Steam Pipes  Sizing
Sizing of steam pipe lines  major and minor loss in steam distribution systems.
The pressure available for distribution of steam is the pressure difference between the initial pressure at the boiler, and the required final pressure at the end of the line  at the steam consumer.
The pressure difference available for the distribution system can be expressed as:
p = p_{j}  p_{k} (1)
where
p = available pressure drop (Pa (N/m^{2}), psi (lb/ft^{2}))
p_{j} = initial or boiler pressure (Pa (N/m^{2}), psi (lb/ft^{2}))
p_{k} = final pressure (Pa (N/m^{2}), psi (lb/ft^{2}))
The total pressure drop in the distribution system is a result of friction (major loss) and pressure loss in fittings (minor loss), and can be expressed as:
p_{t} = p_{major} + p_{minor} (2)
where
p_{t} = total pressure drop in the system (Pa (N/m^{2}), psi (lb/ft^{2}))
p_{major} = pressure loss in pipes due to friction (Pa (N/m^{2}), psi (lb/ft^{2}))
p_{minor} = pressure loss in fittings (Pa (N/m^{2}), psi (lb/ft^{2}))
Friction  Major Loss
Major loss  the pressure loss due to friction in a low pressure steam distribution system can be expressed as:
p_{major} = p_{a} l (3)
where
p_{a} = pipe friction resistance per unit length of pipe (Pa/m (N/m^{2}/m), psi/ft (lb/ft^{2}/ft))
l = length of pipe (ft, m)
The pressure drop in a steam pipe can be expressed as
p_{a100} = 0.01306 q^{2} (1 + 3.6/d_{i}) / (3600ρ d_{i}^{5}) (3b)
where
p_{a100} = pressure drop per 100 ft pipe (psig / 100 ft)
q = steam flow rate (lb/h)
d_{i} = inside diameter of pipe (in)
ρ = density of steam (lb/ft^{3})
Loss due to Fittings  Minor loss
Loss due to fittings  minor loss can be expressed as:
p_{minor} = ξ 1/2ρ v^{2} (4)
where
ξ = minor loss coefficient
p_{minor} = pressure loss (Pa (N/m^{2}), psi (lb/ft^{2}))
ρ = density (kg/m^{3}, slugs/ft^{3})
v = flow velocity (m/s, ft/s)
Equivalent length
Minor loss  loss due to fittings can also be expressed as equivalent length:
p_{minor} = p_{a} l_{e} (5)
or
p_{t} = p_{a}(l + l_{e}) (6)
where
l_{e} = equivalent length of the fittings (ft, m)
As a rule of thumb the total pressure drop is about 5 10% of initial pressure per 100 m pipe.
Typical Steam Velocities
 Exhaust steam  20 to 30 m/s (70  100 ft/s)
 Saturated steam  30 to 40 m/s (100  130 ft/s)
 Superheated steam  40 to 60 m/s (130 200 ft/s)
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