed, and related experiments was carried out, laying a theoretical and applied foundation for external scanning phased array imaging and quantitative inspection for steel pipes. The detailed contents of this dissertation were presented as follows:In chapter one, the importance effect of steel pipes in national economy and people's lives and the research significance of key techniques of external phased array ultrasonic NDT for steel pipes are introduced, and the research status and development trends of phased array ultrasonic imaging technique and quantitative inspection are systematically summarized. The problems on technology of phased array ultrasonic imaging inspection for steel pipes are pointed out to clarify the main research of this paper and indicate the direction for the following chapters.In chapter two, the wave equation and its solution in cylindrical coordinate system are established to analyze the acoustic effect of acoustic wave propagating in steel pipe and the influence of acoustic effect on imaging resolution. Based on the plan of steel pipes inspection, the study of phased array ultrasonic beam forming and designing the wedge are proposed to achieve the beam focusing in the steel pipes. Meanwhile, the radiation field of a phases array transducer is calculated and analyzed.In chapter three,The B-scanning and S-scanning are two main scanning methods of phased array ultrasonic imaging with clear presentation. Besides, to achieve the rapid scanning imaging with high efficiency and large-scale on the specimen, this chapter presents a compound scanning technology based on the combination of mechanical scanning and electronic scanning imaging.In chapter four, the ultrasonic imaging preprocessing technology is researched. The wavelet threshold de-noising and image interpolation are used to eliminate the noise interference to improve the noise-signal ratio. In addition, -6dB quantitative technique is applied to obtain the shape and size of defects to achieve quantitative detection of defects.In chapter five, based on the distributed architecture and modular design strategy,with self-research and development of the phased array ultrasonic testing instrument as the core component, after processes of hardware design and software development, an external scanning phased array acoustic imaging and quantitative inspection prototype for steel pipes is successfully developed. Meanwhile,the practical experiment of seamless steel pipe is performed on this system to verify the feasibility and effectiveness of relevant theory and techniques proposed in this dissertation.In chapter six, the research achievements and the innovative points of this dissertation were summarized, and the future research works were also forecasted.