Wall Thickness Accuracy and Straightening Method of Straight Seam Steel Pipe

The control of the wall thickness of the straight seam steel pipe is a difficult point in the production of steel pipes. At present, the methods of straight seam steel pipe manufacturers in the production of wall thickness accuracy generally include:

1. Tube billet heating

Heating should be uniform, avoiding rapid temperature rise and fall. The temperature of each rise and fall should be kept stable and slow, and the maximum rise and fall temperature should not exceed 30°C.

2. Rolling mandrel

Thick-walled pipes and solid billets with uniform wall thickness greatly reduce the probability of mandrel bending deformation, which can effectively improve the wall thickness accuracy of steel pipes.

3. The precision of mandrel

The external processing accuracy of the mandrel is controlled at ±0.1mm, and the straightness direction of the mandrel does not exceed 5mm. When welding, a precision-machined pin is inserted between the two core rods for positioning, to avoid excessive deviation of the total straightness formed by welding.

4. Process

Determine whether the centering roller is installed in place, adjust the center of the core-holding roller, the opening angle, and the opening size of each movement to be consistent, and the center of the core-holding roller should be on the rolling line

5. Centering roller

process, prevent center thinning and wall thickness increase beyond the control limit, and improve wall thickness accuracy.

6. Perforated ejector pin

The perforated ejector generally chooses a thick-walled pipe with an outer diameter of Φ108mm-Φ114mm, a wall thickness of ≥25mm, and an average wall thickness.

7. Rolling middle line

Make sure that the rolling middle line of the piercing machine is consistent with the middle line of the piercing trolley, and avoid "upper rolling" or "lower rolling" so that the tube blank is kept uniform in force during piercing.

8. Rolling things

The worn-out plugs, guide plates, rolls, and other rolling tools should be replaced in time.

9. Rolling tool device

The middle of the roll distance and guide distance must be on the rolling line. Ensure that the middle line of the guide distance and the roll distance are on the middle line of the piercing and rolling, that is, the upper and lower roller distances are equal, and the left and right guide distances are equal.

Straight seam steel pipe straightening method:

1. The straight seam steel pipe is bent in the same direction as the weld

Reason: Insufficient normalizing treatment of the weld seam, thermal stress exists on the side of the pipe near the weld seam, so it bends in one direction after cooling.

Solutions: 1. Adjust the middle roller to increase the deflection curve appropriately; 2. Straighten twice; 3. When the straightening cannot be done directly, temper the pipe as a whole.

2. Straight seam steel pipe is bent irregularly

Reasons: 1. The pressure between the three rollers is inconsistent; 2. The straightening rollers are more worn.

Solution: Check and adjust whether the upper straightening roller is loose, and use a sample stick to straighten the length of the contact line between the three lines.

3. The length of the straight seam steel pipe is greatly shortened

Reason: The rolling angle difference between the three straightening rollers is too large; the straightening pressure is relatively large.

Solution: Adjust the roller pressure angle to be as consistent as possible; properly adjust the straightening pressure.

4. One end of the straight seam steel pipe is bent

Cause: 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 straight seam steel pipe is not round

Reason: The contact phase between the three straightening rollers is improperly distributed or overlapped, and the roller pressure is too large.

Solution: Properly adjust the angle between the rollers and adjust the pressure of the rollers on the pipe.