About Central Boilers Board •Contents Chapter Wise • Contents Regulation WiseIndian Boilers Act 1923
Reg. 350

Steel Pipes

The maximum working pressure allowed on steel pipes shall be determined by the following formula:
a)

Where the outside diameter is the basis for calculation.

 W. P. = 2 f e (t - c) Equation 91 D - t + c
b) Where the inside diameter is the basis for calculation.,

 W. P. = 2 f e (t - c) Equation 91A d + t - c

Where

t = Minimum thickness
W. P. = Maximum working pressure
f = Allowable stress as provided under regulation 271
D = Outside diameter of pipe
d = Inside diameter of pipe
e = Efficiency factor
= 1.0 for seamless and for electric resistance welded steel pipes and for electric fusion welded steel pipes complying with the requirements of Chapter II in which the weld is fully radiographed or ultrasonically tested.
= 0.95 for electric fusion welded steel pipes complying with the requirements of Chapter II,
= 0.90 for welded steel pipes for values of t up to and including 22mm.
= 0.85 for welded steel pipes for values of t over 22mm and up to and including 29mm.
= 0.80 for welded steel pipes for values of t over 29 mm.

C = 0.75mm.

Note: In case Sc values are not available in Material Standard and such materials are known to have been used in boilers in India or abroad, then for such materials, the allowable stress may be taken as the lower of

 Et or Sr 1.5 1.5

Carbon Steel

Seamless, hydraulic
lap welded and
The lower value obtained
on the following basis from
Electric resistance welded for temperatures up to and including

 350°C (662°F) T.S or Et 2.7 1.5
For temperatures above 454°(850°F)
Molybdenum steel seamless
 Et or Sr or Sc 1.5 1.5
Chromium Molybdenum Steel seamless

where, T. S. = Minimum Tensile strength at 20°C(68°F)
Et = Yield point (0.2% proff stress) at the temperature t.
Sr = The average stress to produce rupture in 100,000 hours and in no case,                             more than 1.33 times the lowest stress to produce rupture.
Sc = The average stress to produce an elongation of 1% (creep) in 100,000 hours.

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