I. Common Repair Methods and Applicable Scenarios
1. Local Grinding and Finishing: For shallow mechanical damage such as scratches, abrasions, and minor folds, use an angle grinder or belt sander to grind away sharp edges and smooth the surface. The grinding depth should not exceed 10% of the negative wall thickness deviation to avoid weakening the load-bearing capacity.
2. Turning or Polishing: Applicable to surface abnormalities that do not penetrate the substrate, such as external folds, hairline cracks, and shallow scabs. The defect layer is removed by machining, often used for structural tubes with low precision requirements. After repair, eddy current testing or magnetic particle testing is required to confirm the absence of residual cracks.
3. Thread End Repair: For thread defects at connection points, re-tapping, rolling repair, or installation of wire thread inserts (such as Helicoil) can restore connection strength, especially suitable for high-requirement flange or joint connections.
4. Sandblasting + Coating Treatment For localized pits, rough surfaces, and other point-like defects that do not affect strength, if the application is decorative or non-pressure-bearing, sandblasting can be used to unify the surface condition, followed by the application of anti-rust paint, galvanizing, or other coatings for aesthetics and protection.
II. Post-Repair Verification Requirements All repair operations must be performed using the following testing methods to ensure safety:
1. Non-destructive Testing: The repaired area must be subjected to ultrasonic testing (UT) or eddy current testing (ET) again to eliminate new cracks.
2. Hydrostatic Test: Pressure must be maintained at 1.5 times the working pressure for at least 10 seconds; no leakage is considered acceptable.
3. Dimensional Verification: The outer diameter and wall thickness of the repaired area must be measured to ensure compliance with the design minimum allowance.
