Heat input

[alvaro]

Could someone explain how does heat input affect the mechanical properties of the weldment and how is it measured or calculated?

[Hrushikesh]

Heat input mainly affects the impact properties of the weldment. For any welding there is a specific heat input which gives the higher impact values. Below or above this specific heat input the impact values decrease. Instead the yield and tensile strength of weldment show a monotonic relationship to heat input as they only decrease with increasing heat input.

In addition, higher heat inputs lead to:
1. slow cooling rate,
2. grain coarsening,
3. more melting of filler which can cause to weld metal running ahead of arc leading to lack of fusion problems,
4. overheating of base metal.

The heat input (KJ/mm) is not measured but calculated by (voltage x current x 60) / (1000 x travel speed) where the voltage is measured in "volts", the current in "amps" and the travel speed in "mm/min".

[balamuruganqaqc]

Yes i agree with Mr. Hrushikesh statement but i need to add few points regarding heat input.When any material subjected to impact requirements then the maximum heat input allowed is 25 % above test heat input.
Heat input is mainly influenced by the travel speed, welding position and the welding process.

Cheers,
M. BALAMURUGAN,
ASST. MANAGER (QA/QC),
L&T-MMH CONSTRUCTION,
ODISHA,
PH - +91 8763569606,
Email - balamuruganqaqc@lntecc.com

[Ballbearing]

Mr Balamurugan,
Certain codes allow a percentage increase above the maximum PQR heat input (EN ISO 15614-1).
Certain codes do not allow any increase (ASME IX)
Regards,
BB