Calculators · Performance Toolkit
Tube Metal Temperature
Estimates outer tube wall temperature from process fluid temperature, radiant heat flux, and tube geometry. Compares the result against the Maximum Allowable Metal Temperature (MAMT) for the selected alloy on an API 530 basis.
Inputs
Tube Material
Determines thermal conductivity and MAMT limit.
Process Fluid Type
Sets the inner film coefficient (hi).
Process Fluid Temperature
°C
Bulk fluid temperature at the point of interest (e.g. coil outlet or hot-spot zone).
Enter a value between 50 and 800 °C
Radiant Heat Flux
kW/m²
Outer tube surface flux in the radiant section. Typical range: 25 – 75 kW/m². Use measured or design value.
Enter a value between 5 and 150 kW/m²
Tube OD
mm
Outer diameter. Typical: 60 – 168 mm.
Enter 25 – 400 mm
Wall Thickness
mm
Minimum measured or as-built wall.
Enter 2 – 50 mm
Wall thickness must be less than tube radius (OD/2)
Results
Enter inputs and press
Calculate TMT to see results
Calculate TMT to see results
Calculation method: Uses cylindrical heat conduction and convective film resistance for a tube heated on its outer surface.
Outer surface temperature:
TMT = Tfluid + ΔTfilm + ΔTwall,
where ΔTwall = q · ro · ln(ro/ri) / k
and ΔTfilm = q · ro / (hi · ri).
Material thermal conductivity values used (at mid-service temperature):
CS 42, 1.25Cr 36, 2.25Cr 32, 9Cr 25, SS304 18, SS316 16 W/m·K
Inside film coefficient (hi) by fluid type:
light liquid 1 500, medium petroleum 800, heavy/viscous 350, gas/vapour 200 W/m²·K
MAMT values are on an API 530 reference basis:
CS 450°C, 1.25Cr 540°C, 2.25Cr 580°C, 9Cr 650°C, SS304/316 750°C
⚠ Results are indicative only, based on simplified engineering relationships and assumed material properties. Not suitable for use in engineering design, fitness-for-service assessment, regulatory submissions, or safety-critical decisions. Actual TMT depends on local flame patterns, fouling, flow distribution, and site-specific metallurgy. Verify all outputs with a qualified engineer using the heater data sheet and measured inspection data.
Related Reference Pages