KEVOS® MAKEOS · Materials
Pipe Insulation Design (Thickness for Surface Temperature and Loss, Payback)
How thick must the insulation on this hot pipe be to keep the surface safe and the heat loss within target, and how quickly does it pay back?
Design of insulation on a hot pipe: heat loss per metre, surface temperature and annual energy cost for a thickness (as the insulated pipe tool), the least thickness that keeps the surface at or below your touch limit and the least that holds the loss per metre to your target (found by search), the governing thickness, and for the thickness chosen the saving against the bare pipe and the simple payback on the installed cost.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pipe outside diameter | mm | Outside diameter of the pipe. |
| Fluid (pipe) temperature | °C | Temperature of the pipe (taken as the fluid temperature). |
| Ambient temperature | °C | Surrounding air temperature. |
| Insulation conductivity | W/m·K | Thermal conductivity of the insulation at its mean temperature. |
| Outside surface coefficient | W/m²·K | Combined convection and radiation coefficient at the outer surface (about 8–12 still air indoors, more outdoors). |
| Pipe length | m | Length of pipe. |
| Hours per year | h | Hours per year the pipe is hot. |
| Energy price | $/kWh | Price of the heat energy (fuel or steam cost per kWh). |
| Largest surface temperature | °C | Highest surface temperature you allow for personnel protection. |
| Largest heat loss per metre | W/m | Largest heat loss per metre you accept. |
| Insulation thickness chosen | mm | Insulation thickness you intend to fit. |
| Installed insulation cost | $/m | Installed cost of the insulation per metre of pipe. |
Method and formulas
- Resistance per metre R = ln(r₂ ÷ r₁) ÷ (2πk) + 1 ÷ (2π r₂ h); loss q = (T_i − T_a) ÷ R; surface T_s = T_a + q ÷ (2π r₂ h) (as the insulated pipe tool).
- Least thickness for T_s ≤ limit and for q ≤ target found by bisection; the larger governs.
- Saving = (q_bare − q) × L × hours × price; payback = installed cost ÷ saving.
- Example: 50 mm of insulation cuts the loss from 246.27 to 31.794 W/m, keeps the surface at 26.313 °C, and pays back in 0.29141 years.
Limitations
- Steady state with the pipe wall neglected; fittings and valves lose much more per metre.
- For small pipes with poor insulation, check the critical radius (insulation can raise the loss).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose insulation thickness for a steam or hot-oil line
- Make a pipe safe to touch
- Justify insulating bare pipework
Who it is for
- Plant engineers
- Energy managers
- Maintenance engineers
What you get
- Thickness for surface temperature and for heat loss
- Loss, surface temperature and cost at the chosen thickness
- Saving against bare pipe and payback
Interpreting the result
- The first 25 mm saves most of the heat; extra thickness gives diminishing returns.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–378. Topic reference; no source tables or recommended settings are reproduced.
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