Why does the steel pipe bend in the production process

Straightening of LSAW steel pipe is an important process in the production of LSAW steel pipe. Especially for the higher quality requirements of API standard oil casing and oil and gas pipe, machinery and equipment special pipe, these kinds of steel pipe not only in the steel grade and weld quality has strict requirements, the straightness of the steel pipe also has high requirements.

Because the deviation of straightness is directly related to the oil casing and pipe end thread and pipe hoop processing, connection, and pipeline use in the process of distortion and deformation. There are two existing forms of pipe end thread turning - pipe rotation and tool rotation, and most of the thread turning process adopts pipe rotation, which requires higher straightness of the steel pipe.

So why do steel tubes get bent during the production process? There are many reasons for tube bending, such as the thermal influence of the weld for welding, eccentricity during molding, and compression force, bending force imbalance, and so on. But fundamentally, the bending is the role of internal stresses in the steel pipe, simply put, bending is the stress imbalance. So, straight steel pipe is no internal stress? No. The straight steel pipe also has internal stresses. Straight steel pipe also has internal stress, just straight pipe internal stress is smaller.

What is internal stress? Internal stress is the physical mechanics of the statement, its nature, is the material by the temperature, the external force affects the deformation of a molecular interaction force. Steel pipe in the molding, welding, but also by the welding temperature, molding bending these external forces and produce internal stress.

The cross-section of a steel pipe is an annulus, and in this annulus area there are two basic stresses: the force parallel to the annulus and the force perpendicular to the annulus. Parallel stresses will make the pipe out of round; perpendicular stresses will make the pipe bend. Therefore, there is a cold expansion process in the production of LSAW steel pipe, the purpose is to eliminate the internal stress of the steel pipe and increase the strength of LSAW steel pipe.