裂纹产生的原因:根据实践经验,气焊焊接尺寸为38×4毫米的20号钢管时,产生裂纹的主要原因是: 1.基本金属与焊条的化学成份不同,含有害元素过多;2.对口间隙过大、过小、坡口角度过大,焊咀照顾不到,使焊缝产生应力;3.点焊时加温不够,不均匀,点焊起点与终点处点得太薄;4.仰焊起点超过管子中心和管子受热不均;5.熔池过 Crack causes: According to practical experience, gas welding welding size 38 × 4 mm 20 steel, the main reason for cracks are: 1. The basic metal and welding rod of different chemical composition, containing harmful elements too much; 2 counterpart Gap is too large, too small, the bevel angle is too large, the tip can not take care of, so that the weld stress; 3 spot welding heating is not enough, uneven, spot welding starting point and end point too thin; Yang welding starting point over the pipe center and uneven heating pipe;