Zhuojin Pipe Fitting Co., LtdTIG Welding Arc Striking Methods and Their Engineering Implications
Literature Overview
The paper by Xu Heshui (1997), published in Welding Technology (Vol. 26, No. 4, pp. 42-43), addresses a seemingly elementary yet critically important aspect of TIG welding: arc initiation methods. Despite its brevity (two pages), this article serves as a foundational reference for welders and engineers who must select appropriate arc striking techniques based on material, joint configuration, and welding position. The author, affiliated with Nanjing Chenguang Machinery Works, draws from extensive industrial practice to categorize and evaluate the principal arc initiation approaches.
Core Technical Content
TIG welding arc initiation is classified into two fundamental categories: non-contact (high-frequency oscillation) and contact (short-circuit) methods. The non-contact method, also termed high-frequency arc striking, does not require electrode-to-workpiece contact and is compatible with both DC and AC TIG welding. The contact method, known as lift-arc or scratch-arc, involves physically touching the tungsten electrode to the workpiece before lifting to establish the arc.
| Arc Striking Method | Electrode Contact | Power Supply Compatibility | Typical Application | Key Advantage |
|---|---|---|---|---|
| High-frequency non-contact | No | DC and AC | Thin-wall pipe, stainless steel, aluminum alloy | No electrode contamination; clean weld start |
| Lift-arc (contact) | Yes | Primarily DC | Thick-section carbon steel, structural welding | Simple equipment; reliable arc establishment |
| Scratch-arc (contact) | Yes | Primarily DC | Field repair, maintenance welding | No special equipment required |
Non-Contact Arc Striking
The high-frequency method employs an HF oscillator (typically 100-300 kHz) superimposed on the welding circuit to ionize the gap between the tungsten electrode tip and the workpiece surface. This method is particularly advantageous for:
- Welding reactive metals such as titanium, zirconium, and stainless steels where electrode contamination must be avoided
- AC TIG welding of aluminum and magnesium alloys where the HF provides consistent arc polarity reversal initiation
- Thin-wall piping applications where a clean, pinpoint arc start is essential for maintaining root penetration quality
Lift-Arc Method
The lift-arc technique involves a controlled mechanical lift of the tungsten electrode after brief contact with the workpiece. The author emphasizes that this method is suitable for DC TIG welding and is commonly employed in automated and semi-automated TIG systems. The controlled lift height (typically 2-4 mm) ensures stable arc establishment without electrode contamination. However, the author notes that repeated contact can cause tungsten tip erosion and workpiece surface contamination, particularly problematic for high-purity applications.
Engineering Practice Considerations
From a quality control perspective, arc initiation method selection directly impacts the following weld quality parameters:
- Arc stability at weld start — The first 5-10 mm of weld bead is most susceptible to defects including undercut, incomplete fusion, and excessive spatter
- Electrode contamination — Contact methods risk tungsten inclusion in the weld metal, particularly critical for stainless steel and nickel-based alloy welding
- Automation compatibility — Lift-arc systems integrate seamlessly with CNC-controlled TIG welding stations for pipe and fitting manufacturing
- Safety considerations — High-frequency equipment requires proper shielding and grounding to prevent RF interference with nearby instrumentation
Common Defects Related to Arc Striking
| Defect Type | Primary Cause | Countermeasure |
|---|---|---|
| Tungsten inclusion | Contact arc striking without electrode cleaning | Use high-frequency method; clean electrode tip after each contact |
| Porosity at weld start | Inadequate shielding gas coverage during arc initiation | Pre-flow shielding gas for 3-5 seconds before arc strike |
| Excessive undercut | Unstable arc during first pass initiation | Optimize electrode angle and travel speed at start point |
| Surface contamination | Arc contact on sensitive alloys | Employ non-contact method exclusively |
Study Insights and Reflections
Having reviewed this literature after decades of practice, I find that the seemingly simple topic of arc initiation carries profound implications for weld quality in pipe and fitting fabrication. In my experience with stainless steel piping systems and nickel-based alloy applications, the selection of arc striking method is often overlooked during WPS development yet proves critical during production quality audits. The 1997 publication, while technically straightforward, captures essential knowledge that remains directly applicable to modern TIG welding practice, particularly in the context of orbital TIG welding for pipe joints where consistent arc initiation is automated but must be properly configured.
The paper's emphasis on the compatibility matrix between arc striking methods and power supply types (DC versus AC) is particularly relevant today as inverter-based TIG power sources have become standard equipment. Modern inverters integrate high-frequency oscillation circuitry as standard, making non-contact arc striking the default for most applications. Nevertheless, understanding the underlying physics and limitations of each method remains essential for troubleshooting arc instability issues in production environments. Engineers involved in welding procedure qualification should explicitly document the arc initiation method in the WPS, as this parameter can significantly influence the reproducibility of qualified welds across different production shifts and operators.