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Reg. 575, Reg. 576, Reg. 577 a, Reg. 577
b
Flat crown plates for vertical boilers
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i)
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Flat
crown plates shall be supported by the uptake and/ or
bar stays . |
| ii) |
The
inside radius of curvature of the flange to the shell
or fire box shall be not less than four times the thickness
of the plate and in no case less than 63 mm where the
plate is flanged for attachment to the uptake, the inside
radius of curvature of the flange shall be not less than
twice the thickness of the plate and in no case less than
25 mm. |
| iii) |
The
thickness of flat crown plates shall be determined in
accordance with Regulation
574.
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Reg. 576
Wide water spaces between and around tube nests
The
thickness of plate at wide water spaces shall be calculated
as per regulation 574 taking d =
(A² + B²)1/2
Where,
A - is width of the wide water space between the tube
nests in mm measured from centre to centre of the tubes;
and
B - is pitch of the tubes in the boundary rows of the
wide water space in mm.
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Reg. 577
Flat tube plates
and tube nests
a) Stay tubes and plain tubes
| (i) |
Stay tubes are tubes having a weld depth equal to the
nominal tube thickness plus 3 mm as shown typically in
figures XII/68A(i) to
(iv). These stay tubes are not required
within tube nests except when the tube nests comprise
tubes which are expanded only as shown typically in figure
XII/67A (iii). |
| (ii) |
If
tube nests comprise plain tubes which are expanded and
beaded, expanded and belled as shown typically in figure
XII/67A(iv) or expanded and welded (as shown typically
in Figs. XII/67A
(i) and (ii) ), welded stay tubes (as
shown typically in Figs. XII/67A
(i) to
(iv) shall be used in boundary
rows in sufficient numbers to carry the flat plate loadings
outside the tube area. |
| (iii) |
For
plain tube and stay tubes exposed to flame or gas temperatures
exceeding 600°C, the ends of welded tubes shall be
dressed flush with the welds and the ends of the expended
tubes shall be as shown in figures XII/67A(iii)
and (iv).
If not so exposed, the ends of welded tubes shall extended
a maximum of 10 mm beyond the weld or, in the case of
expanded tubes, the tubes shall project beyond the tube
plate up to a maximum of 15 mm. |
| (iv) |
Each
stay tube shall be designed to carry its due proportion
for the load on the plates which it supports. The thickness
of stay tubes welded into tube plates shall be such that
the axial stress on the thinnest part of the tube does
not exceed 70 N/mm².
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Reg. 577 b
Parts of flat plates within tube nests
| If stay tubes are
used within tubes nests, the thickness of the tube plate
shall be calculated in accordance with regulation
574. |
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