According to CSA W59, surfaces and edges that are to be welded must be free of slag, rust, paint and so forth within how many millimeters of the weld to prevent contamination?

• A. 25 mm
• B. 50 mm
• C. 75 mm
• D. 100 mm

Answer: (B)

Keeping the weld area free of slag, rust, paint, oil, and other contaminants within 50 mm of the weld is required. This 50 mm buffer helps prevent any surface contaminants from entering the molten weld pool or becoming trapped in the solidifying weld metal, which can cause porosity, inclusions, poor fusion, or hydrogen-related cracking. By cleaning the joint surfaces thoroughly in that zone, you promote better weld quality and consistent penetration. Practically, you’d remove coatings and contaminants from the joint region about 50 mm on either side of the weld seam. A smaller distance could let contaminants affect the weld, while a larger distance isn’t necessary to meet the standard and would be more restrictive without added benefit.