2.2.2
Construction
2.2.2.1
Boiler Drums
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NOTE: Boilers 11 1/4 kg of steam per second 90,000
pounds of steam per hour or more should have a steam
drum of not less than 1372 mm 54 inches in diameter
and a lower drum of not less than 1067 mm 42 inches
in diameter.
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Drums shall be steel plate, fusion welded in conformance with the ASME BPVC
SEC I. The manufacturer shall determine the inside diameter and overall
length of each drum except that the steam drum shall be sized sufficiently
large to contain the steam-water separating equipment, to prevent excessive
rise of water due to sudden change in steam demand, and to allow for ready
access into the drum. The steam drum shall be at least [_____] mm inches
internal diameter. The lower drum shall be at least [_____] mm inches
internal diameter. Provide each drum with an elliptical manhole at each
end not less than 300 by 400 mm 12 by 16 inches, with hinged manhole cover,
yoke and gaskets and machined to fit manhole flange of head. Provide flat
bar ring of not less than 10 gage steel plate welded to the exterior of the
drum heads around the manholes for protection of the drum head insulation.
Rings shall be continuous and shape shall conform to the general outline of
the manhole opening. Groove the tube holes in the drums for maximum
holding power. Fusion weld the longitudinal seams in drums and the
circumferential joints between heads and shells. Remove excess welding
material and clean drum surface.
Relieve stresses caused by welding by
heat treatment in annealing furnaces, and X-ray the seams to ensure
complete and proper welding. Drum variation shall not exceed one percent
between maximum and minimum diameters at any section and when necessary,
reheat, reroll or reform drums to meet this requirement.
a.
No part of the boiler drum or header surface shall be directly
exposed to furnace radiation unless it is adequately protected by
a water screen in such a manner that no part of the exposed drum
or header surface shall be more than 50 mm 2 inches from the
nearest water tube.
b.
Fit the steam outlet drum of the boiler with easily removable
efficient dry pipe, special baffle, or other separating device so
that the steam delivered to the boiler header shall have not more
than 1.0 ppm of total solids at maximum continuous load, and
during change of load from 50 percent to 100 percent of continuous
rated capacity within a three minute period, provided that the
total solids concentration in the boiler water does not exceed
3500 parts per million, the total alkalinity concentration does
not exceed 700 parts per million, and no organic matter is present.
c.
Nozzles for safety valves, main steam outlet, feed and blowdown
lines, shall be forged steel, straight neck type, flanged and
fusion welded to drums. Weld threaded connections in the steam
drum for the feed water regulator, continuous blowdown, vent gage,
and chemical feed lines.
d.
Provide steam drum with internals for continuous blowdown, running
the length of the steam drum at the point of highest concentration
of dissolved solids, and an internal distribution pipe for
SECTION 15502N
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