For material up to 100 mm thick, roughness shall not exceed how many micrometers?

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

Answer: (C)

Surface roughness like Ra describes how smooth a base-metal surface is, and it directly affects weld quality. A smoother surface promotes even heat transfer, better fusion at the weld root, and reduces the chance of trapping slag, moisture, or contaminants that can lead to defects. For material up to 100 mm thick, the standard sets a maximum Ra of 25 micrometers, ensuring the surface is sufficiently smooth for reliable welding without requiring excessive finishing. If the surface were rougher than this, the weld could exhibit poor root penetration, slag inclusions, or other defects, especially in thicker sections where heat and flow dynamics are more critical. Therefore, 25 micrometers is the appropriate limit.