Method for accurate detection of material defect and thickness by using digital radiography transillumination technology

Abstract

The invention provides a method for accurate detection of material defect and thickness by using a technology of digital radiography transillumination, and belongs to the field of nondestructive test. A test block with fixed gradient is placed on a material to be detected, a radiation field from top to bottom passes through a workpiece to be detected and the test block with fixed gradient at the same time, a digital ray reception plate receives attenuated ray, and the ray is converted into a two-dimensional image by a data displaying and processing unit. According to a flat weld detection, the test block with fixed gradient is placed beside the workpiece to be detected; the cross section of the test block is a right trapezoid, wherein a right-angle side is horizontally placed on the horizontal plane same to that of the workpiece; according to a small diameter tube detection, a test block with gradient is used, and the cross section of the test block along the axial direction of the test block is semi-toroidal, and the cross section of the test block along the circumferential direction is right trapezoid; internal diameter of the test block with gradient is equal to the external diameter of the small diameter tube, and the cross section of the test block with gradient is semi-toroidal, the test block is tightly wrapped outside the workpiece to be detected and is placed beside the weld. The method can be used for accurately measuring height of the defect and weld reinforcement or the like without misjudgement.

Description

Technical field [0001] The invention discloses a method for accurately detecting defects and thicknesses of materials by digital radiographic technology, and belongs to the field of nondestructive testing. Background technique [0002] 1. Industrial radiography technology [0003] Radiographic inspection is a kind of non-destructive inspection, including X-ray inspection, γ-ray inspection, high-energy ray inspection and neutron ray inspection. For industrial ray inspection, X-ray inspection and gamma ray inspection are generally used. The principle is: when a beam of uniform intensity irradiates an object, if there is a defect or a difference in structure in the local area of ​​the object, it will change the attenuation of the object to the ray, so that different parts of the transmitted ray have different intensities. In this way, a certain detector is used (For example, film is used in radiography) by detecting the intensity of transmitted rays, it is possible to judge the defe...

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Problems solved by technology

[0024] 2) Measurement error: Generally, the defects that need to measure the depth in the workpiece are thin-line, and the characteristics displayed on the film are thin black lines, such as incomplete penetration, incomplete fusion, undercut, etc., the width of such defects Generally below 0.5MM or even smaller, while the groove width of the groove-type comparison test block is 2MM. For the blackness meter used for measurement, the dotted needle is at the millimeter level. When used to measure the blackness of the groove-type test block groove , can find its position, when measuring the blackness of the defect, it is often difficult to find its position, one is that the width of the defect is much smaller than the width of the needle, and the other is that the film is black under natural light, and it is difficult for the human eye to distinguish the exact position of the defect , so the measurement error is large

This situation will cause the user to be unable to confirm the precise location of the comparison during reality detection

[0029] 3. More importantly, there is a possibility of misjudgment (inaccuracy) in the above two methods:

However, during on-site inspection, when the unfused defects with a fixed height appear in the residual height of 2mm and 1mm, the final gray level will definitely be different, which may lead to different rating results when compared with the test block

[0031] However, the latest standard NB / T47013 issued in April 2015 (replacing the latest version of JB / 4730, implemented on September 1) requires consideration of the difference in the height of the reinforcement, and according to the height of the height of the reinforcement (the thickness of the test block is equal to the height of the height of the reinforcement). Make a test block, but still use the gray scale contrast method of the stepped test block

However, the welding environment and personnel differences in the actual site determine that the reinforcement range is very large, and the reinforcement height fluctuation of the same weld is also relatively large, so it is difficult to determine the height of the test block; for example, when the weld seam fluctuation is large, how to make The reference block does not specify

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