| 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
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 |
|
| 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.
|
