Turbines shall also be equipped with a mechanical shaft speed governor and
valve, and independent emergency overspeed governor and trip valve, reed
tachometer, constant pressure type governor, insulation with removable
metal jacket, oil-sight glasses with guards, removable stainless steel
steam strainer [without disconnecting piping], any special wrenches and
tools required for servicing turbine, and a sentinel warning on the exhaust
casings. Turbines shall conform to NEMA SM 23.]
2.11
AIR DUCTS
Air ducts connecting the forced-draft fan units with the plenum chamber
shall chamber shall be designed to convey air with a minimum of pressure
loss due to friction. Ductwork shall be galvanized sheet metal conforming
to ASTM A 653/A 653M. Ducts shall be straight and smooth on the inside
with laps made in direction of air flow. Ducts shall be externally braced
and shall be so installed and anchored as to be free of vibration. Access
and inspection doors shall be provided as indicated and required. Ducts
shall be constructed with long radius elbows having a centerline radius
1-1/2 times the duct width, or where the space does not permit the use of
long radius elbows, short radius or square elbows with factory-fabricated
turning vanes may be used. Duct joints shall be substantially air-tight
and shall have adequate strength for the service, with 38.1 x 38.1 x 3.2 mm
1-1/2 x 1-1/2 x 1/8 inch structural steel angles used where required for
strength or rigidity. Duct walls thickness shall be as follows:
Ducts, Maximum
Steel Sheet,
Dimension
Minimum Thickness
Up thru 1.5 m (60 inches)
1.519 mm (16 gauge)
Up through 60 inches
16 gauge
1.6 m (60 inches) and larger
2.657 mm (12 gauge)
61 inches and larger
12 gauge
2.12
BREECHING
Breeching shall be constructed of not less than 3.416 mm 10 gauge steel
sheets conforming to ASTM A 36/A 36M. Breeching shall be adequately
reinforced and braced with structural steel angles not smaller than 50 x 50
x 6.4 mm 2 x 2 x 1/4 inches, and all joints and seams in the sheets and
angles shall be welded. Expansion joints shall be installed as indicated
and as required to suit the installation and shall be flexible type
requiring no packing. Breeching shall have angle flanges and gaskets for
connection to boilers, fans, equipment, or stacks. Breeching connections
shall be gas-tight and be caulked tight all around and sealed with cement
to form an air-tight joint. Clean-out openings of suitable size and at
approved locations shall be provided for access to all sections of the
breeching and shall have tight-fitting, hinged, cast-iron doors with
cast-iron frames. Plastic materials polyetherimide (PEI) and
polyethersulfone (PES) are forbidden to be used for vent piping for
combustion gases.
2.13
STACKS
Stacks for individual boilers shall be self-supporting double-wall
insulated type. Unless otherwise indicated, each stack shall be complete
with structural steel base, base plates, anchor bolts and nuts, clean-out
door, [induced-draft fan] [boiler] connection and a thermometer well. Stub
stacks for packaged boiler units may be supported directly on the boiler
providing the boiler structure is designed to accommodate such an
SECTION 15559A
Page 59
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