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Reg. 193
FLAT PLATES
Flat plates supported by solid screwed stays, marginal seams
or flanges
| a) |
For plain flat plates supported
by solid screwed stays or riveted marginal seams or flanges,
the maximum working pressure shall be as follows : -
| W.P. = |
C ( t
- 1 )2 |
Eqn.(28) |
| A2 +
B2 |
In this formula and in those following in the succeeding
regulations relating to "Flat Plates" unless
otherwise specified
W. P. is the working pressure in lbs. per square inch.
t is the thickness of the flat plat in 32nds of an inch,
t1 is the thickness of the washers, strip or dublings
employed in 32nds of an inch ,
A is the horizontal pitch of stays in inches,
B is the vertical pitch of the stays in inches,
C is a co-efficient which varies in value with method
of vexing the stays and nature of the support.
Where the plates are exposed to the direct impact of the
flame the following of C shall be reduced 12-1/2 per cent-
C = 60 for stays screwed into the plate with their ends
riveted over,
C = 90 for stays screwed into the plate and and fitted
with nuts on the outside,
C = 100 for stays passed through the plate and fitted
with nuts inside and outside
C = 110 for a riveted seam or flange, in the flat plate
securing it to the shell side plate, end plate, furnace
or uptake.
Where portions of plate are supported by stays or riveted
seams or flanges having various values of support, the
value of C, shall be taken as the mean of the points of
support concerned.
The support of a riveted seam shall be assumed to be at
the line through the centres of rivets in the nearest
row and of a flange at the commencement of curvature.
In the latter case, if the inner radius of curvature of
the flange exceeds 2-1/2 times of the thickness of the
plate, the support shall be assumed to be at a distance
of 2-1/2 times the thickness of the plate from the inner
side of the flange. |
| b) |
For portions of plate where
the stays are irregularly pitched D2 shall be used instead
of A2 + B2, D being the diameter in inches of the largest
circle which can be drawn passing through not less than
three points of support, viz., the centres of stay or
rivets or the commencement of the curvature of flanging
whichever is applicable. |
| c) |
For the tops and sides of
combustion chambers and fireboxes the distance between
the rows of stays nearest to the back tube plate, or the
back or firehole plate respectively, and the commencement
of curvature of these plates at their flanges shall not
be greater than the maximum pitch of the stays. |
| d) |
For the tops of combustion
chambers and fireboxes where they are joined to the sides
by curved portions, if the outer radius of the curved
portion is less than half the allowable distance between
the girders, the distance between the first girder and
the inner surface of the side plates shall not exceed
the allowable distance between the girders. If the radius
of curvature is greater than half the allowable distance
between the girders, the width of the flat portion measured
from the centre of the girder shall not be more than half
the allowable distance between the girders. |
| e) |
Where stay tubes are not fitted
in nest of tubes, as in tube plates of locotype boilers,
and parts of plate outside the space occupied by tubes
are supported, in accordance with Regulation
212 (b), by screwed stays each stay in the row nearest
the tube shall be of sufficient strength to support the
plate up to the edges of the tube holes in addition to
its share of the plate on the opposite side of the line
of stays.
The working pressure for the plate between tubes and stays
shall be determined by Eqn.(28). A being the horizontal
pitch of the stays in the nearest row, B twice the distance
between the centre line of stays and a line touching the
tubes opposite them and C the co-efficient appropriate
to the kind of stay. |
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