Research On Techniques Of Automatic Online Ultrasonic TOFD Imaging Inspection For Girth Weld

The pipeline, known as the carrier of energy transport, mainly depends on the welding to connect. So girth welds have a huge impact on the national energy security, economic development and residents’ life. Meanwhile, as the most vulnerable part of the pipeline, the quality of welds decides the safe, effective and stable operation of the pipeline. And so there is a strong demand for non-destructive testing technology to ensure the safety and quality of girth welds. Ultrasonic TOFD (Time of Flight Diffraction) imaging inspection technology has become an important method of weld quality assessment because of its outstanding technical advantages. After years of development, this technology by artificial method has widely used. However, with the task of weld testing becoming huger, more difficult and dangerous, the artificial detection technology has been increasingly difficult to meet the demand of practical application. Therefore, the technology of automation TOFD ultrasound imaging detection must be developed. For the purpose, combined with the National Natural Science Foundation Project "Research on theory and practice of automatic online ultrasonic nondestructive testing with high performance based on rotating acoustic field (NO.51175465)", the research on techniques of automatic online ultrasonic TOFD imaging inspection for girth welds was put forward in this dissertation.According to the characteristics of the automatic online ultrasonic TOFD testing for girth welds, the model of ultrasonic TOFD detection under the condition of water membrane coupling was established and a method for improving the time resolution of the ultrasonic detection signal was proposed to measure the arrival time of TOFD echoes in the above model accurately. What’s more, image processing technologies were applied to improve the spatial resolution of ultrasonic TOFD imaging, which is contribute to realize the automatic ultrasonic TOFD B and D scan imaging with higher quality and more friendly result. At the same time, an automatic online ultrasonic TOFD imaging detection system for girth welds was successfully developed. The detailed contents of this dissertation were presented as follows:Chapter 1, the great influence of pipeline transport on national economy and human life, together with the important significance of research on techniques of automatic online ultrasonic TOFD imaging inspection for girth welds were introduced. The current research status and development trend of this technique were analyzed and summarized systematically to indicate the direction and main issues for the research of this paper.Chapter 2, based on the principle of ultrasound TOFD imaging inspection, the features about beam coverage and frequency distribution of ultrasonic signal generated by the TOFD probes were interpreted in detail. Besides, the functional goals and the diagram of the inspection system were pointed out and the key technologies to be solved were definite clearly.Chapter 3, the model of ultrasonic TOFD detection under the condition of water membrane coupling was set up. In this model, the computing methods of ultrasonic echoes’arrival time and sizing defects were derived. In addition, a novel sparse deconvolution technique, based on split spectrum sub-band decomposition and SpaRSA algorithm, was employed to improve the time resolution of ultrasonic TOFD detection signal. As a result, the arrival time of related ultrasonic echoes was measured more accurately than the traditional measurement methods. Thus, the above technologies laid the necessary technical foundation for realization of automatic online ultrasonic TOFD imaging inspection for girth welds.Chapter 4, the modified synthetic aperture focusing technique (SATF) was introduced to improve the lateral resolution of ultrasonic TOFD images. Moreover, associated with the lateral wave straightening, calibration processing and sparse deconvolution technique, the testing results of girth welds were presented more hospitable and fairly straightforward.Chapter 5, adopting the distributed architecture and modular design strategy, an automatic online ultrasonic TOFD imaging inspection system for girth welds was successfully developed, whose key modules include hardware components, software components, and mechanical scanning devices. Meanwhile, some experiments were carried out by this system to validate its performance level.Chapter 6, the research results and the innovative points of this dissertation were summarized, and the future research works were forecast.