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  Reg. 370

Flexibility

a)

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.
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