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Reg. 582, Reg. 583, Reg. 584
Compression of tube plates
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a)
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For
fire-box or combustion chamber tube plates which are subject
to compression due to the pressure on the roof plate,
the maximum working pressure shall be:
| WP = |
C x (P-D) x t |
Equation XII/17 |
| L x P |
t is thickness of the tube plate in thirty seconds of
an inch.
P is pitch of the tubes in inches, measured horizontally
where the tubes are chain pitched or diagonally where
the tubes are zig zag pitched and the diagonal pitch is
less than the horizontal.
D is internal diameter of the plain tubes in inches.
L is internal length of the fire-box or combusion chamber
in inches measured at top between tube plate and firehole
plate or back plate, or between tube plates in double
ended boilers with combustion chambers common to two opposite
furnaces.
C = 875.
Provided that the above formula shall not apply in the
cases of fireboxes where the girders do not rest on the
tube plate, or where the roof plate is stayed direct to
the outer shell or to girders supported by the shell. |
| b) |
Where
girders rest on the side plates or the roof plate is so
formed that the load is carried both by side and end plates,
the compressive stress on the plate shall not in either
case exceed 14,000 pounds per square inch. |
Reg. 583
Girders for fire-box and combustion chamber crowns
| a) |
For girders
supporting crown plates of rectangular fire-boxes, where
the ends of the girders are supported by the vertical
end or side plates, their proportions shall be calculated
by the following formula:
| WP= |
CST d² |
Equation XII/18 |
| L² Y |
Where,
WP is Working pressure in pounds per square inch,
S is Minimum tensile stress of the material in tons per
square inch,
T is Total thickness of the stay in thirty seconds of
an inch.
d is Depth of the girder stay in inches,
L is Length of girder stay in inches measured between
the inside of the tube plate and the fire-hole plate, or
between the inside of the side plates, according to the
method of support.
Y is Pitch of girder stays in inches.
C = 22 for steel plates or steel forgings,
= 19 for steel castings. |
| b) |
Where
girders are welded to the crown plate the dimensions
of the welds shall be such that the stress calculated
on an area equal to the sum of the effective lengths of
the welds attaching each girder multiplied by the effective
throat thickness shall not exceed 7,500 pounds per square
inch multiplied by the appropriate weld factor in Table
XII/7, (“effective length” and “effective
throat thickness” are defined in Regulation
591). The load on the welds shall be taken as that
due to the design pressure acting on the area LY; L and
Y being as defined in Regulation
583. |
Reg. 584
Girder sling stays
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slung girders the proportion of slings, links, pins and
connections to the shell shall be sufficient to carry
the whole load that would otherwise be carried on the
toes of the girders and for any of the above parts in
tension a stress of 9,000 pounds per square inch of net
section, and for parts in shear a stress of 8,000 pounds
per square inch of net section shall not be exceeded.
In the case of parts in double shear, the net area of
the section should be taken as 1.875 times the single
section. |
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