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Cracks are planar defects in two-dimensional space, usually with very small widths. Directionality is particularly evident in radiography. It is not easy to detect when the ray penetration direction is perpendicular to the crack, because the contrast on the film is very small. When the direction of X-ray irradiation is parallel to or at a small angle to the direction of the crack, it is easy to detect. The crack appears as a relatively clear image on the film, slightly wider in the middle and narrower at both ends; sometimes it is zigzagged and toothed, making it easy to identify. Non-welding: For groove edges with larger specimen thicknesses, both non-welding at the edges and interlayer non-welding are difficult to detect using radiographic inspection. Undergoose in medium and thin plate grooves is also difficult to detect using radiographic inspection; when the radiation beam is directed along the weld groove, fine black lines may appear on the film. Most detectable unfused defects are accompanied by inclusions; on the film, their characteristics show one side that is straight while the other is irregular. The darkness of the defect itself is relatively uniform, forming a line of certain width located on the side of the weld image. The aforementioned characteristic defects often occur in automatic welding cases of misalignment. This is because the thickness of the unfused defects, which contain no inclusions, along the direction of the radiation beam is very small; as a result, the reduction in radiation intensity due to these defects is only slightly different from that in defect-free areas. This results in a small difference in density on the film, making it difficult to detect such defects ； The thickness of the unfused defects containing inclusions along the direction of the radiation beam is relatively large, and the contrast on the film is also high, so they are easily detected. In another case, at the root of the butt weld of the pipe, the lack of fusion is significant; on the film, this appears as black patches that are straight on one side and irregular on the other. Underflow: In radiographic inspection, underflow occurs at the root of single-sided welds and in the middle section of double-sided welds. It is generally visible in the center of the weld projection on the film. Since underflow significantly reduces the effective cross-sectional area, it results in a large difference in density, making it easy to detect. There is always a certain dimension in the length direction, and the image on the film remains clear. Slag inclusions are relatively easy to detect through radiographic inspection. This is because the density of non-metallic inclusions in the weld metal is low, resulting in a large difference in density contrast during radiographic inspection; similar to pores, they can be clearly reflected on the film. However, the determination of its dimension in the depth direction is not similar to that of pores; due to the irregular shape of the inclusions, there is a noticeable unevenness in darkness on the negative. In radiographic inspection, tungsten inclusions result in a distinct light-white spot image on the film, as tungsten has a higher density than the weld metal, which leads to greater attenuation of the radiation intensity. Pores: Since pores are filled with gas, they result in a reduction of radiation intensity that tends to be zero. As they represent volume defects, there is a significant difference in density, making them easy to detect on radiographic films and facilitating their evaluation. The images of pores on the film usually appear as individual ones, in chains, or in dense clusters, and can occur at any location within the weld. On the negative, these pores are characterized by a higher darkness at the center, with regular edge contours that are clearly visible.