Section
10 Flat plates and ends of vertical boilers
10.1 Tube plates of vertical boilers
10.1.1 Where
vertical boilers have a nest or nests of horizontal tubes, so that
there is direct tension on the tube plates due to the vertical load
on the boiler ends or to their acting as horizontal ties across the
shell, the thickness of the tube plates in way of the outer rows of
tubes is to be determined by the following formula:
|
|
= |
where t, c and p are as defined in Pt 5, Ch 10, 1.2 Definition of symbols
|
|
D
|
= |
twice
the radial distance of the centre of the outer row of tube holes from
the axis of the shell, in mm |
|
J
|
= |
efficiency
of ligaments between tube holes in the outer vertical rows (expressed
as a fraction) |
| = |
|
|
R
20
|
= |
specified minimum tensile strength of tube plate, in N/mm2
|
where
|
d
|
= |
diameter
of tube holes, in mm |
|
s
|
= |
vertical
pitch of tubes, in mm. |
10.1.3 Where
the vertical height of the tube plates between the top and bottom
shelves exceeds 0,65 times the internal diameter of the boiler, the
staying of the tube plates, and the scantlings of the tube plates
and shell plates to which the sides of the tube plates are connected,
will require to be specially considered. It is recommended, however,
that for this type of boiler the vertical height of the tube plates
between the top and bottom shelves should not exceed 1,25 times the
internal diameter of the boiler.
10.2 Horizontal shelves of tube plates forming part of the shell
10.2.1 For
vertical boilers of the type referred to in Pt 5, Ch 10, 10.1 Tube plates of vertical boilers, in order to withstand vertical
load due to pressure on the boiler ends, the horizontal shelves of
the tube plates are to be supported by gussets in accordance with
the following formula:
where
|
p
|
= |
design pressure, in MPa |
|
t
|
= |
thickness
of the tube plate, in mm |
|
A
|
= |
maximum
horizontal dimension of the shelf from the inside of the shell plate
to the outside of the tube plate, in mm |
|
D
i
|
= |
inside diameter of the boiler, in mm. |
10.2.2 For
the combustion chamber tube plate the minimum number of gussets is
to be:
1 gusset, where C exceeds 255 000
2
gussets, where C exceeds 350 000
3 gussets
where C exceeds 420 000.
10.2.3 For
the smokebox tube plate the minimum number of gussets is to be:
1 gusset where C exceeds 255 000
2
gussets where C exceeds 470 000.
10.2.4 The
shell plates to which the sides of the tube plates are connected are
to be not less than 1,6 mm thicker than is required by the formula
applicable to shell plates with continuous circularity, and where
gussets or other stays are not fitted to the shelves, the strength
of the parts of the circumferential seams at the top and bottom of
these plates from the outside of one tube plate to the outside of
the other, is to be sufficient to withstand the whole load on the
boiler end with a factor of safety of not less than 4,5 related to R
20 (where R
20 is the specified
minimum tensile strength of the shell plates, in N/mm2).
10.3 Dished and flanged ends for vertical boilers
10.3.1 The
minimum thickness, t, of dished and flanged ends for
vertical boilers which are subject to pressure on the concave side
and are supported by central uptakes is to be determined by the following
formula:
10.3.2 The
inside radius of curvature, R
i, of the end
plate is to be not greater than the external diameter of the cylinder
to which it is attached.
10.3.3 The
inside knuckle radius, r
i
, see
Figure 10.4.2 Typical dished ends(a), of the arc joining
the cylindrical flange to the spherical surface of the end is to be
not less than four times the thickness of the end plate, and in no
case less than 65 mm.
10.3.4 The
inside radius of curvature of flange to uptake is to be not less than
twice the thickness of the end plate, and in no case less than 25
mm.
10.3.5 If
the dished end has a manhole, the opening is to be strengthened by
flanging. The total depth, H, of the flange, measured
from the outer surface of the plate on the minor axis, is to be not
less than
where
|
t
|
= |
thickness
of the flange, in mm |
|
H
|
= |
depth
of flange, in mm |
|
W
|
= |
minor
axis of the manhole, in mm. |
10.4 Flat crowns of vertical boilers
10.4.1 The
minimum thickness of flat crown plates of vertical boilers is to be
determined as in Pt 5, Ch 10, 9.1 Stayed flat surfaces; d and C are defined as follows:
- Where the crown is supported by an uptake only,
|
d
|
= |
diameter
of the largest circle which can be drawn through at least three points
of support, in mm |
|
C
|
= |
the
mean of the values for the respective points of support through which
the circle passes. |
|