Straightening of LSAW steel pipe

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 pipes, special pipes for machinery and equipment, 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 pipe, because the deviation of the straightness is directly related to the processing of threads and hoops at the pipe ends of the oil casing and transportation pipes, connection, and twisting deformation in the process of pipeline use. 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.

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, bending is the role of internal stress 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.

Internal stress is a kind of what things? Temperature, the influence of external forces and deformation of a molecular interaction force. Steel pipe in the molding, welding, will also be subject to the welding temperature, molding bending the influence of 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 process of straight seam steel pipe, the purpose is to eliminate the internal stress of the steel pipe and increase the strength of straight seam steel pipe.

The pipe to be straightened is fed into the lower roller of the straightening machine from the feeding device at the left (or right) end of the machine, and the upper roller is lowered so that it presses the pipe to the corresponding position and then stops. Upper and lower roller system were straightened with the axis of the pipe tilted at a certain angle, the rollers of the hyperbolic type bus and the outer diameter of the pipe coincides with the envelope.

The three upper rollers are pressed on the pipe under the action of their respective hydraulic cylinders, and the two lower rollers are driven to rotate by their respective hydraulic motors, driving the pipe to rotate around the axis as well as move along the axial direction. Changing the direction of rotation of the hydraulic motor can change the direction of rotation and axial movement of the pipe, realizing reversible straightening. Then the straightened pipe is sent to the material rack through the discharging device at the other end. For pipes with large local bending deformation, the punches at both ends can be used to straighten locally first and then straighten as a whole.