Arc strike, also called arc burn, is a welding defect that occurs during the welding process when an electric arc unintentionally contacts the base metal or a previously deposited weld bead in an area where it is not intended to be applied. This can happen when a welder initiates the welding arc at the wrong location or accidentally touches the electrode or filler material to the wrong area before the proper welding position is established.
Arc strike is an arc initiated (accidental or intentional) on the base metal surface away from the weld zone. The arc strike is a critical discontinuity because there is a localized area where the base metal has been melted and then rapidly cooled due to the massive heat sink created by the surrounding base metal. This changes the structure of the base metal and causes it to become hard and brittle. This can lead to cracking which could lead to failure of the weldment.
Arc strikes can lead to various issues and concerns
- Contamination - The arc can melt and fuse the base metal or the previous weld, causing contamination. This can negatively affect the mechanical properties and integrity of the welded joint.
- Cracking - The rapid heating and cooling caused by an arc strike can result in localized thermal stress, potentially leading to cracks in the welded area.
- Weakened Weld - The presence of an arc strike can weaken the weld by introducing defects and irregularities in the weld bead.
- Inconsistent Weld Appearance - Arc strikes can create irregularities in the weld's appearance, making it look uneven and unsightly.
- Reduced Weld Quality - Depending on the severity of the arc strike and the welding application, the overall weld quality and performance can be compromised.
All arc strikes should be removed by grinding. Grinding to a depth of 1/8 inch below the original surface should remove all traces of arc strikes and their hardened heat-affected zones. In locations where the arc strikes have been removed should have magnetic-particle inspection and hardness testing performed.
To prevent arc strikes, welders use proper techniques and positioning when initiating and maintaining the welding arc. This includes ensuring that the arc is started in the intended location and that the electrode or filler material doesn't accidentally touch the base metal outside the desired weld zone. Welders also wear protective gear, such as gloves and helmets, to prevent accidental contact between the electrode and their skin. In industries where weld quality and integrity are crucial, proper training, adherence to safety protocols, and attention to detail are essential to minimize the occurrence of arc strikes and other welding defects.