Causes of Diameter Deviation in Spiral Submerged Arc Welded Pipe During Coil Forming

In the production process of spiral submerged arc welded pipes (SSAW pipes), diameter deviation is one of the most common forming defects. This issue can lead to quality problems, affecting the structural integrity and performance of the pipes. Below, we analyze the key causes of diameter deviation in spiral submerged arc welded steel pipes and provide insights into how to prevent them.

1. "Crescent Bend" in Steel Strip

The "crescent bend" (uneven curvature) in the steel strip is a major factor causing diameter deviation. During production, if the forming angle remains unchanged, the only way to compensate for this bend is by introducing misalignment, which can result in diameter deviations.

2. Improper Process Parameters

If the deformation between the feeding edge and the free edge is uneven due to incorrect process settings, excessive differences can lead to misalignment and diameter deviations.

3. Over-Tight Seam Biting

If the steel strip deviates during forming, the entry angle at the forming machine increases, causing the rear bridge angle to expand. This leads to excessive seam biting, resulting in misalignment and diameter issues.

4. Incorrect Positioning of Welding Backup Rollers

The welding backup rollers are typically offset by 10–15 mm from the #1 forming roller. If the offset is too small, it can cause positive misalignment; if too large, negative misalignment—both leading to diameter deviations.

5. Welding Deviation (Weld Off-Center)

Severe long-distance welding deviation can cause misalignment or seam separation, directly affecting pipe diameter consistency. Proper welding alignment control is essential.

6. Poor Steel Strip Feeding

Irregular feeding can cause strip deviation, leading to edge thickening and misalignment, which contributes to diameter deviation.

7. Uneven Strip Width or Poor Edge Condition

Variations in strip width or damaged edges can easily cause misalignment, leading to diameter inconsistencies.

8. Surface Irregularities in Steel Strip

Large waves, hard bends, or uneven surfaces increase the risk of misalignment. Improving leveling effectiveness is crucial to minimize these defects.

9. Improper Pre-Bending Roller Shape or Insufficient Edge Pre-Bending

If the pre-bending rollers are not properly shaped or the pre-bending amount is incorrect, misalignment and diameter deviations can occur. Adjusting pre-bending parameters is necessary for optimal forming.

Conclusion: How to Minimize Diameter Deviation in SSAW Pipes

To effectively control diameter deviation and misalignment in spiral submerged arc welded pipes, manufacturers must:

· Reduce the "crescent bend" in steel strips.

· Ensure high-quality strip jointing.

· Optimize strip feeding mechanisms.

· Avoid manual handling that may introduce bends.

· Adjust welding and forming parameters precisely.

By addressing these factors, manufacturers can improve the dimensional accuracy and overall quality of spiral submerged arc welded steel pipes, ensuring compliance with industry standards.