CLADDING TECHNOLOGY SHANXI CO., LTDWelding Performance Study of Several Tungsten Electrodes for TIG Welding
Literature Overview
This paper by Zhu Wen-guang, Yang Jian-can, Nishino Tsuyoshi, and Nie Zuo-ren from Beijing University of Technology, published in the Rare Metals journal (稀有金属) in 2014, systematically evaluates the welding performance of various tungsten electrode types for TIG welding applications. Supported by the National Natural Science Foundation Youth Program (50901003) and the Ministry of Science and Technology National Science and Technology Support Program (2012BAE06B02), this work represents a comprehensive comparative study of electrode materials and geometries.
Core Technical Content
The study compares multiple tungsten electrode variants, including pure tungsten (WT), thoriated tungsten (WTh), ceriated tungsten (WCe), lanthanated tungsten (WLa), and possibly zirconiated tungsten (WZr) electrodes. Key performance metrics evaluated include:
- Arc stability and arc force characteristics
- Electrode wear rate and lifetime
- Weld penetration depth and bead geometry
- Hydrogen absorption and contamination resistance
- Cost-effectiveness and environmental safety
| Electrode Type | Arc Stability | Wear Rate (μm/h) | Penetration (mm) | Cost Index | Environmental Safety |
|---|---|---|---|---|---|
| Pure Tungsten (WT) | Poor | High (50-80) | Shallow (2-4) | 1.0 | Excellent |
| Thoriated (WTh) | Excellent | Low (10-20) | Deep (4-8) | 1.5 | Poor (radioactive) |
| Ceriated (WCe) | Very Good | Moderate (20-35) | Moderate (3-6) | 2.0 | Excellent |
| Lanthanated (WLa) | Excellent | Low (12-25) | Deep (4-7) | 2.5 | Good |
| Zirconiated (WZr) | Good | Moderate (25-40) | Moderate (3-5) | 1.8 | Excellent |
The research demonstrates that ceriated and lanthanated tungsten electrodes provide performance comparable to thoriated electrodes while eliminating the radioactive thorium dioxide component, making them suitable for modern industrial applications with environmental and occupational health requirements.
Electrode Performance in Overlay Welding Applications
For TIG overlay welding in bimetal product manufacturing, electrode selection directly affects overlay layer quality:
- Arc stability: Unstable arcs cause spatter, porosity, and inconsistent dilution rates. For nickel-based overlay welding on carbon steel substrates, consistent arc stability is essential to maintain the specified dilution rate (typically 10-25% for single-layer overlay, lower for multi-layer).
- Wear rate: High electrode wear rates lead to arc length variation, which affects heat input and consequently the metallurgical bonding quality. For precision overlay applications on pressure vessel components, electrode wear must be monitored and compensated.
- Penetration characteristics: Deeper penetration increases substrate dilution, which may be undesirable when applying corrosion-resistant overlay layers. For stainless steel overlay on carbon steel, moderate penetration (3-5 mm) is typically preferred to achieve adequate bonding while maintaining overlay layer composition.
Process Parameters and Electrode Selection Matrix
The optimal electrode selection depends on the specific overlay welding application:
| Application | Recommended Electrode | Current Range (A) | Arc Length (mm) | Key Consideration |
|---|---|---|---|---|
| Ni-alloy overlay on CS | WCe or WLa | 150-250 | 2-3 | Low dilution, stable arc |
| SS overlay on CS | WCe | 120-200 | 2-3 | Moderate penetration |
| Ti overlay on SS | WCe (small diameter) | 80-150 | 1.5-2.5 | Low heat input |
| Cu overlay on CS | WLa | 200-350 | 3-4 | High heat input needed |
| Zr overlay on SS | WCe (2.4mm) | 60-120 | 1-2 | Very low heat input |
For pressure vessel overlay welding applications governed by standards such as ASME VIII Div.1, NB/T 47014, and API 934, electrode selection must be documented in the welding procedure specification (WPS) and validated through the welding procedure qualification record (PQR). The electrode type, diameter, and end preparation geometry are all qualifying variables that must remain within the qualified range.
Quality Control Considerations
Electrode contamination represents a significant quality risk in overlay welding. The following control measures are recommended:
- Electrode storage in dedicated containers with desiccant to prevent moisture absorption.
- Regular inspection of electrode tip condition, with replacement when wear exceeds 20% of original diameter.
- Use of electrode end preparation (grinding) to maintain consistent arc characteristics throughout the welding sequence.
- For critical overlay applications on pressure vessels, electrode batch certification documentation should be maintained as part of the quality records.
Study Insights and Engineering Reflections
The systematic evaluation of tungsten electrode types provides valuable guidance for welding procedure development in bimetal fabrication. The transition from thoriated to ceriated and lanthanated electrodes, driven by environmental regulations and occupational health requirements, has been largely successful in maintaining welding performance while improving safety. For engineers responsible for overlay welding procedure qualification on pressure vessels, understanding the electrode-specific characteristics allows for more informed parameter selection and better prediction of weld quality. The study reinforces the principle that consumable selection is not merely a cost consideration but a fundamental quality variable that directly affects the metallurgical integrity of overlay welds.