Condensate Load Calculator

• Steam pressure and ambient temperature. The steam pressure sets the saturation temperature T_sat and the latent heat h_fg — the heat released per kilogram of steam condensed (IAPWS-IF97, the international steam-property standard; gauge pressure is converted to absolute by adding 1.013 bar). The ambient / initial temperature is the cold state the metal starts from (Startup) and the air the pipe loses heat to (Running); the temperature rise ΔT = T_sat − T_ambient drives both.
• Startup — equipment mass. Pipe mode takes the wall mass from the schedule database — nominal pipe size (NPS) and schedule fix the outer and inner diameters (OD, ID) per ASME B36.10M — as (π/4)(OD² − ID²) × density × length for the chosen material. Custom mode takes a mass you enter (a vessel, a heat exchanger shell, a manifold with valves). The material sets the specific heat cp: 0.50 kJ/(kg·K) for steel, 0.39 copper, 0.90 aluminium.
• Warm-up time. The warm-up condensate is a fixed quantity — m·cp·ΔT / h_fg kilograms; the time turns it into an average rate. A shorter warm-up means a higher rate the trap must pass, and the rate at the start, when the metal is coldest, is above the average.
• Running — pipe and insulation. Outer diameter, length, insulation material (thermal conductivity k) and thickness. The heat loss is the cylindrical conduction resistance of the insulation, ln(r_outer/r_pipe)/(2πkL), in series with the outer film resistance 1/(h·A) — the surface-to-air convection step; a bare pipe uses the outer coefficient h on the pipe surface directly.
• Wind condition. Sets the outer film coefficient: 10 W/(m²·K) still air, 20 light wind, 40 moderate wind. For an insulated pipe the film is a small share of the total resistance, so wind matters little; for a bare pipe it scales the loss directly.
• Process — heat duty. Either the heat duty directly, or ṁ·cp·(T_out − T_in) of the fluid being heated (water 4.18, light oil 1.9, heavy oil 1.67, 50 % glycol 3.35 kJ/(kg·K), or your own cp). The steam condensed is the duty divided by h_fg.
• Safety factor. A multiplier on the calculated rate for trap selection — 2–3× on startup (air venting, cold-start peaks), 1.5–2× on running (insulation ageing, weather) and 1.5–2× on process (fouling, control swings). It is applied to the rate, not to the physics.
• Outputs. T_sat and h_fg; the mass and cp used; the total warm-up condensate and its average rate; the running heat loss in W and W/m; the process duty; and each rate with and without the safety factor — the with-factor figure is the trap sizing load at the steam pressure.

• Startup counts the pipe wall (or the mass you enter) only — flanges, valves, supports and any liquid contents are extra, and are one reason for the 2–3× factor. cp is constant over the temperature rise.
• Warm-up is treated as adiabatic and linear: no heat loss during warm-up and an even average rate. The real rate is highest at the cold start and falls as the metal warms; a trap must pass the peak, which the factor is meant to cover.
• Running uses a fixed outer film coefficient chosen by wind class (10 / 20 / 40 W/(m²·K)) with the insulation's conductivity constant at its preset value; radiation, the ambient-temperature dependence of natural convection and the temperature dependence of k are not resolved separately.
• The steam-side film, the pipe wall and any cladding are neglected — the insulation and outer film dominate — and the pipe is horizontal in open air: not buried, in a trench, in an enclosed duct or a vertical riser.
• Process condensate is duty ÷ h_fg: the condensate leaves at T_sat with no subcooling credit, and no flash on discharge is subtracted (see the flash-steam calculator for what happens after the trap).
• Steam is dry saturated at the stated pressure; wet or superheated steam changes h_fg slightly. Properties are IAPWS-IF97 up to the critical point.
• This is the load side only. Selecting a trap also needs its rated capacity at the actual differential pressure (inlet minus back pressure) and the trap type for the application; those come from the manufacturer's capacity charts.

The running-loss model is the simplified fixed-h form; for surface temperature, radiation and wind resolved properly use the insulation calculator. The steam properties come from the same IAPWS-IF97 engine as the steam-tables page; the SimuPipe solver's own accuracy is documented on the validation page.

Method and data sources behind this page:

• Spirax Sarco. Steam Engineering Tutorials — Steam Trapping and Air Venting; Condensate Removal. spiraxsarco.com — the startup / running / process condensate-load method and the safety-factor conventions.
• Armstrong International. Steam Conservation Guidelines for Condensate Drainage (Handbook N101) — trap sizing practice and load factors from a trap manufacturer's handbook.
• TLV. Steam Theory — Condensate Recovery and Steam Trap Selection. tlv.com — condensate load estimation and trap selection guidance.
• ASME B36.10M-2018. Welded and Seamless Wrought Steel Pipe — the pipe outside diameters and wall thicknesses the pipe-mass calculation uses.
• IAPWS R7-97(2012). Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam. iapws.org — saturation temperature and latent heat at the steam pressure.
• Incropera, DeWitt, Bergman and Lavine. Fundamentals of Heat and Mass Transfer, Wiley — the cylindrical-wall conduction and film-resistance model for the running loss.