CLADDING TECHNOLOGY SHANXI CO., LTDNon-Filler TIG Back Welding Test and Application
Literature Overview
This 1992 publication by Liu Changjiang and Li Quan from Harbin Turbine Works, published in the Welding journal, documents the development and application of non-filler TIG back welding technology for pressure vessel and turbine component fabrication. This early work represents a pioneering approach to improving welding productivity while maintaining joint quality in thick-section fabrication.
Core Technical Content
Principle of Non-Filler TIG Back Welding
Non-filler TIG back welding eliminates the need for filler metal on the back side of the weld, relying instead on the base metal to fill the weld root. This technique offers several advantages:
- Reduced material consumption and cost
- Improved root weld quality through direct base metal fusion
- Simplified welding sequence (single-sided welding possible)
- Reduced risk of contamination from filler metal
- Faster welding speed due to no wire feeding
The technique is particularly applicable to:
- Thick-section pressure vessels (10-40 mm)
- Turbine casing and rotor components
- Heat exchanger tubesheets
- Nuclear reactor components
- High-pressure piping systems
Welding Process Design
The non-filler TIG back welding process requires careful design of the front-side welding parameters to achieve full penetration:
| Parameter | Front Side | Back Side | Notes |
|---|---|---|---|
| Current Type | AC or DC | DC | AC for aluminum, DC for steel |
| Current (A) | 150-250 | 80-120 | Front side determines penetration |
| Travel Speed (cm/min) | 6-10 | 4-6 | Back side slower for quality |
| Arc Length (mm) | 3-5 | 2-3 | Shorter arc for back side |
| Shielding Gas | Ar + 2% O2 | 100% Ar | Front side with trace O2 for wetting |
| Electrode | Thoriated tungsten | Pure tungsten | Back side with finer tip |
Microstructural and Mechanical Performance
The non-filler TIG back weld produces joints with the following characteristics:
- Weld metal composition: Essentially base metal composition with minimal dilution effects
- Microstructure: Uniform phase distribution without segregation from filler metal
- Hardness profile: More uniform across the weld cross-section
- Residual stress: Lower levels due to reduced thermal input variation
- Mechanical properties: Approaching base metal properties in most cases
| Property | With Filler | Without Filler | Improvement |
|---|---|---|---|
| Tensile Strength (MPa) | 420-460 | 450-480 | 5-8% |
| Elongation (%) | 22-25 | 24-28 | 10% |
| Hardness Uniformity | ±30 HV | ±15 HV | 50% |
| Root Defect Rate (%) | 3-5 | 1-2 | 60% |
| Welding Speed (cm/min) | 6-8 | 8-12 | 30% |
Quality Control Considerations
The non-filler technique requires enhanced quality control measures:
- Visual inspection: Root weld appearance must be monitored closely
- Radiographic testing: 100% RT examination recommended for critical applications
- Ultrasonic testing: TOFD or PAUT for root defect detection
- Hardness testing: Verification of proper penetration and fusion
- Dye penetrant testing: Surface-breaking defect detection on the root
Common Defects and Solutions
| Defect | Cause | Solution |
|---|---|---|
| Incomplete penetration | Insufficient front-side heat input | Increase current, reduce speed |
| Root undercut | Excessive back-side heat | Reduce back current, improve fit-up |
| Porosity | Contamination, gas entrapment | Improve shielding, surface preparation |
| Cracking | High residual stress | Reduce heat input, preheat |
| Excessive reinforcement | Poor back-side control | Optimize back-side parameters |
Engineering Application Cases
Pressure Vessel Fabrication
In pressure vessel manufacturing, non-filler TIG back welding has been successfully applied to:
- Carbon steel vessels (GB/T 150 compliance)
- Low-alloy steel vessels (15CrMo, 12Cr1MoV)
- Stainless steel vessels (304, 316L)
- Nickel alloy lined vessels
The technique reduces welding time by 25-40% compared to conventional filler wire techniques, while maintaining or improving joint quality.
Turbine Component Fabrication
For turbine components at Harbin Turbine Works, the application includes:
- Turbine casing weld seams
- Rotor disk welds
- Blade root attachments
- Steam chest connections
The improved root quality and reduced residual stress levels contribute to improved fatigue performance in cyclic loading conditions.
Study Insights and Implications
The 1992 work by Liu Changjiang and Li Quan represents an early but significant contribution to welding productivity improvement in heavy fabrication. The key insight is that for many applications, filler metal is not essential for achieving sound weld joints, and that careful process design can compensate for the absence of filler metal.
From a modern perspective, this technology aligns with current trends toward:
- Increased welding productivity and cost reduction
- Improved joint quality through simplified processes
- Reduced material waste and environmental impact
- Enhanced consistency through parameter optimization
For contemporary engineering practice, the non-filler TIG back welding technique should be considered as a viable option for:
- Thick-section fabrication where productivity is critical
- Applications where base metal composition matching is important
- Pressure vessel fabrication where code compliance is achievable
- Repair welding where filler metal availability is limited
The technology requires careful qualification under applicable codes (ASME VIII, NB/T 47014, EN 1090), with particular attention to demonstrating consistent root weld quality and adequate mechanical properties. Future development should focus on integrating this technique with automated welding systems and advanced monitoring technologies to further improve productivity and quality consistency.