|
PIPING DESIGN AND
PRESSURE ESTIMATION
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:
PD
Wall Thickness
T =
----------------------- +C
2C + 2YP
2S (T-C)
Internal Pressure
P =
-----------------------
D - 2Y (T-C)
Where
T =
design thickness of the pipe (122 % 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 1050oF
0.5 for 1100oF
0.7 for 1150oF
For non ferrous metals-
0.4 up to and including 900oF
Note:
Conversion Factors
1 Bar
= 14.5 psi
1 MPa =
10 Bars = 145 psi
1 inch =
25.4mm
oF
= (oC
x 9/5) + 32
For
allowable stress, S
|
Temp.
(oF)
|
Grade
|
|
304L
|
304
|
316L
|
316
|
321
|
|
(Psi)
|
(304L
value multiplied by)
|
|
Upto
300oF
400 oF
500 oF
600 oF
|
14
200
13 400
12 500
11 850
|
x
1.20
x 1.19
x 1.18
x 1.18
|
x
1.00
x 0.98
x 0.98
x 0.97
|
x
1.20
x 1.22
x 1.22
x 1.22
|
x
1.20
x 1.18
x 1.17
x 1.17
|
|
