Heat Input on GTAW (duplex)

[drvasquez]

Can the heat input be calculated on GTAW, and if it is what it is the formula? Now do the parts need to be turning to calculate the heat input?

[zapster]

HuH?

...zap!

[Baila La Pinza]

The parts don't have to be turning, you just need to know that the travel speed will stay constant.

Heat input is generally defined by the formula (A x V)/TS
Where A = Current (amps)
V = Voltage (volts)
TS = Travel Speed (mm/s)
The value is normally quoted in kJ/mm.
However, some of the energy generated by the arc fails to reach the weld pool because of radiation losses. To take these losses into account, the heat input formula is multiplied by a thermal efficiency factor related to the type of welding process used.

The thermal efficiency factors are:
Submerged arc: 1.0
MIG, MMA and FCAW: 0.8
TIG and plasma: 0.6 [1]

Also, in case you don't know, with Duplex you need to keep an eye on the interpass temps.

Hope this helps

[Supe]

(Volts x Amps x 60) / (Travel Speed x 1000) will give you KJ/in or KJ/mm. If need be, multiply your final answer by your efficiency factor. Or, for pulsed/waveform controlled power supplies, take your Energy/Bead Length, or (Power (joules per second) x arc time)/Bead Length.

Cooling rates play as big, if not a greater role, than heat input in determining the ferrite/austenite balance in Duplex steels. I have run heat inputs in excess of 100 KJ/in with certain processes without nitrogen mixes, and still retained greater than 35% ferrite.

[anilmele]

Dear Friends
does any one can say heat input of TIG welding or arc welding is more? For keeping a minimum heat input which will be the best option? is there any thump rule for finding heat input of ARC and TIG welding at different current?
Thanks

[Pressure_Welder]

Originally Posted by anilmele

Dear Friends
does any one can say heat input of TIG welding or arc welding is more? For keeping a minimum heat input which will be the best option? is there any thump rule for finding heat input of ARC and TIG welding at different current?
Thanks

Tig does supply a hotter arc, although more concentrated it does put more heat into the base material. For instance on our combustion turbines at our power plant ( huge jet engines) they have inconel liners, when we acquire cracks in them we go into the unit and have to stick weld them with a special alloyed inconel rod.... 1000$ for a 5 pound box! The reason we stick weld it, less heat input and we must closely monitor interpass temps. Tig would be fine on a smaller part as you could preheat / and or have heating blankets on it to maintian welding temp and carry out a post weld heat treatment to stress relieve.