1. The causes of spiral-shaped uneven wall thickness in steel pipes are: uneven wall thickness caused by misalignment of the piercing mill rolling centerline, unequal inclination angles of the two rolls, or insufficient pre-pressurization of the mandrel. This unevenness generally presents a spiral distribution along the entire length of the steel pipe. Uneven wall thickness caused by premature opening of the centering roll, improper adjustment of the centering roll, and mandrel vibration during rolling is also generally present in a spiral distribution along the entire length of the steel pipe.

Measures for spiral-shaped uneven wall thickness in steel pipes: Adjust the piercing mill rolling centerline to ensure equal inclination angles of the two rolls. Adjust the rolling mill according to the parameters given in the rolling schedule. For this situation, adjust the opening time of the centering roll according to the tube exit speed. During rolling, the centering roll should not open too early to prevent mandrel vibration and uneven wall thickness. The opening degree of the centering roll needs to be adjusted appropriately according to the change in tube diameter, taking into account the amount of tube runout.

2. Causes of linear uneven wall thickness in steel pipes: Improper adjustment of the mandrel pre-penetration saddle height, causing the mandrel to contact the tube on one side during pre-penetration, resulting in excessively rapid temperature drop on the contact surface, leading to uneven wall thickness or even denting defects. Insufficient or excessive gap between rolling mill rolls. Deviation of the rolling mill centerline. Uneven reduction in single and double stands, causing linear symmetrical deviations in the single-stand (overly thick) and double-stand (overly thick) directions of the steel pipe. Broken mandrels and large differences in the inner and outer roll gaps cause linear asymmetrical deviations in the steel pipe. Improper continuous rolling adjustments, such as steel stacking or pulling, can cause linear uneven wall thickness.

Measures to address linear uneven wall thickness in steel pipes: Adjust the height of the mandrel pre-penetration saddle to ensure alignment between the mandrel and the tube. Measure the roll gap when changing the roll pass and rolling specifications to ensure the actual roll gap matches the rolling schedule. Adjust the rolling centerline using an optical alignment device, and correct the rolling mill centerline during the annual overhaul. 1. Replace broken stands promptly. Measure the inner and outer roll gaps of the continuous rolling mill rolls and replace any damaged sections immediately. Avoid pulling or piling steel during continuous rolling.

3. Causes of uneven wall thickness at the head and tail of the steel pipe: Excessive slant or curvature at the billet tip, and misalignment of the billet centering hole can easily cause uneven wall thickness at the pipe head. Excessive elongation coefficient during piercing, excessively high roll speed, and unstable rolling can also lead to uneven wall thickness at the tail of the tube.

Measures to address uneven wall thickness at the head and tail of the steel pipe: Inspect the billet to prevent excessive slant or reduction at the billet tip. Correct the centering hole when changing the die type or during maintenance. Use a lower piercing speed to ensure rolling stability and uniformity of the tube wall thickness. When the roll speed is adjusted, the matching guide discs should also be adjusted accordingly. Monitor the condition of the guide discs and increase the inspection intensity of the guide disc bolts to reduce the axial movement of the guide discs during rolling and ensure stable steel ejection.