# Importance and Calculation of Heat Input and Arc Energy

##### Importance of heat input: Many reference and construction codes refer for the controlling of heat input during procedure qualifications and further in production also. In general, heat input control is required where impact or corrosion resistance properties are required. ASME section IX also includes heat input in supplementary variables means when the impact testing is required means you have to keep control over parameters related to heat input when impact is specified for the weld.

The important characteristic of heat input is it governs the cooling rate of the welds and therefore effects the microstructure of the weld. It is similar to the preheat, when the heat input is increased the cooling rate of the weld is decreased. Slower cooling rates results in coarser grain size in the weld and HAZ and effects the mechanical properties(specially toughness) of the weld. Coarser grain size of weld and HAZ results in less no. of grain boundaries exhibits less toughness, so it is required to control heat input when toughness properties are to be meet in weld and HAZ.

##### Arc Energy (AE): Arc energy is the energy supplied by the power source to the workpiece i.e.

AE = VI*60/T.S

Where

V is the voltage used, in volts

I is the current used, in amperes

T.S is the travel speed of the welding electrode, in distance per minute (mm/min.)

Units of are Arc Energy is J/mm.

#### Heat Input (H.I) : Heat input is the actual energy reaches to the workpeice it’s calculated by multiplying the thermal efficiency of the process to the arc energy.

Heat Input (H.I.) = ɳ*AE

Where

AE is arc energy in J/mm

ɳ is the thermal efficiency of the process which has no units and is dimensionless.

Thermal efficiency for the different arc welding process are tabulated below

Other methods to calculate heat Input are listed in ASME Section IX are described below

1. Heat Input determined by instantaneous energy/power : Method defined above are useful for DC welding with where welding parameters are not rapidly can be averaged easily but in waveform controlled weld  the heat input cannot be calculated by above mentioned formula due to rapidly-changing outputs, phase shifts, and synergic changes. During waveform controlled welding, current and voltage and values observed on the equipment meters no longer are valid for heat input determination, and must be replaced by instantaneous energy (joules) or power (joules/second or watts) to correctly calculate heat input. For example GMAW-P welding waveform controlled power sources are used. Such welded power source generally shows instantaneous energy or power if not shown by power source external equipment can be used for measuring instantaneous energy or power. Welding power sources or external equipment shows instantaneous energy as a cumulative measure of instantaneous energy ie the sum of instantaneous energy measurements made during a time period such as trigger-on to trigger-off. The units of measurement may be joules (J) or any other equivalent. If machines are not  giving instantaneous energy then below formula against total  power/energy given by welding power source or external equipment can be used

(i) Heat input for instantaneous energy measured in Joules (J)

= Energy (J)/ Weld Bead Length (mm)

(ii) Heat input for instantaneous power measured in Joules (J)

= [Power (J) * Arc Time(S)] / Weld Bead Length (mm)

2. Volume of weld Deposit: As per ASME section IX instead of heat input we can be calculate the volume of weld metal deposited per unit of length of weld for each process. The volume of weld deposited can measured by following methods

(i) By measuring the size of bead i.e. width * Thickness of the weld  bead

(ii) By measuring the length of weld per unit of  electrode

Examples for heat Input calculation:

Example 1: You are using conventional power source welding machine and using GTAW arc welding process. The parameters used for welding showing on machine are current 125A and voltage 13V.  250mm of length is welded in 4 minutes of time. What will be heat input?

First you have calculate travel speed before calculating heat input by applying below mentioned formula

Travel Speed (T.S.) = Length of Weld/ Time Taken to weld = 250mm/4 minutes = 62.5mm/minute

Heat Input (H.I.) = (V*I*60)/T.S. = (13*125*60)/62.5 = 1560J/mm

Example 2: You are using a special waveform on a power source with GTAW process. The reading on the display for energy used for length of 500mm is 560J. What will be heat input?

No need of calculation of travel speed for calculating heat input in this method. We just need to put formula.

Heat Input (H.I.) = Total Energy (KJ)/ Weld Bead length = 560 KJ/ 500mm = 1.12 KJ/mm = 1120KJ/mm.

You can use our heat input calculator for calculating heat input

### 18 thoughts on “Importance and Calculation of Heat Input and Arc Energy”

1. Good nice contribution

2. Very good

3. Anand Sagar Gupta

Simply explained… commendable work…please provide some article on supplementary essential variables from section IX…

4. Knowledgable explanation

5. chirag patel

Easy and clear explanation for heat input calculations.

6. Mohit Aggarwal

Very informative and explained well.

7. Any effect in heat Input in weld if we change the groove detail of weld joint .

1. Heat Input depends upon travel speed, current and voltage. There is no any affect in heat input by changing groove detail and joint design.

8. Highly appreciable

9. Hassen Ahmedniguss

Really excellent explain .
Thanks so much

10. Nicely explained,
Good job Abhishek

1. Pawan sharma oman

11. Good job abhishek and very nice explain. thanks so much .

12. Hii

13. Heat Input, weld energy: well explained. Appriciate your efforts, thanks for sharing the information

14. Ilangkumaran

Great stuff I m sure this will help lot of professionals who do not know how to calculate heat input!