The latest knowledge on steel pipe networks and recommended practices for addressing uneven wall thickness in steel pipes is essential for maintaining product quality and production efficiency. Uneven wall thickness in steel pipes typically manifests as irregularities in the spiral wall, inconsistent thickness along the pipe, and thick or thin sections at the head and tail. These issues are often caused by improper adjustments during the continuous rolling process.
**1. Causes of Spiral Wall Thickness Variations:**
- **1)** Inconsistent wall thickness from the piercing mill, unequal roll inclination angles, or insufficient pre-rolling before the head can lead to spiral-shaped thickness variations throughout the pipe.
- **2)** Premature opening of the centering roll, misalignment of the centering roll, or jerking of the ejection pin during rolling can also cause helical thickness inconsistencies.
**Measures:**
- Adjust the piercing mill’s alignment so that both rolls have equal inclination angles and follow the rolling table parameters.
- For the second case, regulate the timing of the centering roll opening based on the capillary exit speed. Avoid opening it too early to prevent the mandrel from shaking, which may cause uneven thickness. Adjust the opening degree according to the capillary diameter and consider the rebound size of the capillary tube.
**2. Causes of Linear Wall Thickness Variations:**
- **1)** Improper adjustment of the mandrel pre-wear saddle height can cause uneven contact between the mandrel and the capillary tube, leading to temperature drops and uneven wall thickness.
- **2)** Incorrect gap settings between tandem rolls.
- **3)** Misalignment of the roller centerline.
- **4)** Unbalanced rolling between single and double racks can result in symmetric deviations in ultra-thin or super-thick areas.
- **5)** A broken safety sleeve or differences in inner and outer roll gaps can cause asymmetric wall thickness.
- **6)** Poorly adjusted continuous rolling, steel rolling, or pulling operations can also result in linear thickness inconsistencies.
**Measures:**
- Adjust the mandrel pre-wear saddle height to ensure proper alignment with the capillary tube.
- When changing hole types or specifications, measure the roll gap to ensure consistency with the rolling table.
- Use an optical centering device to align the rolling centerline, and correct the mill centerline during annual overhauls.
- Replace broken or damaged rolls promptly and measure internal and external roll gaps regularly.
- Avoid steel stacking during continuous rolling to maintain uniform thickness.
**3. Causes of Head and Tail Wall Thickness Variations:**
- **1)** A large slope at the front end of the billet or a poorly centered hole can lead to uneven thickness at the head.
- **2)** Excessive extension coefficient during piercing, high roller speed, or unstable rolling can cause uneven thickness at the end.
- **3)** Instability in the steel throwing process can also result in uneven wall thickness at the capillary end.
**Measures:**
- Check the quality of the billet and avoid excessive taper cutting. Correct the centering hole when changing hole shapes or during overhauls.
- Use a lower perforation speed to stabilize the rolling process and ensure uniform wall thickness. Adjust guide plates accordingly when changing roller speeds.
- Monitor the condition of the guide plates and increase inspection of their bolts to reduce turbulence and ensure stable steel throwing.
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