If you are talking about Essential Variables for procedure qualification, AWS D1.1-2002 Table 4.5 allows you to have an increase of 10% before requalification. This limit does not apply to GTAW when charpy impact tests are required, in that case no increase is allowed. Most people I believe have always looked at joules/inch as a maximum number.
In ASME Section IX, heat input is viewed as a supplemental essential variable and would only be calculated for those procedures requiring charpy impact tests.

It is mainly an estimate based on the amps, volts and travel speed numbers you plug into the formula. The results depend on whether the amps, volts and travel speed numbers you use are min., max., or average. If you are trying to find a maximum heat input value, use the highest amps and volts, and lowest travel speed recorded. If you are trying to find the minimum heat input, use the lowest amps and volts and highest travel speed recorded.

Marty

Hi Lew

I think that you need to re-phrase the question a little more concisely to get any really good answers. Give us your context and possibly any welding codes involved etc.

Regards
Niekie Jooste
Fabristruct Solutions