The amount of support in relief of the stays which
may be attributed to the shell, furnaces or flues to
which flat plates are attached, shall not exceed that
determined by the following formulae:-
Width of margin in inches =
t is plate thickness in thirty seconds of an inch.
W.P. is working pressure in pounds per square inch.
C=3.47 for plates exposed to flame.
C=3.70 for plates not exposed to flame.
Where the plates are flanged, the margin shall be measured
from the commencement of curvature of flanging, or from
a line 3 ½ times the thickness of the plate measured
from the outside of the plate, whichever is nearer to
the flange. Where the flat plate is not flanged for attachment
to the shell or flue tubes and is welded as shown in figure
XII/12 or XII/16 the width of the margin shall be measured
from the inside of the shell or the outside of the flue
tube, whichever is applicable.
In no case, however, shall the diameter D of the circle
forming the boundary of the margin supported by the uptake
of a vertical boiler be greater than that found by the
= / 5000A
A is cross sectional area of the uptake tube in square
W.P. is working pressure in pounds per square inch,
d is external diameter of uptake in inches.