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Reg. 582, Reg. 583, Reg. 584

Compression of tube plates

 

a)

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


For 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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