CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Reverse Wire Feeding TIG Welding Application in Pressure Piping
Literature Overview
The paper by Zhao Qiaoliang from Zhejiang Industry and Trade College, published in Hot Working Technology in 2008, presents the application of reverse wire feeding (RWF) TIG welding technology in pressure piping fabrication. This technique, also known as cold wire TIG or hot wire TIG depending on the configuration, represents a significant advancement in productivity for thin-wall and medium-wall pressure pipe welding where conventional TIG welding is too slow and labor-intensive.
Core Technical Content
Reverse wire feeding TIG welding modifies the conventional TIG process by adding a separate consumable wire that is fed into the weld pool from the rear (reverse direction) of the torch. In the reverse configuration, the wire is fed through the torch body opposite to the welding direction, with the wire contact point positioned behind the arc. This arrangement allows the wire to be melted by the arc and the weld pool while the tungsten electrode remains non-consumable and provides stable arc ignition and control.
The key advantages of this technique for pressure piping applications include:
- Significantly increased deposition rate compared to pure TIG (typically 2–3 times faster)
- Reduced tungsten contamination and electrode wear
- Improved weld bead geometry with reduced undercut
- Better control of weld pool shape and penetration
- Reduced heat input compared to GMAW while maintaining TIG-quality welds
Process Parameters and Comparison
| Parameter | Conventional TIG | Reverse Wire Feeding TIG |
|---|---|---|
| Deposition rate | 0.5–1.5 kg/h | 2.0–5.0 kg/h |
| Travel speed | 40–80 mm/min | 80–200 mm/min |
| Arc current | 80–160 A | 100–200 A (arc) + 40–80 A (wire heating) |
| Heat input | 0.5–1.5 kJ/mm | 0.8–2.0 kJ/mm |
| Tungsten diameter | 2.4–3.2 mm | 2.4–3.2 mm |
| Wire diameter | N/A | 1.0–2.0 mm |
| Wire feed speed | N/A | 200–600 mm/min |
| Shielding gas | Ar or Ar/He | Ar or Ar/He |
Application in Pressure Piping
Pressure piping systems, particularly those in power plants, petrochemical facilities, and nuclear installations, require welds that meet stringent quality standards. The reverse wire feeding TIG technique offers several benefits specific to this application:
- Single-pass capability for thin-wall pipes: For pipe diameters below DN50 with wall thicknesses of 2–4 mm, the technique can achieve full penetration in a single pass, eliminating the need for multiple TIG passes.
- Reduced distortion: The lower heat input compared to MIG/MAG welding results in less angular and longitudinal distortion, which is critical for maintaining dimensional accuracy in spool piece fabrication.
- Backside protection: When combined with back-side shielding gas, the technique produces clean, smooth backside weld beads without the need for backing strips.
- Compatibility with stainless steel and alloy piping: The technique is particularly well-suited for austenitic stainless steel piping (304, 316, 321) and nickel-based alloy piping where weld quality is paramount.
Defect Analysis and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Wire misalignment | Improper wire guide setup | Regular calibration of wire feed mechanism; use of precision wire guides |
| Arc instability | Contaminated wire surface | Cleaning wire before feeding; maintaining wire storage conditions |
| Excessive penetration | Overheated wire tip | Adjusting wire feed speed; reducing wire preheat current |
| Poor fusion | Insufficient arc current | Increasing arc current; adjusting torch angle |
| Tungsten inclusion | Wire contacting tungsten | Maintaining proper wire-to-tungsten standoff distance |
Engineering Practice Implications
The adoption of reverse wire feeding TIG welding in pressure piping fabrication requires careful procedure qualification per applicable codes such as ASME Section IX or NB/T 47014. The procedure must qualify the specific combination of arc current, wire feed current, wire feed speed, travel speed, and torch angle used in production.
For critical piping applications such as nuclear Class 1 piping or high-pressure hydrocarbon service, additional considerations include:
- Hydrogen control through low-hydrogen filler metal selection and proper shielding gas management
- Interpass temperature monitoring to prevent excessive grain growth in the HAZ
- Post-weld examination requirements including 100% RT or UT for butt welds
- Qualification of the wire feed mechanism as part of the welding procedure specification
Reflections and Study Insights
The elegance of reverse wire feeding TIG welding lies in its ability to combine the weld quality advantages of TIG with improved productivity, without requiring the operator to master the more complex GMAW process. For pressure piping fabrication shops that have invested in skilled TIG welders, this technique represents a natural evolution that can significantly improve throughput while maintaining the weld quality standards required by pressure vessel and piping codes. The 2008 publication timing is notable, as it coincides with China's rapid infrastructure development period when pressure piping fabrication capacity was in high demand. This work demonstrates the practical engineering value of process innovation that builds upon existing skills rather than requiring entirely new capabilities.