Travel speed and heat input calculator

Insert the time taken to complete the weld and the weld length into section 1. Enter your recorded welding amps and volts into section 2, and select the process. The calculator returns travel speed, arc energy and heat input as three separate figures, because arc energy and heat input are not the same number and quoting the wrong one against a procedure limit is how a compliant weld fails an audit.

Nothing you type leaves your browser. This runs in the page, in JavaScript. Your recorded welding parameters are not transmitted, stored or logged. Why that matters.

The calculator

The two sections are chained: section 1 produces the travel speed that section 2 uses. If you already know the travel speed, enter a weld length and the time that produces it, for example 300 mm and 120 seconds for 150 mm/min.

1. Travel speed

Input the time taken and the length of weld.

Weld time, seconds

Weld length, mm

2. Arc energy and heat input

Input the recorded amps and volts.

Welding current, amps

Arc voltage, volts

Welding process
Sets the thermal efficiency factor k

Result

Updates as you type

Calculated travel speed: –mm/min
Arc energy: –kJ/mm
Heat input, k = 0.8: –kJ/mm
Arc energy is what the arc delivered. Heat input is what went into the joint, arc energy multiplied by the process thermal efficiency k. They are two different quantities, so check which one your welding procedure or the applicable standard is limiting before you write a number on a record.

Formula and assumptions

Travel speed

Travel speed = weld length (mm) / weld time (s) x 60 [mm/min]
Arc on time for the run, not the shift. Time spent changing electrodes, chipping slag or repositioning does not belong in this figure.

Arc energy and heat input

Arc energy = (amps x volts x 60) / (travel speed (mm/min) x 1000) [kJ/mm]
Heat input = k x arc energy [kJ/mm]
The 60 converts minutes to seconds, the 1000 converts joules to kilojoules. Equivalently, arc energy in kJ/mm is amps x volts divided by travel speed in mm/s divided by 1000.

Arc energy is not heat input

This is the distinction the previous version of this calculator did not make, and it matters.

Arc energy is the electrical energy the arc delivered per unit length of weld. It is a measured quantity: amps, volts and travel speed, nothing else.
Heat input is the energy actually transferred into the workpiece. It is arc energy multiplied by a thermal efficiency factor k, which accounts for the energy lost to radiation, convection and spatter rather than entering the joint.

The practical consequence: for MMAW at k = 0.8, heat input is 20 per cent lower than arc energy. If a welding procedure limits heat input to 2.0 kJ/mm and you record an arc energy of 2.2 kJ/mm as though it were heat input, you have written yourself a non-conformance on a weld that actually complied. Run the same mistake the other way, against a procedure that limits arc energy, and you have recorded 1.76 where the limit was 2.0 and hidden a genuine excursion. Either way, an auditor who asks which quantity your record holds and gets a shrug will keep pulling on the thread.

Thermal efficiency factors

The values used here follow the conventional process factors in ISO/TR 18491 and the treatment in AS/NZS 1554.1. The default is MMAW, so it is never ambiguous which factor is in play when the page loads.

Thermal efficiency factor k by process
Process	k
Submerged arc welding, SAW	1.0
Manual metal arc, MMAW or SMAW	0.8
MIG and MAG, GMAW	0.8
Flux cored, gas shielded, FCAW	0.8
Flux cored, self shielded, FCAW	0.8
TIG, GTAW	0.6

Assumptions

Steady state, single run. One run, one set of parameters, constant travel speed. A weave and a stringer at the same amps and volts do not produce the same heat input, because the travel speed differs, so measure the run you are actually reporting.
Recorded, not set, values. Use the amps and volts read at the arc during welding. Machine dial settings and open circuit voltage are not the same thing.
Waveform controlled processes need a meter that can follow them. For pulsed GMAW and other waveform controlled processes, an averaged reading from an ordinary meter can be well out. Instantaneous power measurement is the correct method where the procedure limit is tight.
Arc on time only. Weld time is arc on time for the length entered.
A zero or blank time gives a dash, not infinity. All four inputs have to be present and greater than zero before a figure appears.

Worked example

A 300 mm run completed in 120 seconds, recorded at 180 amps and 24 volts, MMAW, k = 0.8.

travel speed = 300 / 120 x 60 = 150.0 mm/min
arc energy = (180 x 24 x 60) / (150 x 1000)
= 259200 / 150000 = 1.728 kJ/mm
heat input = 0.8 x 1.728 = 1.382 kJ/mm

The old calculator returned 1.728 and labelled it heat input. It was reporting arc energy. Both numbers are on this page, each with its own label, so a record made from it says what it means.

Where this sits against the standards

Structural steelwork. AS/NZS 1554.1 controls heat input where the steel type and the required mechanical properties make it an issue, and it interacts with preheat and with interpass temperature rather than standing on its own.
Procedure qualification. Heat input is an essential variable under ISO 15614. A qualified range is a range, and running outside it means requalification, not an explanation.
Pressure equipment. AS 1210 and AS 4041 pick up heat input through the procedure and through impact test requirements where they apply.
Recording it. AS/NZS ISO 3834 requires the welding parameters to be specified, controlled and recorded. That is where the arc energy against heat input distinction stops being academic: the record has to state which quantity it holds.

Carbon equivalent, preheat and heat input are all part of the same decision. The carbon equivalent calculator covers the composition side of it.

Disclaimer

AWI provides this calculator as a free resource to the welding industry. Validate the accuracy of any result before relying on it. AWI accepts no responsibility for consequent losses from the use of these resources.