Min. Qualified Preheat Temperature

Yes. In most processes this is an essential variable and would require anther PQR if you reduce the preheat more than 50Deg C. This is exclusive of any other fabrication/construction code . An examlpe is in B31.1

131.4.2 P-No. 1. 175°F (80°C) for material which
has both a specified maximum carbon content in excess
of 0.30% and a thickness at the joint in excess of 1
in. (25.0 mm). Reheat may be based on the actual
carbon content as determined from a ladle or product
analysis in accordance with the material specification
in lieu of the maximum carbon content specified in
the material specification.

If you are oxyfuel or electrogas welding, this variable can be changed on the WPS without requalification but again, you must follow the requirements of the code of construction.


Gerald Austin
Iuka, Mississippi

Pipewelder1999
Thanks for your reply. But new PQR is necessary for reducing of 50 C from starting preheat temp. in PQR or from Max. temp. during welding in PQR?

If you reduce the minimum temperature more than 50 you need a new PQR.

The "preheat" temp is always a "Minimum temperature before welding"

New PQR is necessary for reducing of 50 C from starting preheat temp. in PQR.

Gerald Austin
Iuka, Mississippi