Enter the process and ambient temperatures, pipe size, insulation and jacket, then press Calculate. The jacket surface temperature is solved iteratively and checked against the 60 °C touch-safe guideline.
Q/L = 2π·(T1−Ts) / Σ[ln(ro/ri)/ki]
= 2π·r2·[hc(Ts−Ta)+hr(Ts−Tr)] − qsolar
k = k(Tmean) for vendor curves
Engineering tips
- Jacket emissivity: bright aluminium (ε ≈ 0.05) runs hotter but loses less by radiation; painted/ASJ (ε ≈ 0.9) the reverse.
- Touch-safe: personnel protection typically targets a surface ≤ 60 °C — add thickness if the jacket is hotter.
- Cold service: keep the jacket above the ambient dew point and use a continuous vapour barrier to avoid CUI.
Recommended values
- Personnel protection: Keep surface ≤ 60 °C for touchable equipment (≤ 70 °C brief contact).
- CUI zone: Carbon steel −12 to 175 °C is corrosion-under-insulation prone — specify coating and inspection.
- Economic thickness: Increase thickness until marginal energy saving ≈ marginal install cost (payback shown).
- Ambient / wind: Design still-air ≈ 0 m/s indoors; ~5 m/s (≈ 18 km/h) outdoors raises the film coefficient.
Limitations
- 1-D radial: Steady-state single-pipe model — supports, hangers and fittings add bridging beyond the flat allowance.
- Dry system: No wet/damaged insulation, jacket air gaps, or below-dew-point condensation control on the outer skin.
About the standards
- ASTM C680: Standard Practice for Estimate of Heat Gain or Loss.