Straightening is an important process in the production of LSAW steel pipes. Especially for oil casing and oil and gas pipes of API standard with high quality requirements, special pipes for machinery and equipment.These kinds of steel pipes not only have strict requirements on the 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 thread and pipe hoop of the oil casing and conveying pipe, as well as the distortion and deformation during the use of the pipeline. There are two processing forms of pipe end threading – pipe rotation and tool rotation. Most of the threading processing adopts the method of pipe rotation, which requires higher straightness of the steel pipe.
Affected by the internal stress of the steel pipe, the thermal influence of the welding seam, the eccentricity during forming, the tightening pressure, and the unbalance of the bending force will cause the bending of the LSAW steel pipe.
Internal stress refers to the stress that remains inside the object after the external load is removed. It is caused by the uneven volume change of the macroscopic or microscopic organization inside the material. The cold expansion process in the production process of LSAW steel pipe is to eliminate the internal stress of the steel pipe
Steel pipe straightening adjustment principle:
1. The pipe is bent in the same direction as the weld
Reason: The normalizing of the weld is not sufficient, and there is thermal stress on the side of the pipe near the weld, so it bends in one direction after cooling.
Solution:a. Adjust the intermediate roller to appropriately increase the deflection curve;
b. Secondary straightening;
c. When it is impossible to straighten directly, the pipe is tempered as a whole.
2. The tube is irregularly bent
Reasons: a. The pressure between the three rollers is inconsistent;
b. The straightening roller wears a lot
Solution: Check and adjust whether the upper straightening roller is loose, and use a sample rod to straighten the length of the contact line between the three tracks.
3. The length of the tube is shortened greatly
Reason: The difference between the rolling angles of the three straightening rollers is too large; the straightening pressure is large.
Solution: a. Adjust the rolling angle to be as consistent as possible;
b. Properly adjust the straightening pressure.
4. One end of the tube is bent
Reason: The distance between the rollers is too large.
Solution: choose a straightening machine with a smaller spacing suitable for the corresponding pipe diameter.
5. The head of the tube is not round
Reason: The contact phases between the three straightening lights are improperly distributed or overlapped, and the roller pressure is too high.
Solution: Adjust the angle between the light and the limit appropriately, and adjust the pressure of the roller on the tube.