Research On Digital Radiographic Inspection Technology On Tube To Tube-sheet Joints

The Tube to Tube-sheet joints are the main connection structure of the heat exchanger and the reactor. For a long time, traditional photographic film was used in the detection of welded joints, but it brought with the problems of film storage and environmental pollution, however Digital Radiographic technology completely solved these shortcomings. This paper is based on the traditional film-ray imaging principle, and combined with modern detection technology. A rotary scanning system was designed, the key technology was researched and the detection was realized based on Digital Radiographic technology on Tube to Tube-sheet joints.The innovations in this paper are: a control system was designed to carry linear array detector rotary scanning around the weld; a mathematical module of rotary scanning graphics reconstruction was built, an image processing software was compiled. Eventually experimental prototype had been developed, resolution test card and image quality indicator were used to detect the imaging accuracy and quality. The prototype was used to scan the Tube to Tube-sheet sample, analyze the defect in weld and the expected result was achieved. The System resolution is better than 5LP/mm(LP=LinePair), and the image quality is B-class level to film, so the feasibility of selected scheme is proved.The main work in this paper contains several aspects as described as follows:1. According to the characteristic of the defects which Tube to Tube-sheet joints might have, referring to the mature film imaging detection systems, including comparative analysis of the existing Digital Radiographic technology, ultimately it was decided to adopt the general scheme that: the linear array detector would be controlled to rotate around the weld, and output scanned data into the computer for follow-up treatment.2. In order to precisely control the movement of linear array detector, a machinery agency and motion control system was designed. System load was computed for selecting the appropriate models of motor and driver.3. A mathematical model of rotary scanning graphics reconstruction was set up, which implemented the mapping from scanned image in polar coordinate system to reconstruction image in rectangular coordinate system based on the Plane Fitting Algorithm. The experiment results indicated that the precision and reliability of the system was ensured by this mathematical model.4. A software was complied to control the system and realize the acquiring, processing, archiving images and other operations. The measurement modules could estimate the size of defects and judge the type .