Welding — PWHT cycle
Post-weld heat-treatment T-time profile
ASME VIII UCS-56 / B31.3 §331 PWHT cycle generator. Picks soak T and time per inch of thickness, computes ramp-up + soak + ramp-down + free cool, plots the time-temperature profile.
Inputs
°C
h
ASME UCS-56 typical 1 h/inch · P91 minimum 4 h regardless
°C/h
ASME VIII typical 220 · 200 for P91
°C/h
ASME VIII typical 280 · slower for thick sections
mm
°C
Below this, free-cool to ambient is allowed
P11 piping; 685 °C ± 15
Results
PWHT cycle · soak 685 °C × 1.5 h · ramp 220/280 °C/h
Wall thickness1.50inch
Computed soak time1.50h
Ramp-up duration3.00h
Ramp-down to release0.93h
Total cycle (incl. cool)7.42h
P-Number / clauseP-No 4 Gr 1 (UCS-56-1)
Always document cycle in NDE record (ASME V): heat-up, soak, cool-down rates with thermocouple traces. P91 PWHT "under-cure" is the leading welding-industry failure mode — hold within ±10 °C and 4-h minimum even on thin sections.
Download all inputs + calculations + outputs as a single PDF.