Reg. 568, Reg. 569, Reg.
Dished ends subject to external pressure
In the case of unstayed dished ends for the coefficient
15 in Equation XII/7, the coefficient 12 shall be substituted,
and R shall be the outer radius of the curvature of
plate, which shall not exceed the external diameter
of the shell to which it is attached.
For plates exposed to furnace-flame the coefficient
shall be 10.5. In no case shall
R/t exceed 2.75.
The inside radius of curvature at the flange shall be
not less than 4 times the thickness of the end plate
and in no case less than 2 ½ inches.
The inside radius of the curvature of the flange to
uptake shall be not less than twice the thickness of
the crown plate and in no case less than one inch.
| The maximum working
pressure for hemispherical crowns subjected to internal
pressure shall be determined by the following formula:-
S x C
t is thickness of plate in thirty-seconds of an inch.
WP is the working pressure in pounds per square inch.
R is inner radius of curvature in inches.
S is minimum tensile strength of the plate in tons per
C is a constant, as given below.
In no case, however, shall the factor of safety of the
crown plate be less than 4 nor the plate thickness be
less than specified in Table given under Regulation
C=32 where Class I requirements are complied with.
C=27 where Class II requirements are complied with.
C=23 for Class III boilers when stress relieved.
C=21 for Class III boilers when not stress relieved.
Manholes and other openings in shells
|Manholes and other
openings in shells shall be placed as far as possible
from any seam. Wherever practicable oval openings shall
be arranged with the minor axis parallel with the longitudinal
centre line of the boiler. In no case shall the circumferential
length of any opening exceed twice the longitudinal width
of the opening.