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a)
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The pipes shall be arranged so that the system is sufficiently
flexible to absorb the whole of their expansion and
the imposed movement of the connected equipment without
the actual expansion stress (SE) exceeding the allowable
stress range (SA) as is determined from the following
equation:-
SA = f (1.25 SC + 0.25 SH )
where,
SC = Basic material allowable stress at the minimum
(Cold) temperature.
SH = Basic material allowable stress at maximum (hot)
temperature.
SE = Actual calculated expansion stress obtained from
the stress analysis .
f = Stress range reduction factor for cyclic conditions
for total number N of full temperature cycles over the
total number of years during which the systems is expected
to be in operation as given in table below:-
Table:- Stress range reduction factors:
| N |
F |
| 7,000 and less |
1.0 |
| 7,000 - 14,000 |
0.9 |
| 14,000 - 22,000 |
0.8 |
| 22,000 - 45,000 |
0.7 |
| 45,000 - 100,000 |
0.6 |
| 100,000 and above |
0.5 |
Note 1: Values of SC and SH shall be guaranteed
by the manufacturer of steel from which pipes are made
and furnished to the pipe makers/Inspecting Authority
until such time such values of SC & SH are incorporated
in the Regulations.
Note 2: In case of imported pipes conforming to
a recognised foreign standard or code the values of SC
and SH may be taken from the table of allowable stress
as given in that code or the values may be determined
on the basis given in that code.
Note 3: The sum of the longitudinal stress due
to pressure, weight and other sustained load including
bending stresses caused by external loads shall not exceed
the allowable stress in the hot conditions (SH) where
the sum of these stress is less than SH, the difference
between SH and this sum may be added to the term 0.25
SH in the above formula for determining the allowable
stress range SA.
Note 4: Calculation of the expansion stress, SE
shall be based on modulus of elasticity at room temperature. |
