Welding slag is a vitreous material produced as a byproduct of some arc welding processes, such as shielded metal arc welding (SMAW), submerged arc welding, and flux-cored arc welding. It is formed when flux, the solid shielding material used in the welding process, melts in or on top of the weld zone.
The dangers of welding slag
Welding slag can pose several dangers to both the welder and the welded material. Some of the risks associated with welding slag include:
- Slag inclusions: These do not contribute to the strength or protection of metals after being welded and are considered waste inside the weld metal. They can inhibit the inspection of the weld area, have a negative visual appearance, and weaken the next weld layer that is applied.
- Effect surface treatment processes: If slag is not adequately removed, it can lead to premature coating/plating failure. This can occur due to corrosion formed around the poorly coated/plated areas or by the spatter being knocked off.
- Eye and face hazards: Welding slag can cause impact trauma and lacerations to the eyes and face from flying particles and burns from hot slag or particles.
- Welding defects: Slag can contribute to the formation of welding defects, such as incomplete fusion, which can be catastrophic and lead to leaks or collapses.
To avoid welding slag, you can follow these best practices:
- Choose the right welding process: Some welding processes produce more slag than others. For example, shielded metal arc welding (SMAW), submerged arc welding, and flux-cored arc welding are more likely to produce slag than other processes. If possible, consider using a welding process that produces less slag.
- Use proper welding techniques: Ensure that you are using the correct welding technique and parameters for the specific welding process you are using. This can help minimize the amount of slag produced.
- Use self-peeling slag filler materials: Some filler materials are designed to include self-peeling slag that releases itself from the weld. This can help reduce the amount of slag that needs to be removed after welding.
- Remove slag during multi-pass welds: When performing multi-pass welds, always fully remove the slag after each pass to prevent it from being trapped inside the weld during subsequent passes.
- Use proper welding consumables: Choose high-quality welding consumables that are designed for the specific welding process you are using. This can help minimize the amount of slag produced and improve the overall quality of the weld.
Removal of slag is usually done using manual or power tools. Manual tools include welding or chipping hammers and wire brushes, while power tools include angle grinders with grinder disks or wire brush wheels.
Welding slag can be harmful to both metals and welders. Therefore, it’s crucial to monitor for slag during/after the welding process to ensure a smooth, slag-free surface.
