HLY-OP-03: 4-Stage Steam Curing Thermal Valve Control & Recording SOP

1. Pit Enclosure & Pre-Steaming Delay

Place green pipes into pit; lower insulated covers; verify water-trough perimeter seals are flooded to prevent steam escapes.

Mandatory Delay: Dwell for 2.0 hours without steam injection. Record time and ambient temperature on curing log.

Step-open main steam valve incrementally every 30 minutes.

Strictly regulate temperature ramp rate to $\le$ 15°C–20°C / hour. Heating from 20°C to 70°C must take $\ge$ 2.5 hours.

Regulate temperature at 68°C–72°C (never allow temperatures to exceed 78°C!).

Maintain relative humidity $\ge$ 95%; soak for 3.5 to 4.0 hours.

Log temperature sensors across all 4 quadrants every 45 min; balance manifold branch valves if differential exceeds 5°C.

Close steam valve; throttle vent dampers to cool at $\le$ 15°C / hour.

Do not lift pit covers until internal pit temperature is within 20°C of factory ambient air.