AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
An inspector is overseeing the fabrication of large pressure vessels using Submerged Arc Welding (SAW). The WPS specifies a wire-flux combination and a travel speed of 20 inches per minute (ipm). If the welding current is 800 amps and the arc voltage is 32 volts, what is the nominal heat input per inch of weld?
- A153.6 kJ/in
- B76.8 kJ/in
- C96.0 kJ/in
- D128.0 kJ/in
Show answer & explanationAnswer & explanation
Correct answer: B. 76.8 kJ/in
Heat input (HI) is calculated as (Voltage × Amperage × 60) / (Travel Speed × 1000) for kJ/in. So, HI = (32V × 800A × 60) / (20 ipm × 1000) = 1536000 / 20000 = 76.8 kJ/in. The factor of 60 converts seconds to minutes, and 1000 converts joules to kilojoules.
Why the other options are wrong
- A. Incorrect calculation, often resulting from misplacing the 60 or 1000 factor.
- C. Incorrect calculation, potentially missing conversion factors or incorrect division.
- D. Incorrect calculation, potentially using an incorrect formula or values.
Heat Input Calculation (kJ/in)
Heat input is a measure of the energy transferred to the workpiece per unit length of weld. It is a critical parameter for controlling microstructure, mechanical properties, and distortion in welding. For arc welding, it's typically calculated using voltage, amperage, and travel speed.
- Formula: HI = (Voltage × Amperage × 60) / (Travel Speed × 1000).
- Units: Volts (V), Amperes (A), Inches per Minute (ipm).
- Resulting unit: Kilojoules per Inch (kJ/in).
- Critical for material properties (e.g., toughness, hardness).
- Conversion factors: 60 (seconds to minutes), 1000 (Joules to Kilojoules).
Memory trick: Volts Amps Time over Speed is your Energy per Length.