2) the surface quality of welding joint should be in accord with following regulations:a) There should be no cracks on weld seam surface and on heat-effected zone,there should be no defects such as slag-in and air pore on weld seamsurface.b )the depth of under cut is less than 0.5mnrthe continuous length is less than100mm.a nd ratio of total length of one weld seam on both sides is less than 10%3) .the visual and dimensional required precision should be in accord with followingregulations after the installation of gas distributing device :circular degree of cone hopper : ±5height of cone hopper: ±5smoothness of upper and lower end of cone hopper: