What Causes Straight Seam Steel Pipes To Bend During The Production Process

The straightening of straight seam steel pipes is an important process in the production of straight seam steel pipes. Especially for API standard oil casings, oil and gas pipes, and special pipes for mechanical equipment that have higher quality requirements. These steel pipes not only have strict requirements on steel grade and weld quality but also have high requirements on the straightness of the steel pipes.

Because the deviation of straightness is directly related to the processing and connection of the pipe end threads and pipe hoops of oil casing and delivery pipes, as well as the distortion and deformation of the pipes during use. There are currently two processing forms of pipe end wire turning - pipe rotation and tool rotation. Most wire processing uses pipe rotation, which requires higher straightness of the steel pipe.

So why do steel pipes bend during the production process? There are many reasons for the bending of steel pipes, such as the thermal impact of the welding seam, eccentricity during forming, compression force, imbalance of bending force, etc. But fundamentally speaking, bending is the result of internal stress in the steel pipe. Simply put, bending is a stress imbalance. So, does a straight steel pipe have no internal stress? No. Straight steel pipes also have internal stress, but the internal stress of straight pipes is smaller.

What is internal stress? Internal stress is a term in physical mechanics. Its essence is the interaction force between molecules when the material is deformed due to the influence of temperature and external force. When steel pipes are formed and welded, they will also be affected by external forces such as welding temperature and forming bending, resulting in internal stress. The cross-section of the steel pipe is an annular shape, and two basic stresses will be generated in this annular area: a force parallel to the annular shape and a force perpendicular to the annular shape. Parallel stresses will cause the tube to become out of round; vertical stresses will cause the tube to bend. Therefore, there is a cold diameter expansion process in the production process of straight seam steel pipes. The purpose is to eliminate the internal stress of the steel pipe and increase the strength of the straight seam steel pipes.