1前言在我国现行标准中，对于小直径管环缝双壁双影一次透照时的“有效评定范围”有这样的规定：“计算方法如下：先在底片上测量椭圆影像两侧黑度低于规定值的焊缝长度，再除以整圈焊缝总长，所得百分数若小于或等于10%，则认为有效评定区范围达到了90％以上”。那么有效评定? 1 Preface In the current standards in our country, for small diameter double-wall double-slit double-wall double-shadow double-shadow transillumination, the “effective assessment of the scope” there is such a requirement: “The calculation is as follows: First on the film measured on both sides of the ellipse darkness is low The length of the weld at the specified value, divided by the total length of the entire weld, if the percentage obtained is less than or equal to 10%, then the effective assessment area is considered to have reached more than 90%. ” So effective evaluation?