Arc strike is a weld defect that occurs when an electric arc unintentionally strikes the surface of the base metal or nearby areas during welding operations. This phenomenon can lead to localized heating, melting, and surface damage, resulting in the formation of irregularities, such as cracks, pits, or surface contamination. While arc strikes may not always directly affect the integrity of the weld joint, they can compromise the surface quality, aesthetics, and potentially the corrosion resistance of the welded component.
Example: Welding of Pressure Vessels
Let’s consider the welding of pressure vessels used in industrial applications. Pressure vessels are critical components designed to contain fluids or gases under pressure, commonly found in industries such as oil and gas, chemical processing, and power generation.
Arc Strike Weld Defect:
During the welding of pressure vessels, arc strikes can occur if proper welding procedures are not followed or if there are issues with electrode manipulation or workpiece handling. This defect manifests as localized damage or irregularities on the surface of the base metal or nearby areas where the electric arc inadvertently strikes.
Determining Arc Strike Weld Defect:
- Visual Inspection: Arc strikes can often be visually identified by examining the surface of the base metal or nearby areas. Irregularities, such as cracks, pits, or surface discoloration, may indicate the presence of an arc strike.
- Surface Profiling: Surface profiling techniques, such as magnetic particle inspection (MPI) or liquid penetrant testing (PT), can be employed to detect surface irregularities or indications of arc strikes.
Radiographic Process:
In some cases, radiographic testing (RT) may not be suitable for detecting arc strikes directly, as they primarily affect the surface of the base metal. However, if the arc strike leads to subsurface damage, such as cracking or internal defects, radiographic testing can be used to identify these issues.
Prevention Strategies:
- Electrode Manipulation: Proper electrode manipulation and control of the welding arc are essential to prevent arc strikes. Welders should maintain a consistent arc length and angle to minimize the risk of the arc inadvertently striking the base metal or nearby areas.
- Workpiece Preparation: Ensure proper workpiece preparation, including cleaning and grinding, to remove any surface contaminants, oxides, or coatings that may contribute to arc strikes.
- Fixture and Shielding: Use appropriate fixtures, clamps, or shields to protect adjacent areas of the workpiece from accidental arc strikes. Shielding techniques, such as the use of backing bars or sacrificial materials, can help prevent arc strikes on critical surfaces.
Impact on Weld Quality:
Surface Integrity:
Arc strikes can compromise the surface integrity of the base metal, leading to localized damage, surface irregularities, or contamination, which may affect the aesthetics and corrosion resistance of the welded component.
Repair and Rework:
Depending on the severity of the arc strike, repair or rework may be necessary to restore the surface integrity of the affected area. This can result in additional costs and delays in the welding process.
Conclusion:
Arc strikes are weld defects that require careful attention to welding procedures, electrode manipulation, and workpiece preparation to prevent. Through thorough inspection and testing, including visual examination and surface profiling techniques, welders and inspectors can ensure the reliability, safety, and quality of welded components, such as pressure vessels, and mitigate the risk of these defects.
