The classification of elbows is based on their curvature radius, which can be categorized into long-radius and short-radius elbows. Long-radius elbows refer to those with a curvature radius equal to 1.5 times the pipe's outside diameter, denoted as R = 1.5D. Short-radius elbows have a curvature radius equal to the pipe's outside diameter, represented as R = D. In this formula, D is the elbow diameter, and R is the curvature radius. When categorized by pressure class, there are approximately seventeen types, which are consistent 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 angle, there are 45° elbows, 90° elbows, and 180° elbows. This results in a wide variety of elbow types. When placing an order, the specification is often as follows: for example, "LR STD 90° 8" indicates a long-radius elbow with a pressure class of STD and an 8" bend angle; or, "SR XS 45° 4" signifies a short-radius elbow with a pressure class of XS and a 4" bend angle. The above outlines the general classification of elbows.