BIZOMAT 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. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Pipe outside diameter
- What it is
- The outside diameter of the bare pipe that the insulation wraps around.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the actual outside diameter, not the nominal pipe size (DN).
What this means: Fluid (pipe) temperature
- What it is
- The temperature of the pipe surface under the insulation, taken as the temperature of the fluid inside it.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °C to 800 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Heat loss rises in proportion to the difference between pipe and ambient temperatures.
- Get it right
- Use the normal running temperature, not a short peak.
What this means: Ambient temperature
- What it is
- The temperature of the surrounding air near the pipe.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °C to 60 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must be below the pipe temperature, or the tool stops.
What this means: Insulation conductivity
- What it is
- The thermal conductivity of the insulation material at its mean working temperature, from the manufacturer’s data sheet.
- Units and format
- Enter a number in W/m·K: W/m·K. The form accepts 0.01 W/m·K to 1 W/m·K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.04 W/m·K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher conductivity needs a thicker layer for the same loss.
- Get it right
- Conductivity rises with temperature; use the value at the mean of pipe and surface temperatures.
What this means: Outside surface coefficient
- What it is
- The combined convection and radiation heat transfer coefficient at the outer surface of the insulation or jacket, from a heat transfer reference or your data for the setting.
- Units and format
- Enter a number in W/m²·K: watts per square metre per kelvin. The form accepts 1 W/m²·K to 100 W/m²·K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 W/m²·K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Wind outdoors and a shiny or dull jacket both change it.
What this means: Pipe length
- What it is
- The length of pipe being insulated. It scales the annual loss, saving and installed cost.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 100000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hours per year
- What it is
- The number of hours per year the pipe carries hot fluid, from operating records or the shift pattern.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 8784 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6000 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Annual cost of loss and saving rise in proportion; payback falls.
What this means: Energy price
- What it is
- The cost of one kilowatt-hour of heat delivered to the pipe, allowing for fuel price and boiler efficiency, from your energy team or bills.
- Units and format
- Enter a number in $/kWh: money per kilowatt-hour. The form accepts $0/kWh to $10/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $0.08/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Savings rise in proportion and payback falls.
- Get it right
- Use the cost of heat, not the electricity tariff, unless the heat is electric.
What this means: Largest surface temperature
- What it is
- The highest outer surface temperature you allow, typically for protection against burns, set by your safety requirements or applicable standard.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °C to 200 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from your work health and safety requirements; the tool does not set one.
What this means: Largest heat loss per metre
- What it is
- The largest heat loss per metre of pipe you accept, from an energy target, process temperature drop limit or specification.
- Units and format
- Enter a number in W/m: W/m. The form accepts 0.1 W/m to 10000 W/m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 W/m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Insulation thickness chosen
- What it is
- The insulation thickness you intend to fit, measured radially from the pipe surface to the outside of the insulation.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Thickness is radial, not the added outside diameter: the outside diameter grows by twice it.
What this means: Installed insulation cost
- What it is
- The installed cost of insulating one metre of pipe, including material, jacketing and labour, from a quotation.
- Units and format
- Enter a number in $/m: money per m. The form accepts $0/m to $10000/m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $30/m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Payback is proportional to installed cost.
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.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Economic insulation thickness
In Heat Transfer by the Numbers
What it covers: Choose how thick to insulate by weighing installed cost against the value of heat saved: annual losses, simple payback, marginal payback, discounted totals and the effect of a higher heat price.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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