A bend is a fitting that changes the direction of a pipeline. Bends can be seen at pipeline intersections, turns, and around beams. Fabricated bends possess the advantages of good flexibility, high pressure resistance, and low resistance. Hence, they are frequently used in construction.

    The primary forms of bends include: bends at various angles, U-bends, return bends (also known as P-bends), and arc bends. Bends are pipe fittings with arbitrary bending angles, utilized during bending. The bending radius of a bend is represented by "R." A larger R results in a larger curved section and a smoother bend in the pipe; when R is smaller, the curved section of the pipe is shorter and the bend is sharper.

     The distance between the centerlines of the curved ends of a return bend is called the height of the return bend, denoted as "h." A return bend is a fitting with two bending angles (usually 135°).

     A U-bend is a semi-circular fitting. The distance "d" between the centerlines of both ends of the pipe is twice the bending radius "R." A U-bend can replace two 90° elbows and is commonly used to connect two circular finned radiators.

      An arc bend is a fitting with three bending angles, with side angles typically being 135° and the middle angle usually 90°. Arc bends are used to bypass other pipelines, while arc return bends are commonly used for transporting pipelines in sanitary equipment with hot and cold water supplies.

     The size of bends is determined by the pipe diameter, bending angle, and bending radius. The bending angle is determined based on drawings and actual construction conditions. A template is then created, and the bend is fabricated according to the template. The fabricated bend will be inspected against the template to ensure compliance with requirements. A circular steel bar can be used to create the template, with a diameter of 10-14mm depending on the pipe diameter. The bending radius of bends should be determined based on pipe diameter, design requirements, and relevant regulations. It shouldn't be excessively large or small.

    A very large bending radius would not only require a significant amount of material but also occupy a large area in the curved section of the pipe, making assembly difficult. If the chosen bending radius is too small, the pipe wall behind the bend will thin due to excessive stretching, reducing its strength, and causing the inner pipe wall of the bend to be compressed, resulting in a wrinkled state.

    As a general rule, the bending radius of welded bends should be no less than 1.5 times the outer diameter of the pipe. For press-formed bends, the bending radius should not be less than the outer diameter of the pipe. For cold-formed bends, the bending radius should be no less than 4 times the outer diameter of the pipe, and for hot-formed bends, the bending radius should be no less than 3.5 times the outer diameter of the pipe.

    During bending, it is generally stipulated that the wall thinning rate of the pipe after bending should not exceed 15%. This is to ensure that the pipe's original performance is not significantly altered after bending.