Research On Reconstruction Methods Of Distortion Image Of Weld X-ray Based On Digital Radiography

In the construction of petroleum storage and transportation engineering, the weld NDT(Nondestructive Testing) is the key to the construction process and its quality is the important guarantee for the construction quality, thus, the Ray inspection is the essential means to test the weld quality. The detection of welding spot mainly by the X-ray film photographically all along, but the problems such as high cost, long cycle, low efficiency and pollution are always exist. With the advantages of high detection speed, high detection efficiency, high sensitivity, high resolution and wide dynamic range, X-ray has become a new nondestructive testing method, which is the development direction of nondestructive testing technology. Because of the use of digital imaging plate in X-ray direct digital imaging detection, the space geometry distribution of the spot radiation source and the plane imaging plate and the weld seam is different, and the image of weld seam is evaluated to produce geometric distortion. This paper is studied based on Based on X-ray digital direct imaging of storage tank and pipeline weld image distortion principle and calibration method. Its main contents are divided into the following four aspects:1. X-ray direct digital imaging image acquisition and processing device. Research and analysis of the storage tank weld seam direct imaging device, using the SWSI(single-wallsingle-image) transillumination method to acquire the X-ray image. Research and analysis of the storage pipeline weld seam direct imaging device, using the DWSI(double-wallsingle-image) transillumination method to acquire the X-ray image. Researching the X-ray film imaging digitalizing technologies and methods, and applying the DICOM international standard to unified format storage and description of direct imaging image and film imaging digitalizing.2.The study of single-walled tank weld X-ray shadow image distortion and single gamma correction algorithm. This thesis studies the principle of distortion production in using storage tank weld seam X-ray direct imaging and as can be seen that the storage tank weld seam direct imaging only has single axial linear distortion. The thesis proposes a SWSI distorted image correction algorithm based on back projection. Which uses back projection to calculate the undistorted position on tank walls according to each point acquired in image gathering, to achieve the correction of geometrical distortion. As for the principle of the storage tank weld seam SWSI imaging distortion, grayscale linear interpolation is applied to Gamma correction after back projection.3.Research of pipeline weld seam DWSI imaging distortion and Gamma correction algorithm. This thesis studies the principle of distortion production in utilizing pipeline weld seam X-ray DWSI direct imaging, which applies oblique projection trans-illumination to the pipeline wall to cause a second distortion. This thesis proposes a 3-dimensional Radon transformation and inversion convolution back projection algorithm to apply the geometrical distortion correction. Partial reconstruction of the study of the image is very effective. Finally,a gradation correction bilinear interpolation.4.Digital image and film imaging standard image effect comparative after correction. By making standard image through scanning and digitalizing film image and researching the conformity comparison algorithm of corrected image and standard image, this thesis proposes a measurement method utilizing standard image to compare image similarities. According to a feature image and the standard image of the adjusted value of the row vector composition,calculated by the row vector of the feature vector gray value. Variance calculated based on these gray value, measure the similarities of two images to evaluate the correction algorithm.The results show that the two distorted image reconstruction algorithm this thesis proposes are all feasible.