Failed Steam Trap Loss, Annual Cost & Survey Payback

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 8 inputs are read from the form on every keystroke: Trap Orifice Diameter, Steam Pressure, Traps Failed Open, Operating Hours, Steam Cost, Trap Survey Cost, Boiler Efficiency and Fuel Carbon Intensity.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Steam Lost per Failed Trap together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Survey Payback, Annual Cost of the Failures, Steam Lost, Total Loss Rate, Cost per Failed Trap, Carbon from the Loss, Boiler Fuel Wasted and Orifice Area — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

Twelve traps the size of a pencil lead cost 42,752 a year, and the survey that finds them pays for itself in under a month. The Napier figure checks against the imperial standard: a one-eighth inch orifice at 100 psi is quoted at about 15.5 kg/h in every steam handbook, and this returns 15.9 for the metric equivalent.

How to use it

1. Work through the input groups in order — The Failure and Cost & Carbon. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Steam Lost per Failed Trap in the dark results panel — that is the headline figure, expressed in kg/h.
4. Check the supporting rows underneath (Survey Payback, Annual Cost of the Failures, Steam Lost, Total Loss Rate, Cost per Failed Trap, Carbon from the Loss, Boiler Fuel Wasted and Orifice Area) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Steam Lost per Failed Trap before a trial is booked, so machine time and material in Sustainability, ETP & Utilities are committed against a calculated figure rather than an estimate.
• Costing and quotation — Steam Lost per Failed Trap is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Trap Orifice Diameter) shows how much of the gap in Steam Lost per Failed Trap each variable explains.
• Teaching and study — the accepted ranges bracket normal Sustainability, ETP & Utilities practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• 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.
• Every input is bounded to the range normal practice occupies (Trap Orifice Diameter 0.5 to 20 mm, Steam Pressure 0.2 to 40 bar g and Traps Failed Open 1 to 500, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• ISO 6552 / ISO 6553 - automatic steam traps, definitions and marking.
• BS 845 - methods for assessing thermal performance of boilers, for the fuel-side figures.
• ASME PTC 39 - Steam Traps, performance test code.
• Napier equation for choked steam flow through an orifice, as used in ISO 6552 loss assessment.

Questions people ask