Depends on what spec you're following but in general: If you're using a furnace make sure it has been surveyed within the last year and the thermocouples have been calibrated within the last 3 months. Calibrations should be NIST traceable. If you're wrapping the joint make sure your thermocouples are in contact with the part at or near the weld. Time at temperature begins and ends at the desired temperature of record. Temperature of record should not vary more than 25 F. Make sure the furnace atmosphere is below 400 F before putting the product in and is below 400 F before taking it out or unwrapping it. For acceptance criteria take a hardness reading in the weld and in the adjacent heat affected zones (within 1/2" of the weld). If you're worried about cracking or depending on the spec you may also need to conduct pwht volumetric NDE and/or surface NDE and/or visual inspection.