Steam Main — Start-up and Running Load

The condensate capacity needed to warm a cold steam main, and the running load once it is up to temperature.

Unit system

Inputs

Nominal pipe sizePipe scheduleLine length

Steam pressure (absolute)

Initial metal temperature

Warm-up time

Warming up slowly both shrinks the trap and reduces thermal shock. 30 minutes is a common target.InsulationInsulation thickness

Ambient temperature

Fittings and supports allowance

Flanges, valves and supports add to the metal mass. Typically 10–30 %.Safety factor

Applied when selecting the trap. A factor of 2 is typical for start-up duty.

Start-up load

163.1kg/h

Running load

10.34kg/h

Trap capacity (with safety factor)	326.3 kg/h
Start-up ÷ running	15.8
Metal mass heated (kg)	1,849
Steam temperature	179.9 °C
Start-up duty	91.28 kW
Heat loss per metre	0.05788 kW
Selection note	The start-up load is many times the running load — sizing the trap on RUNNING duty floods the line and causes water hammer.

A mean specific heat of 490 J/(kg·K) is used for the metal (carbon steel, 20–200 °C).
The running load is for a line fully at steam temperature; during warm-up the loss is smaller.
Condensate is assumed drained evenly along the line. Long mains need drain points every 30–50 m.

A PDF carrying the inputs, results, assumptions and the source. A one-time code is sent to your address.

Results are for engineering pre-assessment and are not a product selection commitment. Final responsibility rests with the user.