PRIME MOVERS AND, POWER PLANT MACHINERY.
Under normal conditions steam piping should be of such size that
the maximum velocity of the steam passing through is about 6,000
feet a minute. However, at some installations using superheated
steam the pipe velocities approach 10,000 feet a minute. To use
steam velocity alone in determining the diameters of steam lines
is not always satisfactory, as the length of pipe and the loss of pres-
sure through friction should be taken into. consideration. Too large
a pipe increases the initial cost and the heat losses; too small a pipe
increases the pressure drop due to friction. Steam lines should be
so installed as to avoid excessive strains from expansion and con-
traction, for these cause leaks at the couplings. Usually certain
parts of the line are firmly anchored, and the expansion is taken
care of at other points by floor stands or wall brackets along which
the pipe can slide, or by flexible hangers, or by long radius bends in
the pipe itself.
Sleeve expansion-joints may be used for large pipes where lack
of space prevents long bends. Valves in steam lines over 6 or 8
inches in diameter should have a small by-pass around them to per-
mit the line to be warmed gradually. Large valves are often hard
to open unless the pressure on both sides is equal. Many large valves
include a by-pass.
To provide for the expansion and contraction of a line delivering
steam from a nest of boilers, each boiler should have a swing-arm
MOISTURE IN STEAM.
Moisture at the end of a long steam line is often attributed to the
priming of the boiler, when it is really the direct result of conden-
sation. The condensed steam gradually collects in low points of
the steam line and is carried along at intervals, acting like entrained
water. In the older oil fields in the hilly regions of Pennsylvania
and West Virginia, where because of the topography the boiler is
often at a distance from the engine, this condition is worst during
winter. At such plants the amount of condensation in winter often
amounts to 10 or 15 per cent of the steam passing through the pipe,
as boiler tests made by oil companies have shown.
Figure 1 is a heat-loss chart for bare steam pipes.
INSULATION OF STEAM PIPES.
Various makeshift devices have been used in the oil fields to
decrease condensation losses in steam lines. Many steam lines are
inclosed in old steel casing, or board or plank boxes. Frequently
these devices are not only worthless but increase heat losses, for if
George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed August 28, 2014.