POWER November 2011 - 58

CONDENSER LIFE CYCLE
4. Training time. Staff are trained and qualified
in correct installation methods before starting
a condenser overhaul. Courtesy: RetubeCo
into the tubesheet, and, if required, trimming
and flaring tube ends (Figure 4).
Tube Installation. Scaffolding should be
erected from the tubesheets to extend the full
length of the tubes and to be able to support
several tube boxes. Scaffolding should be independent
at each tubesheet and lowered in 5- or
6-foot increments as tubes are inserted from the
top down. Tube guides are used to guide the
tubes through the support plates. The number
of crews required can vary, depending upon
the number, size, and layout of tubesheets, the
schedule, and available manpower. The crew
size for this evolution is usually about one person
for every 10 to 15 feet of tube length.
Tube Expanding. A tube joint strength test,
serrating of tubesheet holes can be completed
at a high cyclic rate with the right tools and
with little or no schedule impact.
Tube Installation and Expanding
Tube installation and expanding involves
sticking each tube into the condenser, setting
the inlet end of the tube relative to the
tubesheet outer face, expanding the tubes
or pull-out test, is performed to determine the
optimal apparent wall reduction by correlating
tube wall reduction and the torque required to
achieve it with pull-out strength. For the test,
tube specimens from actual tube production lots
are expanded into a mock tubesheet at various
torques. The specimens are then pushed out
with a load cell-equipped hydraulic press, and
the various joint strengths are then calculated
from the apparent tube wall reduction.
The mock-up tubesheet used in the test
can then be used at the site in training and
qualifying personnel to properly expand
tubes using the " known hole method. "
This method utilizes benchmark holes of
the same diameter, simplifying the calculations
required to control the tube-expanding
process. Prior to tube insertion, a
three-ball-type bore gauge is used to locate
and mark 1% of the tubesheet holes with
a common diameter (the " known hole " ).
These holes are marked on the tubesheet
and recorded on a tubesheet map. When
the operator expands a tube in one of these
known holes, the expanded tube ID is measured
and the rolling motor is checked on
a torque analyzer to verify and record that
the proper values are being maintained.
Vibration Mitigation
Finally, it is important that a comprehensive
vibration study be performed when uprating or
changing tube materials in a condenser. Such a
study will determine the need for and the type
of tube staking required. Stakes can be installed
mid-span between support plates in each tube
pitch to effectively shorten the unsupported tube
span and prevent mid-span collision of tubes.
Various stake configurations are available to allow
for a variety of tubesheet patterns. ■
-Ed Overmyer (edo@retubeco.com) is
president of RetubeCo Inc.
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58
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POWER November 2011

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