Arc energy

Arc energy is the purely electrical half of the heat input calculation: multiply arc voltage by welding current, scale for time and unit length, and divide by travel speed. Nothing about the process itself — how efficiently the arc actually transfers that energy into the joint — enters the number. That is exactly why the term exists separately from heat input, and why treating the two as interchangeable produces disagreements between records that both claim to describe the same weld.

The confusion is a naming split between standard families. ASME and AWS documents compute this unfactored electrical value and call it “heat input” outright. EN and ISO practice reserves “heat input” for arc energy multiplied by a thermal efficiency factor that differs by process — lower for tungsten arc welding, higher for the consumable-electrode gas-shielded processes, higher again for submerged arc — and keeps “arc energy” for the unfactored figure. A production record quoting “heat input” without saying which convention it follows is quoting an ambiguous number, and the gap between the two conventions is widest for the least efficient processes.

Travel speed sits in the denominator, and it is the term most likely to carry error in practice. Voltage and current come off calibrated meters on the power source; travel speed is commonly a nominal program value or a hand estimate, and because arc energy varies inversely with it, an error of a fifth in the speed moves the result further than many qualified bands allow. A wider weave compounds this invisibly: it lowers the true advance rate along the joint without changing what the program or the operator reports as the speed.

Recording arc energy separately from heat input matters most where a qualification record was built under one convention and production monitoring reports under the other. ASME Section IX treats heat input as a controlled variable once impact testing is required, and the value on that qualification record is the unfactored one — a monitoring system reporting an EN-style factored value for the same weld will read lower for reasons that have nothing to do with the weld itself changing. Reading travel speed and heat input alongside arc energy, from measured values rather than from the figures on the WPS cover sheet, is what keeps the comparison honest.