In welding pipeline under pressure, based on API 1104, the WPQR calculates the heat input produced for the test specimens welded. But HI is not considered an essential variable in the API 1104, whereas I, V and welding speed are. So how to set a limit for HI when welding in service based on the WPQR?

The short answer is tha the codes list the minimum requirements. It is up to the user to be intelligent enough to know what additional information is necessary to produce satifactory welds.

Al