Zhuojin Pipe Fitting Co., LtdArc Striking Methods in TIG Welding
Overview of the Literature
This 1997 paper by Xu Heshui from Nanjing Chengchuan Machine Factory, published in Welding Technology, addresses a fundamental but often overlooked aspect of TIG (GTAW) welding: the arc striking method. The paper is concise (two pages) but covers a topic that directly affects weld quality, equipment longevity, and operator safety. For engineers working with pipeline fabrication, pressure vessel manufacturing, and pipe fitting production, understanding arc initiation is not merely academic — it is a practical requirement for achieving repeatable, defect-free welds in production environments.
Classification of Arc Striking Methods
The paper categorizes TIG arc striking into two principal families: non-contact methods and contact (short-circuit) methods. The following table summarizes the key characteristics of each approach.
| Method | Contact with Workpiece | Suitable for DC | Suitable for AC | Typical Application |
|---|---|---|---|---|
| High-frequency oscillation arc striking | No | Yes | Yes | Automation, stainless steel, thin-wall pipes |
| Pulse high-frequency arc striking | No | Yes | Yes | Precision welding, aerospace components |
| Lift (contact) arc striking | Yes | Yes | Yes | Manual welding, field repair, thick sections |
| Scratch (contact) arc striking | Yes | Yes | Limited | Legacy practice, not recommended for modern applications |
Non-Contact Arc Striking
The non-contact method employs high-frequency voltage (typically 100–300 kHz) applied between the tungsten electrode and the workpiece to ionize the shielding gas and establish an arc without physical contact. This is the preferred method for automated TIG welding stations and robotic welding cells. The paper notes that this method is equally effective for both DC and AC TIG welding, making it universally applicable across the full range of materials — from carbon steel pipes to aluminum pipe fittings and stainless steel flanges.
A critical engineering consideration is the high-frequency interference with nearby electronic equipment. In modern fabrication shops equipped with digital control systems, PAUT or TOFD inspection instruments, or automated seam tracking devices, the high-frequency arc starter can induce electromagnetic interference. Engineers must specify adequate shielding and grounding for control electronics, or alternatively employ pulsed high-frequency arc starters that reduce the interference envelope.
Contact (Lift) Arc Striking
The contact method, commonly called "lift arc," involves touching the tungsten electrode to the workpiece and then lifting it to a set distance. The momentary short circuit creates a low-resistance path, and upon separation, the arc is established. This method is widely used in manual TIG welding of pipe joints, particularly in the field repair of pipelines and in the fabrication of pipe fittings where automated equipment is not available.
The paper highlights an important practical point: the lift arc method requires precise control of the electrode-to-workpiece distance. If the electrode is lifted too quickly, the arc may fail to strike or may be unstable. If lifted too slowly, the tungsten tip can pick up base metal contamination, leading to tungsten inclusion defects in the weld. For pipe welding applications, where the joint geometry may be constrained (e.g., in-situ welding of large-diameter pipe spools), the lift arc method offers flexibility that non-contact methods cannot always provide.
Engineering Practice Implications
In my experience with pipeline fabrication and pipe fitting production, the choice of arc striking method has measurable effects on weld quality. The following observations are drawn from field experience:
- Tungsten contamination from improper lift arc striking is a leading cause of weld defects in field-welded pipe joints, particularly where operators lack consistent training.
- Automated TIG welding of ERW pipe seam repair and stainless steel pipe welding stations universally employ high-frequency non-contact arc striking, and the reliability of the arc starter directly impacts production throughput.
- For AC TIG welding of aluminum pipe fittings, the high-frequency arc starter must be properly synchronized with the AC waveform to ensure reliable arc initiation on each half-cycle.
A practical recommendation derived from this literature is to standardize arc striking procedures in welding procedure specifications (WPS). The WPS should explicitly state the arc striking method, the electrode preparation requirements, and the acceptable electrode-to-workpiece distance for lift arc applications. This reduces operator variability and improves first-pass weld quality.
Key Reflections
This short paper, while dated, addresses a topic that remains relevant in current practice. The fundamental physics of arc initiation has not changed, and the practical challenges — tungsten contamination, arc stability, and interference with instrumentation — persist in modern fabrication environments. Engineers should not overlook the arc striking method as a minor procedural detail; it is a critical process parameter that influences weld integrity, particularly in applications governed by strict codes such as ASME B31.3 or API 5L.