In the heat input calculation, travel speed is measured in which units?

• A. Feet per minute
• B. Inches per minute
• C. Centimeters per minute
• D. Meters per minute

Answer: (B)

When you’re calculating heat input, you’re linking the electrical power delivered to the weld (voltage times current) with how long that heat is applied per unit length of weld. Power is in watts (joules per second), so to get energy per inch you multiply by the time the arc spends on each inch of weld. The time per inch is the inverse of travel speed, and since the common formula uses the 60-second minute factor, the travel speed must be in inches per minute to keep the units consistent. Using inches per minute makes the constants in the formula straightforward (energy per inch comes from watts times seconds per inch). If you used a different length unit, you’d have to adjust the constants accordingly. So travel speed is measured in inches per minute.