1) Uneven wall thickness caused by adjustment reasons such as the centerline of the piercing machine being off, unequal angles of the two rolling rolls, or too little downward pressure in front of the punch, is generally distributed in a spiral pattern along the full length of the steel pipe.

2) Uneven wall thickness caused by the early opening of centering rolls, improper adjustment of centering rolls, and shaker rod vibration during rolling, generally distributed in a spiral shape along the entire length of the Q345B seamless steel tube.

Measures:

1) Adjust the piercing machine rolling centerline to equalize the tilt angles of the two rolls, and adjust the rolling mill according to the parameters given in the rolling schedule.

2) For Case *, adjust the centering roller opening time based on the tube mill export speed. Avoid opening the centering roller too early during the rolling process to prevent rod vibration and uneven wall thickness. The centering roller opening size should be adjusted appropriately according to the change in tube diameter, considering the tube's fluctuation amount.

2. Uneven wall thickness in a straight line

Cause:

1) Inadequate height adjustment of mandrel saddle during pre-insertion leads to contact with a tube wall during mandrel pre-insertion, causing rapid temperature drop on the contact surface and resulting in uneven wall thickness of Q345B seamless steel tubes or even indentation defects.