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Pressure pipes of small diameter pipe butt weld defects in radiographic detection method of the negative factors and improvement measures

Clarity and granularity. 2.1 contrast. The main factors that affect the contrast of the thickness difference through the photos, ray energy and scattering ratio, film type, film blackness, development conditions. Enhance the contrast radiography of small diameter pipe the main way the formula by the negative contrast △ D = 0.434GzAT / (1 +, 2) can be seen that: ① increased value. In ensuring the penetration of the premise, should be adopted in low-energy radiation, but this would increase the exposure time. ② increase the G value. Higher G values can be selected particulate film. ③ increase the black level. Because non-sensitized film G value and the black level is proportional to the black film can also be improved to increase the degree of G values, but the high value of the particle G Film more slowly, increasing the exposure time required to improve the black level is also need to increase the exposure time, in addition, increase the black level will increase the minimum visible contrast △ D, on the sensitivity of negative factors. To this end, consider the small-diameter oval tube through a large thickness tolerance according to the characteristics of film on the weld and heat affected zone of the black level should take 2. O ~ 3.0. ④ lower-ray energy. Choose a lower energy rays can get higher contrast, but it means higher contrast transillumination lower thickness tolerance. According to small-diameter pipe through the penetration when the rays from the center to both ends of the changes in the thickness of a large, easily lead to negative degree on the center of the black, the black edges is small, the decrease was seized in different parts of the black area is poor, should be appropriately increasing the beam energy, but with the-ray energy increases, will inevitably lead to lower contrast, the inherent unsharpness increases, the film grain size increases, resulting in decreased sensitivity, so the premise of ensuring penetration, should be use low-voltage,[link widoczny dla zalogowanych], and by increasing the number of transillumination transillumination to solve the problem thickness tolerance. ⑤ decrease the value. To reduce the scattered radiation, it is necessary the use of lead and lead shielding windows, put a window in the ray with lead shield shielding plate or other part of the weld, need the use of lead foil to reduce the scattering of screen lines, and shelter should be used irradiated directly in that part of the film were screened to reduce the edge loss scattering. Definition 2.2 U by the formula of a geometric definition dL. / L known, geometric clarity of the main factors are: the focus size, focus to surface distance, the distance from the surface to the film. The inherent unsharpness of the main factors are: beam energy, type of screen ① focus size. The geometric dimensions proportional to the clarity and focus, focus size is smaller, the smaller geometric sharpness. As the structural causes of X-ray tube, at different positions along the axial ray tube focus projection size change, the focus of a small anode side and cathode side of the focus of large, so the film would be more inclined than the value of the anode side of the cathode side of the small, so small-caliber tube anode side of the shift to shift the direction of geometric clarity smaller, but because of directional emission X-ray tube X-ray beam with 4O. About three-dimensional cone angle, and anode-ray intensity is weak, the cathode ray intensity stronger, but contains more of the soft-ray elements, so should the anode side of the pan, but it should be noted that after the point of translation is not too large, otherwise easy to appear bald in the film phenomenon, affecting sensitivity ② focus. In order to obtain a smaller value, through photos taken when the need for greater focus on the F,[link widoczny dla zalogowanych], at the same time reduce the intensity of light rays inside the uneven quality of the camera, the focal length should also take bigger is better. ③ ray energy. Because of the inherent unsharpness with ray energy increases,[link widoczny dla zalogowanych], so the rays will lead to the increase in energy resolution and the lower energy and will reduce the thickness tolerance through photos, so to ensure penetration and to consider thickness tolerance of the premise, as far as possible the selection of low voltage and increase the number of times through the photos, but it must extend the exposure time to accommodate a larger focal length. 2.3 The impact of particle size particle size radiographic film types of the main factors, beam energy, developing conditions, it needs to be taken to improve the sensitivity gradient of large, low grain, high SNR and slow light-sensitive film, a more low beam energy,[link widoczny dla zalogowanych], but the need to increase exposure. In summary, to improve the small-diameter pipe butt weld quality camera,[link widoczny dla zalogowanych], you should use a smaller-ray source focal spot size, penetration in the premise of ensuring to make use of low energy X-ray tube voltage, in terms of permitting Radiographic case of increase in the number of radiation machines in the window or put a plate cover with lead shielding to reduce the scattering of the weld line than some of the impact of increasing the focal length and a large selection of graded film of particles, control the thickness of X-ray Radiographic oval opening that is controlled 3mm ~ 10mm spacing in between to prevent distortion of the image defect. Through a combination of these means can the radiographs have high sensitivity and increase small and medium small-diameter pipe butt weld defect detection rate. References: [1] Strong Tianpeng. Ray detection. Kunming: Yunnan Science and Technology Press.

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