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Steam Pipes - Online Pressure drop Calculator

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The pressure drop in a saturated steam distribution pipe line can be calculated in metric units as

dp = 0.6753 106 q2 l (1 + 91.4/d) / ρ d5                                           (1)


dp = pressure drop (Pa)

q = steam flow rate (kg/h)

l = length of pipe (m)

d = pipe inside diameter (mm)

ρ = steam density (kg/m3)

The Unwin formula can also be expressed in imperial units as

dp = 0.0001306 q2 l (1 + 3.6/d) / (3600 ρ d5)                                                  (2)


dp = pressure drop (psi)

q = steam flow rate (lb/hr)

l = length of pipe (ft)

d = pipe inside diameter (inches)

ρ = steam density (lb/ft3)

Use values for the specific volume corresponding to the average pressure if the pressure drop exceeds 10 - 15 % of the initial absolute pressure.

Note that for elevated velocities the Unwin's formula is known to give pressure drops higher than the actual.

Example - Pressure Drop in a Steam Pipe

A steam flow 4000 kg/h with pressure 10 bar (1000 kPa) and density 5.15 kg/m3 flows through a schedule 40 ND 100 steel pipe with inside diameter 102 mm and length 100 m. The pressure drop can be calculated as

dp = 0.6753 106  (4000 kg/h)2  (100 m) (1 + 91.4/(102 mm)) / ((5.15 kg/m3)  (102 mm)5 )

    = 36030 Pa

    = 36 kPa


Steam Pressure Drop Calculator - Metric Units

Steam Pressure Drop Calculator - Imperial Units


Pressure Drop Diagrams - metric units

The diagrams below can be used to indicate pressure drop in steam pipes at different pressures. The calculations are made for schedule 40 pipe.

  • 1 bar = 100 kPa = 10,197 kp/m2 = 10.20 m H2O = 0.9869 atm = 14.50 psi (lbf/in2)
  • 1 kg/h = 2.778x10-4 kg/s = 3.67x10-2 lb/min

Steam - pressure 1 bar gauge

Steam - pressure 3 bar gauge


Steam - pressure 7 bar gauge

Steam - pressure 10 bar gauge

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