Selecting the method of bending depends on the pipe diameter, wall thickness, material, and the required bend radius, the conditions of production, existing equipment such as pipe bending machine, accuracy and quality. Most important for high-quality flexible is the choice of ways to bend. Pipe must be bent, within certain tolerances, as the outside diameter and wall thickness. There is variation in wall thickness in longitudinal direction, and variation in wall thickness depends on the method for manufacturing the pipes. All the existing mechanisms for cold bending of pipes on machines without causing a ripple on the inside of the bend (cold smooth bending) are various structural performance. Pipe bending is accompanied by undesirable phenomena for subsequent operation. These include thinning of the wall on the outside of the bend, ovalisation (flattening) in the cross-sectional bend, ripple formation and breaks on the inside of the bend.

Furthermore, the process is complicated by the fact that, after bending a resilient resistance, which changes the radius of the bend pipe. Is also the location of the fold value along the tube. If the bend radius is small, the tube is easier to bend closer to its ends and harder in the middle part of it. At the end of the bent pipe wall thinning on the outside of the bend is less than the fold, made in the middle. Therefore, in middle of the bend radius should be chosen larger than the bending of the tube end.

When bending the pipe is cold-hardening of metal and there are residual stresses. On the inside of the bend there are plastic compressive strain. When a curved section of pipe under internal pressure will increase the radius of the bend in the compressed layers are tensile stresses act. At the same time observe the effect of Baushintera metal after plastic deformation of the compression is low tensile yield strength.