Controlling the wall thickness of straight seam steel pipes is a challenge in steel pipe production. Currently, straight seam steel pipe manufacturers generally use the following methods to ensure wall thickness accuracy during production:
1. Billet Heating: Heating should be uniform, avoiding rapid temperature fluctuations. Each temperature increase or decrease should be stable and gradual, with the maximum temperature fluctuation not exceeding 30℃.
2. Rolling Mill Mandrel: Thick-walled steel pipes with uniform wall thickness and solid billets significantly reduce the probability of mandrel bending and deformation, effectively improving the wall thickness accuracy of the steel pipe.
3. Mandrel Accuracy: The external machining accuracy of the mandrel is controlled within ±0.1mm, and the straightness deviation of the mandrel should not exceed 5mm. During welding, a precision-machined pin is inserted between two mandrel sections for positioning to prevent excessive overall straightness deviation caused by welding.
4. Process: Ensure the centering roller device is in place, adjust the centering and opening angles of the relevant core rollers, and ensure the opening size of each action is consistent. The center of the core roller must be on the rolling line.
5. Centering Roller: The process prevents center thinning and wall thickness increase exceeding control limits, improving wall thickness accuracy.
6. Piercing Manipulator: Piercing manipulators are generally selected from thick-walled steel pipes with an outer diameter of Φ108mm-Φ114mm and a wall thickness requirement of ≥25mm with uniform wall thickness.
7. Rolling Centerline: Ensure the rolling centerline of the piercing mill is aligned with the centerline of the piercing carriage to prevent “upward rolling” or “downward rolling,” ensuring even stress on the billet during piercing.
8. Rolling Tools: Replace worn manipulators, guide plates, rolls, and other rolling tools promptly.
9. Rolling Tool Installation: The center of the roll gap and guide distance must be on the rolling line. The center line of the guide distance and roll distance of the pipe is on the center line of the piercing rolling, that is, the upper and lower roll distances are equal, and the left and right guide distances are equal.
Straightening methods for straight seam steel pipes:
(1) Straight seam steel pipe bends in the same direction as the weld.
Cause: Insufficient normalizing treatment of the weld, thermal stress exists on the side of the steel pipe near the weld, thus causing bending in one direction after cooling.
Solutions: 1. Adjust the intermediate roll to appropriately increase the deflection curve; 2. Straighten twice; 3. If direct straightening is not possible, temper the entire steel pipe.
(2) Irregular bending of straight seam steel pipe.
Causes: 1. Inconsistent pressure between the three rolls; 2. Excessive wear of the straightening rolls.
Solutions: Check and adjust whether the upper straightening roll is loose, and use a template to straighten the contact line length between the three rolls.
(3) Significant shortening of the length of straight seam steel pipe.
Causes: The difference in roll pressure angle between the three straightening rolls is too large; the straightening pressure is too high.
Solutions: Adjust the roll pressure angle to be as consistent as possible; adjust the straightening pressure appropriately.
(4) One end of the straight seam steel pipe is bent.
Cause: The distance between the rollers is too large.
Solution: Select a straightening machine with a smaller distance suitable for the corresponding pipe diameter.
(5) The head of the straight seam steel pipe is not round.
Cause: The contact phase distribution between the three straightening rollers is improper or overlaps, and the roller pressure is too large.
Solution: Adjust the angle between the rollers appropriately and adjust the pressure of the rollers on the steel pipe.
Post time: Dec-04-2025