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Transverse cracks in LSAW (Longitudinal Submerged Arc Welded) steel pipes can compromise structural integrity and product reliability. Addressing these defects through systematic rework procedures is crucial to maintaining product standards and preventing long-term issues. Below is a detailed, step-by-step guide for managing and repairing transverse cracks effectively:
1. Confirm Defect
Conduct 100% Ultrasonic Testing (UT) for all welds.
Mark the crack's location, length, depth, and direction.
If the defect spans the entire weld, dig out and replace the entire weld using submerged arc welding. For localized defects, repair with Shielded Metal Arc Welding (SMAW).
2. Planing and Preheating
Preheat the affected area to 110–170°C.
Ensure the preheating range extends at least 150mm on both sides of the detected defect and covers a 500mm radius around the defect.
3. Gouging
Remove the defective material by gouging both ends of the crack, ensuring the weld integrity extends at least 50mm beyond the crack.
Perform gouging gently to create a smooth transition at the ends and maintain an angle greater than 45°between the transition surface and the vertical line.
Use a carbon rod angle of 60°or less, particularly reducing the angle in the crack area.
4. Polishing
Polish the gouged area to remove any blackened surface and ensure a smooth transition without sharp pits or irregularities.
5. Penetrant Testing (PT)
Once the surface has cooled to an appropriate temperature, perform PT to detect surface-breaking cracks.
6. Further Grinding
Based on PT results, grind the area further to eliminate all visible red lines indicating defects.
7. Magnetic Particle Testing (MT)
Conduct MT to confirm the absence of residual cracks.
If any cracks remain, continue grinding until MT confirms a defect-free surface.
8. Reheat Before Welding
Preheat the area again to 110–170°C, ensuring the preheat zone extends at least 150mm on both sides of the weld and covers a 500mm radius.
9. Welding
Perform welding according to standard instructions, ensuring bead width does not exceed 15mm.
Use SMAW or automatic submerged arc welding, as appropriate.
10. Post-Welding Insulation and Slow Cooling
After welding, insulate the weld with a ceramic blanket to retain heat and cool the area gradually.
11. Post-Weld Heat Treatment (PWHT)
Perform PWHT to diffuse hydrogen, relieve residual stress, and enhance weld integrity.
Recommended procedure: Heat the weld to 200°C immediately after welding, insulate with a ceramic blanket, and allow it to cool slowly over two hours.
12. Final Inspection
After 48 hours, conduct Non-Destructive Testing (NDT) to verify that the repair meets quality standards.
Conclusion
This structured approach ensures that transverse cracks in LSAW steel pipes are effectively repaired, restoring the weld's integrity and minimizing the risk of future failures. Adopting these measures enhances product reliability, reduces costs associated with defective products, and supports continuous quality improvement.
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