MIL-HDBK-1003/8A
Table 9
Reasonable Velocities for Flow of Steam in Pipes
CONDITION
PRESSURE
SERVICE
REASONABLE
OF STEAM
(psig)
VELOCITY [1]
(fpm)
Saturated
Vacuum
Turbine exhaust
Up to 18,000
0 to 25
4,000 to 6,000
25 and up
Steam distribution
6,000 to 10,000
125 and up
Underground steam
distribution
Up to 20,000
Superheated
200 and up
Boiler and turbine
leads
7,000 to 20,000
[1] Velocities should be below those which would produce excessive noise
or erosion.
d) Steam Distribution Pressures. Steam pressure is governed by
the highest pressure needed by the equipment served at the most remote
location as well as by an economic analysis of the feasible systems, including
pressure considerations. The advantages of a low-pressure system (under 15
psig) (103.4 kPa) are low distribution loss, lower losses and less trouble
from leakage, traps, and venting, simplified pressure reduction at buildings,
standard steel fittings, and low maintenance. The advantages of high-pressure
distribution, over 50 psig (344.5 kPa), are smaller pipe sizes, availability
of steam for purposes other than for heating, and more flexibility in
velocities and pressure drops.
e) Selection of Valve Types. Install double-ported, pilot-
operated valves for large capacities, especially for inlet pressures above 125
psig (861.3 kPa). Double-ported valves will not shut off completely on no-
load demand; therefore, single-seated valves must be used for such services.
Do not install reducing valves on the basis of pipe sizes, because oversized
valves do not give satisfactory service. Select valves to operate generally
fully open, with ratings and reduction ratios as recommended by the
manufacturer. Install a strainer and condensate drain ahead of the pressure-
reducing valve. Because the volume of steam increases rapidly as the pressure
is reduced, a reducing valve with increased outlet or expanding nozzle is
required when the reduction ratio is more than 15 to 1. Provide cutout valves
to isolate the pressure reducing valve to permit maintenance. Where the
resulting superheated steam temperature is objectionable to the process on the
low pressure side or the temperature-use limit of the equipment has been
exceeded, a desuperheater must be used to lower the steam temperature to that
for saturation. Provide a manual bypass for emergency operation when the
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