0.5 percent sulfur, a casing type enclosure is
suitable.
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Boiler walls shall be [steel-encased wall construction with fabrication
details as recommended by the boiler manufacturer. Boiler wall and boiler
roof lining shall consist of a continuous screen of closely spaced finned,
tangent, or intermittent watertubes. Steel-encased walls shall have casing
constructed of not thinner than 3.416 mm 10 gauge black steel sheets,
either bolted or welded. Casing shall be gas-tight and shall be reinforced
with structural steel to provide rigidity and prevent buckling. Provision
shall be made for expansion and contraction. [Refractory behind the
waterwall tubes shall be high-duty refractory, not less than 63.5 mm 2-1/2
inches thick.] High temperature block and mineral wool blanket insulation
shall be provided between the refractory backup and steel casing, or
between an inner and outer casing, and shall be of sufficient thickness to
limit the maximum casing temperature in the furnace area to [54] [_____]
degrees C [130] [_____] degrees F with a surface air velocity of 508.0
mm/second 100 fpm and an ambient air temperature of 27 degrees C 80 degrees
F when operating at full capacity. When boilers are provided with double
casings, the inner casing shall be constructed of not thinner than 1.897 mm
14 gauge steel sheets. Alloy steel conforming to ASTM A 568/A 568M shall
be used where temperatures over 370 degrees C 700 degrees F occur.] [of
welded wall construction. The width of the fins shall be limited to 20 mm
3/4 inch to prevent overheating of the fins under all operating conditions.
Designs exceeding 20 mm 3/4 inch may only be used when provided with
supporting calculations and subject to the approval of the Contracting
Officer. Tubes shall be seamless type. The fin-to-tube weld shall be
continuous and on both the front (fireside) and back side of the fin. The
fin shall not be less than 6.4 mm 1/4 inch thick. The construction shall
form a pressure-tight structure capable of transferring a maximum amount of
heat to the tube. All welded joints and openings shall be checked by a
pressure test. Any casing leakage shall be repaired and made
pressure-tight. The maximum deflection of the reinforced panels shall not
exceed 1/360 of the length of the maximum span. The structure tested shall
be capable of holding a pressure of 1-1/2 times the predicted maximum
furnace operating pressure.]
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NOTE: For personnel safety, the design temperature
of the casing surface should not exceed 66 degrees C
(150 degrees F). Should the designer wish to use a
design surface temperature between 54 and 66 degrees
C (130 and 150 degrees F), an economic evaluation
must be performed. The evaluation must determine if
the additional capital costs for insulation outweigh
the cost savings due to reduced boiler radiation
losses.
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a.
Boiler roof shall have a casing constructed of not thinner than
3.416 mm 10 gauge black steel sheet. Refractory lining shall
consist of 63.5 mm 2-1/2 inches, minimum, of high-duty refractory
backup behind the roof tubes and sufficient thickness of high
temperature block insulation or mineral wool blanket to limit the
maximum casing temperature in the furnace area to [54] [_____]
degrees C [130] [_____] degrees F with a surface air velocity of
508.0 mm/second 100 fpm and an ambient air-temperature of 27
degrees C 80 degrees F when operating at full capacity. Exposed
SECTION 15559A
Page 24
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