a)

For unstayed ends of shells and tops of vertical boilers
and the like boiler parts, when dished to partial spherical
form the maximum working pressure shall be determined
by the following formula:
WP
= 
15
x S X (t1) 
Equation XII/7

R 
WP is the working pressure in pounds per square inch.
t is thickness of the end plate in thirty seconds of an
inch but in no case this shall be less than the thickness
of the shell to which it is attached.
R is the inner radius of curvture of the end in inches,
which shall not exceed the external diameter of the shell
to which it is attached.
S is the minimum tensile breaking strength of plate in
tons per square inch, or whatever is allowed for it.

b) 
The inside radius
to which a crown plate is dished shall be not greater
than the external diameter of the cylinder to which it
is attached. 
c) 
The inside radius
of curvature of the flanges to the shell shall be not
less than 4 times the thickness of the crown plate and
in no case less than 2 ½ inches. 
d) 
The inside radius
of curvature of flanges to uptakes shall be not less than
twice the thickness of the crown plate and in no case
less than 1 inch. 
e) 
When the end has
a manhole in it (t5), shall be substituted for (t 1)
in the formula. 
f) 
The total depth
of flange of manhole from the outer surface in inches
measured on the minor axis shall be at least equal to
ÖT
X W depth of flange in inches 
Equation XII/8 
where T is the thickness of the plate in inches and W
is the minor axis of the hole in inches. 
g) 
The depth of the
crown plate opening from the commencement of the curvature
of the flanging radius shall be not less than twice the
plate thickness with a minimum of one inch. 