Piping Design and Pressure Estimation

Piping Design and Pressure Estimation 

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The rules for designing a piping system are given in various national codes, eg. ANSI B31, BS 3351, ASME Section 3.

The code specifications which are applicable will be determined by the general service for the piping system and will dictate the minimum requirements in respect of dimensional standards, materials, etc.

Flow rate, pressure drop, external forces, thermal stresses and deadweight are some of the parameters to be taken into account.

Two useful computations which can be used for seamless and welded pipe, but which are not substitutes for design codes are:

piping design

Where :

T = design thickness of the pipe (12 1/2% less than the nominal wall thickness of any given Pipe size), inches
P =   internal design pressure,  PSIG
D = outside diameter of pipe, inches
S = allowable stress of materials at service temperature, PSI
C = allowance for mechanical and corrosion, inches (zero for our calculations)
Y = a coefficient having values as follows:
For austenitic stainless steels
0.4 up to and including 1 050°F
0.5 for 1 100°F
0.7 for 1 150°F
For non ferrous metals –
0.4 up to and including 900°F

Note: Conversion Factors
1 Bar    =     14.5psi
1 inch  =     25.4
1 MPa  =     10 Bars  =   145psi
0F        =     (°C x 9/5) + 32

For allowable stress, S

Temp
◦F
GRADE
304L 304 316L 316 321
Psi (304L value multiplied by)

    Up to 300 ◦F

14 200 x 1.20 x 1.00 x 1.20 x 1.20
400 ◦F 13 400 x 1.19 x 0.98 x 1.22 x 1.18
500 ◦F 12 500 x 1.18 x 0.98 x 1.22 x 1.17
600 ◦F 11 850 x 1.18 x 0.97 x 1.22 x 1.17

working pressures

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