The classification of elbows is based on their curvature radius, which can be categorized into long-radius elbows and short-radius elbows. Long-radius elbows refer to those with a curvature radius equal to 1.5 times the pipe's outer diameter, denoted as R = 1.5D. Short-radius elbows have a curvature radius equal to the pipe's outer diameter, indicated as R = D. In this formula, D is the elbow diameter, and R is the curvature radius. In terms of pressure ratings, there are approximately seventeen types, which are the same as 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-degree elbows, 90-degree elbows, and 180-degree elbows. This results in a wide variety of elbow types. When placing an order, the order often specifies the type as follows: for example, "LR STD 90o 8" indicates a long-radius elbow with a STD pressure rating, a 90-degree angle, and an 8" diameter; or "SR XS 45o 4" denotes a short-radius elbow with an XS pressure rating, a 45-degree angle, and a 4" diameter. The above provides an overview of elbow classifications.