I. Repairable Defects (Surface-level and not affecting structural integrity)
1. Scratches, abrasions, minor folds: For shallow scratches (generally <30μm), localized grinding with an angle grinder or belt sander can smooth the surface. The wall thickness after grinding must not be lower than the minimum allowable value (usually not exceeding a negative deviation of 10%).
2. Outer folds, hairline cracks, and scars (shallow layer): If not penetrating the substrate, the abnormal layer can be removed by turning or polishing. After repair, eddy current testing or magnetic particle testing is required to confirm the absence of residual cracks.
3. Localized pits and rough surfaces: If not penetrating the pipe wall and not affecting strength, they can be ground smooth. For decorative applications, sandblasting combined with a coating can be used to conceal the defects.
4. Damaged thread ends (rotten teeth): Minor damage at the starting point can be repaired by re-tapping or rolling. For high-requirement applications, it is recommended to use wire thread inserts to reinforce the connection. ✅ All repairs must be carried out in accordance with process specifications, and ultrasonic testing, hydrostatic testing, and dimensional verification must be performed after repair to ensure safety and reliability.
II. Irreversible Defects (Involving Internal Organization or Structural Damage)
1. Internal folds, delamination, inclusions, porosity: These are internal organizational defects caused by poor billet quality or improper piercing process. They cannot be eliminated through surface treatment and the entire tube must be scrapped.
2. Through-the-wall cracks: These have penetrated the tube wall. Welding repair will introduce new stress sources, posing an extremely high risk of leakage. Repair and use are strictly prohibited.
3. Severe wall thickness unevenness, bulges: These are caused by uncontrolled rolling and cannot be corrected. They are irreversible geometric defects and pose an explosion hazard.
4. Deep scratches (>30μm): These are prone to developing into fatigue cracks under alternating loads. They are considered high-risk defects, especially in high-pressure systems, and replacement is recommended.
