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透照厚度比K值是指一次透照长度范围内射线束穿过母材的最大厚度与最小厚度之比。一次透照长度是指采用分段曝光时,每次曝光所检测的焊缝长度。控制焊缝一次透照长度范围内射线束穿过母材的最大厚度与最小厚度之比的目的,一是为了控制一次透照长度范围内的焊缝横向裂纹检出角,防止接头横向裂纹漏检。二是为了确保焊缝一次透照长度范围内的底片黑度均匀、并在标准规定的范围内。JB/T4730-2005.2对“一次透照长度”的表述是:“一次透照长度应以透照厚度比K值进行控制。不同级别射线检测技术和不同类型对接接头的透照厚度比应符合规定见表1。
Transillumination thickness ratio K value refers to the ratio of the maximum thickness and the minimum thickness of the beam passing through the base material in a transillumination length range. A transillumination length refers to the length of the weld that is detected for each exposure with segmented exposure. The purpose of controlling the ratio of the maximum thickness and the minimum thickness of the beam passing through the base metal within a transillumination length range is to control the detection angle of the horizontal cracks in the weld within the range of the transillumination length and to prevent the horizontal cracks of the joint from being missed . The second is to ensure that the penetration of the weld within a single length of the film black uniform, and within the scope of the standard. JB / T4730-2005.2 The expression ”a transillumination length“ is: ”The transillumination length should be controlled by the transillumination thickness ratio K. The transillumination thickness ratio of different levels of radiographic techniques and different types of butt joints Table 1 should be complied with.