About Central Boilers Board •Contents Chapter Wise • Contents Regulation WiseIndian Boilers Act 1923
Reg. 175, Reg. 176
REGULATIONS FOR DETERMINING THE WORKING PRESSURE TO BE ALLOWED ON VARIOUS PARTS OF BOILERS OTHER THAN FUSION WELDED AND SEAMLESS FORGED DRUMS

Reg. 175

Maximum pressure

The maximum pressure at which a boiler may be used shall be determined in accordance with the provisions of this Chapter. The regulations in this chapter refer to material subjected to steam temperature not exceeding 500° F.

Reg. 176
SHELLS

Formula for Working Pressure of Shell

a) For cylindrical shells, barrels, steam and water drums, and domes of boilers for maximum working pressure per square inch to be allowed shall be calculated from the following formula :-

(Note - Where parts of drums of water tube boilers are perforated for tubes, the working pressure shall be calculated by equation (53) under 'Tube Plates')

 W. P .= (t - 2) x S x J Eqn. (1) C x D

Where
W. P. = the working pressure in lbs. per square inch;

t = the thickness of shell plates in 32nds of an inch;

S = the minimum tensile breaking strength of the shell plates in tons per square inch or whatever strength is allowed under Regulation 5;

J = the percentage of strength of the longitudinal seams of shell or of a line of holes in the shell for stays, or rivets, or of an opening in the shell not fully compensated, whichever is least calculated by the methods hereafter described;

C is a co-efficient as follows :-

2.75 when the longitudinal seams are made with double butt straps and when small shells are formed from solid rolled sections.

2.83 when the longitudinal seams are made with lap joints and are treble riveted.

2.9 when the longitudinal seams are made with lap joints and are double riveted

3.0 when the longitudinal seams are welded and are fitted with a single butt strap.

3.3 when the longitudinal seams are made with lap joints and are single riveted.

D = the inside diameter of the outer strake of plating of the cylindrical shell measured in inches.

b)

c)

d)

The factor of Safety shall in no case be less than 4.

The actual factor of Safety in each case may be found from the equation ;

 F = 1.4 x C x t t - 2

With the best form of joint and least co-efficient (c) the Factor of Safety for shell plates, 1/4 inch to 1-3/4 inches in thickness varies from 5.13 to 3.99.

An addition of 10 per cent, shall be made to the appropriate co-efficient for shells of boilers in which the longitudinal seams are lap jointed and are not accessible to close visual inspection and for shell plates of externally fired boilers exposed to the direct impact of furnace flame; provided that this addition shall not apply to the steam and water drums of water tube boilers where the drums are not close to the fire-grate and there are tubes between the fire-grate and the drum.

The above co-efficient are standards and shall be used only for boiler open to inspection by an inspecting officer during the whole period of construction and which are certified by him as having constructed in accordance with the standard condition laid down in these Regulations

 About Central Boiler Board Foreword • List of Amendments Ibr Forms • Home • Search • Help • Contact Us