If you notice irregular small ‘pits’ or ‘scars’ in non-welding areas, accompanied by signs of melting and re-solidification, be aware that this is highly likely an arc strike. An arc strike is a detrimental weld defect.
It is essentially a localized zone of structural damage constituted by a sudden, high-temperature thermal cycle—characterized by instantaneous melting followed by rapid quenching. This process alters the metallurgy of the base metal, often creating a brittle martensitic structure and microscopic cracks that can compromise the entire structural integrity of the component.
Arc Strike Definition
An arc strike is defined as unintentional arc contact with the base metal outside the designated weld area. This phenomenon triggers a violent thermal cycle, escalating from room temperature to molten steel exceeding 2,500°F before cooling to less than 500°F in mere seconds. Strictly speaking, arc strikes can also occur within the weld zone; however, as welding progresses, the subsequent weld pool overlaps and remelts the initial strike area. This process effectively incorporates the previous brittle microstructures and micro-cracks into the molten pool for recrystallization. According to AWS D1.1, any arc strike on the base metal outside the weld must be removed by grinding and undergo non-destructive testing (NDT).
In addition, some forum posts and articles have discussed these issues in detail, which can be found in the following links：https://www.reddit.com/r/Welding/comments/9joqr7/arc_strikes/
Causes of Arc Strikes
The occurrence of an arc strike is typically the result of inadvertent electrical discharge between the electrode and the workpiece. The primary causes include:
- Accidental Contact: This is the most common cause, occurring when a welder accidentally touches the base metal with a live electrode (stick, wire, or tungsten) while moving the torch or adjusting position outside the weld joint.
- Improper Striking Technique: In processes like SMAW (Stick), beginners may use an aggressive “scratch start” method. If the movement is too wide or uncontrolled, it leaves strike marks on the base metal before the arc is stabilized within the joint.
- Poor Grounding (Work Lead Connection): If the work clamp is loose or attached to a surface with rust, scale, or paint, it creates high electrical resistance. This can cause “arcing” at the connection point or elsewhere as the current seeks a path of least resistance.
- Insulation Failure: Worn or damaged insulation on the electrode holder (stinger) or welding cables can lead to accidental “shorts” if the exposed conductive part brushes against the component.
- Environmental and Spatial Constraints: Interference from the surrounding environment often leads to arc strikes. In cramped or awkward working spaces (confined spaces), a welder’s restricted range of motion or obstructed line of sight increases the risk of the electrode unintentionally bumping into the base metal.
The Impacts and Consequences of Arc Strikes
The primary concern regarding an arc strike, and what the issue ultimately boils down to, is metallurgical. In ASME code-speak, these are often referred to as “metallurgical notches.” As previously mentioned, the localized thermal cycle produces martensite or very hard bainite—microstructures that are inherently crack-prone and highly sensitive to both hydrogen embrittlement and cyclic loading. It is specifically because of this internal structural degradation that arc strikes are typically required to be removed rather than ignored.
As for the role of an arc strike as a “stress point,” this is usually a secondary concern. Unless the arc strike leaves a deep pit or considerable undercut, the geometric stress concentration it creates is typically minor. While severe surface damage can indeed act as a stress riser under axial, bending, or cyclic pressure loading, such an effect would require a fairly aggressive arc strike to become a dominant factor in structural failure.
While the metallurgical alteration is the primary threat, one cannot overlook the potential for geometric degradation. If an arc strike is aggressive enough to melt the base metal without subsequent filler deposition, it effectively reduces the material’s cross-section. This creates a localized stress riser that can lead to premature failure in load-bearing applications, independent of any metallurgical deficiencies.
The following image presents a cross-sectional view of an arc strike on a pipe. This specimen serves as an excellent case study, clearly illustrating the localized reduction in cross-sectional thickness at the point of arc contact.
Prevention and Remedy
To prevent arc strikes, strict adherence to technical discipline and proper technique is essential. Welders should always ensure the arc is initiated within the designated weld zone.When finishing a weld, the arc must be extinguished carefully to avoid ‘tail-off’ marks; in TIG, a useful ‘Wire Stop’ trick is to terminate the arc by moving it onto the filler wire rather than lifting the torch directly off the base metal.
Beyond manual technique, equipment and environment management play a crucial role. First, ensure the work lead (ground clamp) is securely attached to clean base metal to avoid stray arcing. Second, use an auto-darkening welding helmet, as its improved visibility allows for precise positioning of the electrode prior to contact. When working in unfamiliar environments, with unfamiliar equipment, or in confined spaces with an obstructed line of sight, using “strike plates” for arc initiation—then moving the arc smoothly onto the workpiece—can significantly reduce the risk of accidental contact with the base metal.
If an arc strike occurs, the remedy is not merely cosmetic. According to codes such as AWS D1.1, the affected area must be ground smooth to remove all traces of the hardened martensitic layer and any micro-cracks. Following grinding, a Non-Destructive Testing (NDT) method—typically Magnetic Particle Inspection (MT) or Liquid Penetrant Inspection (PT)—must be performed to ensure that no subsurface cracks remain.
If the grinding depth exceeds the allowable material thickness tolerance, a qualified repair welding procedure may be required to restore the component’s structural integrity.
Заключение
Why is an arc strike so detrimental? Ultimately, it represents a hidden structural threat that far exceeds its minor visual appearance. Because of the instantaneous melting and rapid quenching involved, an arc strike is essentially a “micro-trauma” to the steel’s grain structure.
To mitigate such risks, welding variables and operational discipline must be tightly controlled. This means that every aspect of the process—from the grounding setup to the explicit definitions in the Welding Procedure Specification (WPS)—must be managed to eliminate the source of these “metallurgical notches” and ensure the long-term integrity of the weldment.
Russian 
English 
Chinese 
Spanish 
German