Insulation Thickness Calculator

Units

Inputs

NPS (pipe size)

OD will show below.

Process temperature (T_process)

Use a negative value for cold / cryogenic service.

Ambient temperature (T_amb)

Target surface temperature (T_surf)

Personnel protection: 60°C. Cold service (anti-condensation): > ambient dew point.

Insulation material (k)

Outer surface heat transfer coefficient (h_o)

h_o combines convection + radiation. Use 8–10 for typical indoor / sheltered outdoor service.

Result

Required insulation thickness

—mm

Resulting outer dimensions

—

Heat loss / gain at this thickness

—W/m

Verification — surface temp at this thickness

—

Formula & Method

Steady-state heat balance: q⁄L = 2πk(T_p − T_s) / ln(r_o/r_i) = h_o · 2πr_o · (T_s − T_amb) Solve iteratively for r_o; insulation thickness = r_o − r_i.

Method: conduction through cylindrical insulation balanced against combined convection + radiation at the outer surface. Steel pipe wall resistance is negligible compared to insulation and is neglected, consistent with ASTM C680 Annex A.

Variables:

k = insulation thermal conductivity (W/m·K)
r_i = pipe outer radius = OD/2 (insulation inner radius)
r_o = insulation outer radius (what we solve for)
h_o = outer surface heat transfer coefficient (convection + radiation lumped)
T_p, T_amb, T_s = process / ambient / target surface temperatures

Common targets:

Personnel protection (hot service): T_surf ≤ 60°C (ASTM C1055)
Anti-condensation (cold service): T_surf ≥ ambient dew point (typ. +5°C margin)
Energy / heat-loss: economic thickness from ASTM C680 / ISO 12241
Process control: keep fluid above pour point or below decomposition temperature

Conservatism: result is for bare straight pipe. Add 10–15 mm for fittings, valves and supports where heat-loss is concentrated. Field thickness is also stepped to standard insulation pre-formed sizes (25, 38, 50, 63, 75, 100, 125… mm).

Brownfield tip: retrofit insulation almost always finds CUI (Corrosion Under Insulation) underneath. Budget for surface prep, primer and sometimes new pipe before quoting just the insulation. Carbon steel between 60°C and 175°C is the worst CUI risk window — specify CUI-grade vapor stops at every penetration.