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Downstream Pipe Recommendations
Downstream considerations are more complex due to
a larger number of variables that are introduced in the
outlet of the SteamForm. The most significant of these
variables includes the addition of spray water into the
steam flow and the expansion of steam as the pressure is
reduced. The following sections describe the necessary
features for properly designing the downstream piping
layout.
Straight Pipe Length
To avoid phase separation and downstream problems,
such as erosion or poor process control, it is necessary
to extend the straight pipe length exiting the SteamForm
to allow for water vaporization prior to the installation of a
pipe elbow. This distance ensures that a sufficient mass
of the water droplets is vaporized in order to prevent
water fallout and insufficient mixing. While this length
varies with each set of design conditions, a conservative
design downstream of the valve prior to installation of the
first pipe elbow is L2, as per the equation below:
Minimum downstream straight pipe length:
L2 = Greater of 10 ft (3m) OR 7 x Nominal Pipe
Diameter
Once a minimum straight distance is obtained, Baker
Hughes recommends installing downstream elbows to
enhance flow turbulence. The downstream elbows assist
in the mixing of spray water within the steam flow and
help achieve an evenly distributed temperature profile. It
is suggested to design the first pipe bend using a long-
radius, chrome-moly elbow to protect against wear and
erosion. An example installation is shown in Figure 2.
Figure 1: Recommended upstream straight pipe length
