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Reg. 518

STANDARD CONDITIONS FOR THE DESIGN AND CONSTRUCTION OF ECONOMISER, FEED PIPES, FEED HEATERS AND OTHER SIMILAR VESSELS

JOINT BOLTS AND STUDS

Joint bolts, studs and flanges

a)

The maximum working pressure for the bolts shall be determined by the following formula:-

W.P. = N x C ( D - 1.28 Eqn.(121)
A n

N = No. of bolts securing the parts.
n = No. of screw threads per inch.
D = Bolt Diameter in inches measured over the threads.
A = The area exposed to pressure which is assumed to be bounded by a line midway between the pitch line of the bolts and the inner edge of the flange where flat joints are used with joint rings. Where conical joints are used with joint rings of curvilinear cross-section, the area exposed to pressure shall be assumed to extend to the root of the thread where the tube ends are screwed, or to a corresponding boundary if the flanges are attached by other means.

C = 4,700 for steel bolts or studs of 28 tons/sq. in. minimum ultimate tensile stress where the diameter over thread in less than ¾ inch.

C = 5,100 for steel bolts or studs of 30 tons/sq. in. minimum ultimate tensile where the diameter over thread is less than ¾ inch.

C = 5,600 for steel bolts or studs of 35 tons/sq. in. minimum ultimate tensile where the diameter over thread is less than ¾ inch.

C = 5,600 for steel bolts or studs of 28 tons/sq. in. minimum ultimate tensile where the diameter over thread is less than ¾ inch and not greater than 7/8 inch.

C = 7,000 for steel bolts or studs of 28 tons/sq. in. minimum ultimate tensile where the diameter over thread is greater than 7/8 inch.

Where the bolts or studs used have a tensile strength exceeding 32 tons sq. in., a plate shall be permanently fixed to the economiser structure in a prominent position drawing attention to this fact in case replacements of bolts or studs are necessary. In no case shall the nuts be exposed to the action of the flue gases.
b) The thickness of each flange shall be not less than that given by the following equation:-

                          -----------------

P.D.[D1-D]

                    t = ------------------

                                    2


Where ,

t=Thickness of flange in thirty-second of an inch.
P=Working pressure, in pounds per square inch (gauge).
D=Outside diameter of the tube in inches.
D1=Pitch circle diameter of bolts or studs in inches. Provided that such flange is cast integral with the body and with appropriate internal corner radius.

In no case, however, shall the thickness of a flange be less than 24 thirty-seconds of an inch.
 
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