Welded elbow according to its radius of curvature can be divided into long and short radius bend radius butt welded elbow. Radius of curvature of long radius elbow welded is 1.5 times the pipe diameter, i.e. R = 1.5D. Short radius of curvature equal to the radius of the pipe diameter welded elbow, namely R = 1D. Formula D is welded elbow diameter, R is the radius of curvature. If no special instructions, generally used in the 1.5D elbow. Large diameter elbow generally refers to more than DN600 caliber, large caliber, including large-diameter straight seam elbow elbow, elbow welded large diameter seamless elbow. Most used on the market is welded elbow, straight seam and seamless in terms of large-caliber technical equipment in addition to the raw materials, then there are expensive. Large diameter elbow angle can be divided according to a large-caliber elbow 45 degrees, 90 degrees and 180 degrees of large diameter elbow and other large-caliber elbow bend at different angles. According to the material can be divided into large diameter carbon steel elbow, elbow large diameter stainless steel, alloy steel large diameter elbow. According to the radius of curvature can be divided into long and short radius bend radius of large diameter large diameter elbow. Large diameter elbow main criteria GB, electricity standard, Sinopec standard, marine standard, Japanese standard, American standard and so on. Large diameter elbow with a smooth wall, heat medium flow resistance is small, acid, long life, easy installation.