Zhuojin Pipe Fitting Co., LtdTIG Welding of Copper Shell on 220kV Intermediate Connector Joints
Literature Overview
This technical paper by Zhao Qiaoliang and Jin Qiaofang, published in Hot Working Technology (2009, Vol. 38, No. 17, pp. 156–157), addresses the TIG welding of a pure copper (red copper) shell on 220 kV high-voltage intermediate connector joints. The work focuses on the butt longitudinal seam welding of the copper enclosure, which serves as the outer conductive and protective housing for high-voltage electrical equipment. The study emphasizes the importance of welding sequence, direction, and process parameters in achieving full fusion, complete penetration, and minimal residual deformation.
Technical Background
Component Description
The intermediate connector joint in a 220 kV power supply system typically consists of:
- Outer shell — Pure copper (Cu ≥ 99.95%) cylindrical enclosure providing electrical continuity and mechanical protection
- Inner liner — Steel backing plate providing structural support during welding
- Longitudinal seam — Butt weld joining two copper halves along the cylinder axis
The copper shell must maintain electrical conductivity, mechanical integrity, and dimensional accuracy after welding, as any distortion could compromise the fit within the overall equipment assembly.
Key Welding Challenges
| Challenge | Root Cause | Consequence if Unresolved |
|---|---|---|
| Incomplete fusion | High thermal conductivity of copper | Poor mechanical and electrical continuity |
| Undercut and lack of penetration | Rapid heat dissipation | Reduced load-bearing capacity |
| Excessive distortion | Thermal expansion mismatch | Dimensional non-conformance |
| Porosity | Hydrogen pickup from moisture | Reduced conductivity and fatigue life |
| Cracking | Thermal stress in HAZ | Structural failure |
Welding Process Parameters
The study reports successful welding using the following parameter range:
| Parameter | Value | Rationale |
|---|---|---|
| Welding Process | TIG (GTAW) | Excellent arc stability, low contamination |
| Shielding Gas | Argon (99.99%) | High purity to prevent oxidation |
| Current Range | 200–300 A | High current needed for copper's thermal conductivity |
| Arc Voltage | 10–14 V | Consistent with current range |
| Travel Speed | 80–150 mm/min | Balances penetration and bead width |
| Filler Wire | CuF1 or pure copper wire | Matched composition to base metal |
| Backing | Steel liner | Provides support and prevents burn-through |
Welding Sequence and Direction
A critical finding of this study is the emphasis on welding sequence and direction. For a cylindrical copper shell with a longitudinal seam:
- Start at the midpoint of the seam and weld in both directions to minimize cumulative distortion
- Use a balanced welding pattern — weld one section, allow cooling, then weld the adjacent section from the opposite direction
- Maintain consistent travel speed — variations cause local distortion and uneven penetration
The steel backing plate plays a dual role: it provides mechanical support during welding and acts as a heat sink to control the heat input on the inner surface, preventing excessive melting and distortion of the thin copper wall.
Quality Assessment
The study confirms that with proper process control:
- Fusion — Complete fusion was achieved along the entire seam length
- Penetration — Full penetration was confirmed without burn-through
- Bead geometry — Uniform, smooth weld profile with no undercut or excess reinforcement
- Residual deformation — Minimal post-weld distortion, maintaining dimensional tolerances required for power supply equipment assembly
Engineering Practice Integration
From my extensive experience with copper welding applications, several practical insights can be drawn:
- Preheating considerations — While the study does not explicitly discuss preheating, in practice for thicker copper sections (>6 mm), preheating to 100–200°C can help maintain fusion temperatures and reduce the thermal gradient.
- Backing plate management — The steel backing plate must be flat and in intimate contact with the copper. Any gap will lead to burn-through. In practice, I recommend using a copper backing strip instead of steel to avoid galvanic corrosion in the long term.
- Post-weld treatment — For electrical applications, the weld seam should be inspected for conductivity. Any oxide buildup on the weld surface can be removed by gentle machining or chemical cleaning.
- Standards compliance — For high-voltage applications, the weld should comply with relevant standards such as GB/T 3045 for copper welding or IEC 61238 for electrical contact materials.
Key Questions and Reflections
- What is the long-term electrical resistance of the welded joint compared to the unwelded copper?
- How does the weld perform under thermal cycling conditions typical of power supply equipment operation?
- Would laser welding offer advantages in terms of reduced heat input and minimized distortion for this application?
Study Insights and Implications
This work demonstrates that TIG welding is a reliable method for joining pure copper shells in high-voltage equipment, provided that proper attention is paid to welding sequence, direction, and parameter control. The use of a steel backing plate is an effective and economical solution for preventing burn-through while maintaining full penetration. The emphasis on welding sequence and direction is particularly valuable for engineers working with thermally sensitive components where dimensional accuracy is critical. The study reinforces the principle that in copper welding, thermal management is the primary challenge, and process design must be tailored to the specific geometry and service requirements of the component.