

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 
)² 
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 crosssection, 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:

Ö
P.D.[D1D]
t = 
2

Where ,
t=Thickness of flange in thirtysecond 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 thirtyseconds of an inch. 

