Factors of heat input 1

[weldgal]

In calculating heat input (amps x volts x 60/IPM) on a weld, I'm interested in getting opinions on how much impact preheat and interpass temps have vs. the heat input itself as calculated by the traditional formula shown. None of the technical papers I've found incorporate anything but the four factors in the above formula, so my thought is that while preheat and interpass certainly have a role and cannot be completely discounted, their respective dominance in calculating heat is minimal (i.e., 80% calculated heat input and 20% preheat and IP temps). Any thoughts?

 

[Welder4956]

The V x A x 60 /TS equation is a relative calculation that does not take into account heat transfer efficiency for the welding process or other factors that affect CVN values. It is not intended to be a true measure of total heat input. That would be best obtained using a calorimeter. It is just a means for identifying an obvious change and has been effective for it's purpose. For welding where CVN values are a requirement, increases in interpass temperature are usually an essential variable for welding procedure qualifications and do affect CVN properties.

 

[weldgal]

Thank for responding; so far, we're on the same page. Do you have any reference data that would indicate how big a role preheat and interpass temps have in heat input? While WPSs require preheat mins and interpass maximums, neither preheat nor interpass is a part of the arc energy heat input formula (AxVx60/IPM). Is that because they don't have a very significant effect?

 

[ijzer]

Heat input by welding is calculated as indicated by you. However if you want to use the heat input in calculating the T8/5 time the preheat shall be taken into account , because prehetaing slows down the T8/5.
For reference see the formula's of Rykalin or EN 1011-2 par. D6

 

[metengr]

Go here for T8/5 calcs, and to understand all variables associated with weld cooling rates;

http://homepage3.nifty.com/yurioka/exp.html