Pipe Repair Trends — Part 3 (Welding Methods)

This part covers the principles, traits and applicability of each method family.

3. Welding-Type Repair

The general approach is to weld reinforcement metal onto defective pipe, restoring service strength. Three variants:

• Weld overlay — targets shallow single-point defects
• Weld patch — targets small-area multi-pit corrosion
• Sleeve — targets large-area corrosion

Strengths

Low cost.

Weaknesses

1. Welding on a live pipeline carries burn-through risk
2. Welding in service introduces hydrogen embrittlement / cold cracking — particularly serious on hydrogen-bearing or H₂S-bearing lines (oil & gas, refinery), where hydrogen permeation aggravates the issue
3. The welded structure forms a discrete repair, not a continuous reinforcement of the host wall — defects can re-initiate at the weld toe under fatigue
4. Heat input alters the host metallurgy near the defect, sometimes lowering its strength
5. Welding requires the line to be depressurised or shut down — heavy operational impact and revenue loss
6. Risk of human error: deviations in technique and welding cycle can cause new defects

For these reasons, welding repair is generally suitable only for planned shutdowns; for in-service repair, composite methods are strongly preferred.