1. The causes of spiral wall thickness unevenness are: uneven wall thickness caused by the piercing machine rolling center line is not correct, the inclination angles of the two rollers are not equal, or the amount of pressure before the head is too small, which is generally distributed in a spiral shape along the entire length of the steel pipe. Uneven wall thickness caused by the premature opening of the centering roller, improper adjustment of the centering roller, and shaking of the top rod during the rolling process is generally distributed in a spiral shape along the entire length of the steel pipe.
Measures: Adjust the rolling center line of the piercing machine to make the inclination angles of the two rollers equal, and adjust the tube rolling mill according to the parameters given in the rolling table. For this situation, adjust the centering roller opening time according to the rough pipe outlet speed. Do not open the centering roller too early during the rolling process to prevent the top rod from shaking and causing uneven wall thickness. The centering roller opening needs to be appropriately adjusted according to the change in the rough pipe diameter, and the size of the rough pipe runout should be considered.

2. Causes of linear wall thickness unevenness: The height of the mandrel pre-penetration saddle is not adjusted properly. The mandrel contacts the rough tube on one side during pre-penetration, causing the rough tube to cool too fast on the contact surface, resulting in uneven wall thickness or even concave defects. The gap between the continuous rolling rollers is too small or too large. Deviation of the center line of the tube mill. Uneven pressure reduction of single and double stands will cause linear symmetrical deviations of the steel pipe in the single stand direction (extra thick) and double stand direction (extra thick). Mortar fracture and large differences in the gap between the inner and outer rollers will cause linear asymmetrical deviations in the steel pipe. Improper continuous rolling adjustment, stacking steel, and drawing steel rolling will cause linear wall thickness unevenness.
Measures: Adjust the height of the mandrel pre-penetration saddle and ensure that the mandrel is aligned with the rough tube. When changing the hole type and rolling specifications, the roller gap should be measured to keep the actual roller gap consistent with the rolling table. Use an optical centering device to adjust the rolling center line, and calibrate the center line of the tube mill during the annual overhaul. Replace the broken frame in time, measure the inner and outer roll gaps of the continuous rolling rollers, and replace them in time if there are any problems. During continuous rolling, avoid pulling and piling steel.

3. Causes of uneven wall thickness at the head and tail: The cutting inclination and curvature of the front end of the tube billet are too large, and the centering hole of the tube billet is not correct, which can easily cause uneven wall thickness at the head of the steel pipe. The elongation coefficient is too large during perforation, the roller speed is too high, and the rolling is unstable. The unstable steel throwing of the punching machine can easily cause uneven wall thickness at the tail of the rough pipe.
Measures: Check the tube billet to prevent the cutting inclination and large pressure reduction at the front end of the tube billet. The centering hole should be corrected when changing the hole type or overhauling. Use a lower perforation speed to ensure the stability of rolling and the uniformity of the rough pipe wall thickness. When the roller speed is adjusted, the matching guide plate is also adjusted accordingly. Pay attention to the use status of the guide plate and increase the inspection of the guide plate bolts to reduce the movement of the guide plate during steel rolling to ensure stable steel throwing.