required for proper operation and maintenance. Provide a minimum of one
door above each bus section. The minimum access opening size shall be 460
by 600 mm 18 by 24 inches for rectangular openings and 600 mm 24 inches
diameter for round openings. Provide key interlocks for openings through
which personnel may come in contact with high voltage equipment to prevent
opening before the electrical supply is deenergized. The housing shall be
of all welded construction. Minimize the use of flanged or bolted joints.
Use only where bolted assembly is required for adjustment or removal.
Prevent structural members from acting as radiators, thereby reducing
internal corrosion. The difference between the inside wall temperature at
any point and the inlet gas temperature shall be less than 22 degrees C 40
degrees F.
2.4.1
Penthouse
Provide a penthouse to enclose the high voltage system support insulators.
Enclose the entire top of the housing. Design the penthouse to withstand
the effects of differential thermal expansion between the precipitator
housing and the penthouse. Design the expansion provisions to assure an
airtight penthouse. Weld gas tight. Check for leaks using smoke candles
or other method approved by the Contracting Officer. Repair leaks by
welding or repair of mechanical seals. Do not use caulking. Provide a
minimum of 2 insulated, hinged, quick-opening access doors on the penthouse
roof; one at each end of the roof. Provide penetrations, openings and
hatches in or on the penthouse roof with mechanical seals or weld to
provide a gas tight and watertight seal. Install calcium silicate
insulation conforming to ASTM C 533 over 12 gage steel pines stud welded on
610 mm 2 foot centers on the penthouse roof. Hold in place by 65 mm 2 1/2
inch square speed washers and closely fit around penetrations. Construct
top surface of 6 mm 1/4 inch thick raised pattern plate conforming to ASTM
A 242/A 242M, Type I to form a continuous walking surface. Provide support
to bear not less than 488 kg per square meter 100 pounds per square foot
live load. Provide additional support for equipment placed on the roof.
Seal joints by continuous fillet or complete penetration groove welds as
applicable. Weld appurtenances similarly to the plate. Provide top
penetrations with a 50 mm two inch minimum extension above the plate and
similarly weld to the plate. Slope the top surface to allow water runoff
and to prevent pooling. Extend top surface at least 25 mm one inch beyond
side insulation. Provide a 80 mm 3 inch fascia of 6 mm 1/4 inchsteel
conforming to ASTM A 242/A 242M plate as a rain barrier. Provide a 80 mm 3
inch kickplate of 6 mm 1/4 inch steel conforming to ASTM A 242/A 242M plate
around the perimeter of the top surface and provide adequate drain holes to
permit water runoff. Provide a safety rail on the top perimeter.
Manufacture top surfaces of appurtenant structures with 6 mm 1/4 inch steel
conforming to ASTM A 242/A 242M raised pattern floor plate in a manner
similar to that specified herein including soffit and fascia dimensions.
Aluminum casing materials shall conform to ASTM B 209M ASTM B 209.
2.4.2
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NOTE: For operating temperature range of 94 to 260
degrees C 201 to 500 degrees F use minimum thickness
of 115 mm 4 1/2 inches. For operating temperatures
261 degrees C 501 degrees F and above use minimum
thickness of 140 mm 5 1/2 inches.
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Insulate the precipitator housing, penthouse, and hoppers with ASTM C 612
SECTION 15862N
Page 34
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