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Reg. 170
MANHOLES, MUDHOLES, ETC.
Compensation for cutting large holes in Shell Type Boilers
| a) |
Where holes are cut in the
cylindrical shell for the purpose of attaching a seating
of frame or door, compensation shall be provided such
that the added sectional area, including parts of the
frame within 4 inches of the shell and excluding rivet
holes, shall be not less than the sectional area of the
plate removed which shall be the product of the diameter
of the opening and the calculated thickness of the plate
as found by Equation 1. Where holes are cut in the cylindrical
shell for the purpose of fixing seating for mountings
and the diameter of the holes is greater than 2½
times the thickness of the shell plate plus 2¾
inches, compensation shall be provided. Where a large
opening is cut in a cylindrical shell to receive another
part of the structure, the sides where cut away shall
be efficiently cross-stayed or strengthened in some other
effective manner. |
| b) |
Riveted construction.- Where
frames, pads or branches are secured by riveting on shell
for fixing of mountings or other pressure parts, the sectional
area to be compensated shall be determined as follows:-
(See Figure 25A).
| i) |
The cross-sectional area
of the frame or pad excluding rivet holes, or in
the case of a branch the cross-sectional area of
the wall of the branch and flange, excluding rivet
holes, minus the sectional area of a branch of the
same bore having thickness calculated by equation
1 for the same design pressure, using C=2.75, J=65
when butt welded, and J=95 when seamless, plus the
thickness required to withstand external loads.
The area shall be measured within the limit specified
in Figure
25-A.
Due allowance shall be made in case where the material
used for the branch and/or compensating ring differs
from that of the plate to which it is attached.
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| ii) |
The area obtained by
multiplying the difference between the actual shell
thickness and the calculated thickness, by a length
2(3 inches + Ts-d)
Ts = Thickness of the shell plate in inches.
d = diameter of rivet hole in inches. |
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In cases where the sum of (i) and (ii) is less than the sectional
area to be compensated, a compensating plate shall be fitted
having a total net cross-sectional area equal to the amount
of the deficit. |
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