Bend classification is based on its radius of curvature, which can be categorized into long-radius and short-radius bends. A long-radius bend refers to one where the radius of curvature is 1.5 times the pipe's outside diameter, denoted as R = 1.5D. A short-radius bend has a radius of curvature equal to the pipe's outside diameter, R = D. In the formula, D represents the bend diameter, and R is the radius of curvature. In terms of pressure ratings, there are approximately seventeen types, which align with American pipe standards, including: Sch5s, Sch10s, Sch10, Sch20, Sch30, Sch40s, STD, Sch40, Sch60, Sch80s, XS; Sch80, Sch100, Sch120, Sch140, Sch160, XXS, with STD and XS being commonly used. By bend angle, there are 45° bends, 90° bends, and 180° bends. This results in a variety of bend types. When placing an order, the order form often specifies the following: for example, "LR STD 90o 8" indicates a long-radius bend with a STD pressure rating and an 8" 90° bend; or, "SR XS 45o 4" indicates a short-radius bend with an XS pressure rating and a 4" 45° bend. The above outlines the general classification of bends.