practice recommendations and requirements of SMACNA Rectangle Duct Const
and SMACNA Rnd Duct Const,
for Class [IV] [_____] duct.
2.10.2
Protective Coating
Provide [_____] [and] [_____] protective coatings as specified under
"Protective Coating Materials" subparagraph of paragraph entitled
interior of duct [and related fan] surfaces. Coat exterior duct [and
related fan] surfaces with same protective coating as specified for
exterior surfaces [primed with] [inorganic zinc coating] [_____].
[Exterior fan surfaces shall be finished [protectively coated] [primed] [as
specified under paragraph, "_____".]] [Field finish exterior surfaces
which have only been primed, as specified in Section 09900 PAINTS AND
COATINGS.]
2.10.3
Fabrication of Protectively Coated Ductwork
Construct protectively coated ductwork for corrosive fume and vapor exhaust
in accordance with SMACNA Rectangle Duct Const and SMACNA Rnd Duct Const
and as specified herein. Provide indicated sizes, lengths and
configuration without deviation, unless otherwise approved. Spiral welded
duct is prohibited. Install ductwork to be water washable, watertight,
self-draining, and airtight [as defined under paragraph entitled "Ductwork
Structural Integrity and Leakage Testing," in this section]. Provide
necessary reinforcements, bracing supports, framing, gasketing, and
drainage provisions, and fastening to guarantee rigid construction and
freedom from vibration, airflow induced motion, and excessive deflection.
Rigid construction is required to prevent damage to or failure of
protective coating during construction, transport, erection, and on-off
system operation. Only companion angle flanged joints shall be permitted.
Weld ducting and fittings seams. Avoid seams in bottom 80 mm 3 inchesof
ducting and in corners wherever practical by bending of corners and
arranging seams high in the side sheets or top sheet. Cracks, laps, sharp
inside corners, sharp sheared edges, weld "icicles," flux, pits, weld
spatter, burrs, and similar defects which contribute to coating
discontinuities shall be eliminated by the following: a) welding
continuously, b) grinding of metal flush with surface or to 0.8 mm 1/32
inch radius or to maximum radius permitted by thinner metals, c) Utilizing
other fabrication techniques and subsequent surface preparation abrasive
blasting. Removed from the job site for repair rejected ducting not
conforming to these requirements and which exhibit coating thickness
deficiency. Welding shall conform to requirements specified herein.
Continuously weld companion flange angles to the inside of the duct and
intermittently weld with 25 mm one inch welds every 100 mm 4 inches on
outside of duct. Intermittently weld girth and transverse reinforcements
to duct surface for 25 mm one inch on 152 mm 6 inch centers or spot welded
on 100 mm 4 inch centers. Weld and grind flange and reinforcement angles
at corners or ends to form continuous frames. Provide flanges at
[branches,] [hoods,] [equipment] [and] [enclosure connections,] where
necessary for ease of access to equipment or maintenance disassembly, and
where indicated. Limit duct lengths in accordance with size, to permit
complete and ready access for welding, grinding, blasting, coating, coating
continuity checking and testing, and visual inspection during fabrication
and immediately prior to erection.
2.10.4
Radius Elbows
Fabricated radius elbows from butt welded specified piece gore sections or
SECTION 15801N
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