Section I does not have specific limits on heating and cooling rates such as those found in ASME B31.1. Section I paragraph PW-39.3 has the following words:
"The weldment shall be heated slowly to the temperature specified in Table PW-39 and held for the specified time, and shall be allowed to cool slowly in a still atmosphere to a temperature not exceeding 800°F (425°C)."
I would recommend following the B31.1 limits, which is:
"Above 600°F (315°C), the rate of heating and cooling shall not exceed 600°F (335°C) per hr divided by 1/2 the maximum thickness of material in inches at the weld but in no case shall the rate exceed 600°F (335°C) per hr."
B31.1 is acceptable but I find it too conservative for Section I fabrication work. I would follow UCS-56, Section VIII, Div 1 for PWHT heat-up and cool down rates.
