Mill Utilities
A failed trap makes no noise and no alarm. It just passes a tonne of steam a week.
— kg/h
Napier choked flow through the orifice
The Napier relation assumes choked flow of dry saturated steam through a sharp-edged orifice, and gives an upper bound on the loss: a real trap that has failed partially open, or that cycles, passes less, and a trap passing a mixture of steam and condensate passes less again. Wet steam reduces the mass flow of live steam while raising the total. The orifice diameter should be the trap seat size from the manufacturer data, not the pipe bore. The 750 kWh per tonne is a representative enthalpy above feedwater and varies with pressure and feedwater temperature; for a precise fuel figure use steam tables at the actual conditions. Condensate not returned also carries a water treatment and blowdown cost that is not included here.
Failed Steam Trap Loss, Annual Cost & Survey Payback — free, with the formula and a worked example, at Textile School.