-––
[
OPERATIONAL & DESIGN
CONSIDERATIONS]
–-–
The following background information on the plant and detrimental to the design of the flexible element and
application can have significant influence to the design should be avoided.
life of the expansion joint.
PRESSURE & EXPANSION ■
Plant type
JOINT LEAKAGE
■
Location of expansion
Fabric expansion joints are typically designed for low
■
Environmental conditions
pressure duct systems with maximum rating at +5 psig
■
Base or peak load plant
for elastomeric and +3 psig for fluoroplastic and
■
Relevant history of existing and adjacent equipment
fluoroelastoplastic belts.
FLOW MEDIA
Fabric expansion joints are designed to be as leak tight
In defining system media, the designer should specify
as practical. When an unusual amount of liquid is
the type of fuel, sulfur content, and any additives,
present within the ducting, or leakage requirements are
cleaning agents or catalysts, which may be used in the
specified, special caulking or gasket materials can
system. Ph in the vicinity of the expansion joint should
be used when attaching the fabric element to attain the
be specified, if known, especially if the media is
desired results. In industrial applications, minor leakage,
extremely acidic or caustic.
detectable by soap bubble solution, is considered
acceptable.
The probability of condensation should be determined
by comparing dew point and normal operating
When replacing a fabric element, leakage through bolt
temperatures. Even in systems which normally operate
holes is minimized if holes are aligned and punched
quite hot, shutdowns and startups may produce
in the field as opposed to prepunching the holes at
condensation resulting in excessive corrosion. This
the factory. Backup bar bolts should be tightened to
condition can also occur on the outside of the steelwork
35 to 45 ft. lbs. (45-61 Nm) to ensure optimum
and should be considered.
clamping pressure.
Abrasive components of the media such as flyash should
MOVEMENTS
be identified. Flyash buildup within a flue gas duct
Various movements resulting from thermal expansion
should be estimated, and the dead weight calculated to
of the breeching, both Maximum Continuous System
determine the maximum load on an expansion joint
Operating Temperature (MCSOT) and excursion
element. Plant operating procedures such as duct
temperatures should be specified. Contractions of the
cleaning (wash-down or vacuuming) are also considered
breeching due to cold winter shutdowns, mechanically
in the design.
induced movements such as fan and equipment
vibrations, and structural deflections due to wind loads
TEMPERATURE
and seismic events must also be specified.
Temperatures affect the selection of fabric expansion
joint materials. The following temperatures for the
Movements in various directions should be analyzed to
system should be provided to the engineer.
determine if they occur simultaneously or if they can
■
Normal operating temperature
occur individually without a corresponding deflection in
another direction. The designer to make certain that the
■
Maximum continuous operating temperature
expansion joint design is capable of absorbing a
■
Design temperature
combination of the total maximum movements should
■
Excursion temperatures and duration
specify maximum installation misalignment.
■
Ambient temperatures (the lowest, highest
and average)
SYSTEM GEOMETRY/INSTALLATION
■
Dew point temperatures
The geometry of the expansion joint system, including
Caution: Specifying a “design temperature” which duct size, orientation, material and attachments all have
includes excessive safety factors may actually be an effect on the selection of expansion joint frame
9
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