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Reg. 568, Reg. 569, Reg. 570

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.




Reg. 569

Hemispherical crowns

 The maximum working pressure for hemispherical crowns subjected to internal pressure shall be determined by the following formula:-

WP = (t-2) S x C Equation XII/9
R

Where,

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 square inch.
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 563.

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.




Reg. 570

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.
 
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