Gas preflow and postflow depend on which factor?

• A. Nozzle size
• B. Wind speed
• C. Tungsten size
• D. Amperage

Answer: (B)

Gas shielding effectiveness hinges on environmental air movement. Preflow and postflow are timed to ensure the joint is purged of air before starting the arc and remains protected after finishing until the weld and surrounding metal have cooled enough to resist contamination. When there’s wind or a strong draft, shielding gas can be blown away, so you need longer preflow to purge the area and longer postflow to maintain shielding until solidification, preventing porosity or oxidation. In still air, shorter preflow and postflow work fine because the gas stays in place more easily. While nozzle size, tungsten size, and amperage affect arc stability and heat input, they don’t determine how long you need to flow shielding gas—that depends on the level of ambient air movement.