h a n g e Vi h a n g e Vi
XC e XC e
F- w F- w
PD
PD
er
er
!
!
W
W
O
O
N
N
y
NORSOK standard P-001 Edition 5, Sep. 2006
y
bu
bu
to
to
k
k
lic
lic
C
C
w
w
m
m
w w
w
w
o
o
.d o .c .d o .c
c u -tr a c k Table 3 - Flow capacity - Near horizontal pipes c u -tr a c k
Diameter Liquid flow capacity (see NOTE)
mm (in) m3/h
Slope 1:50 Slope 1:100
50 (2) 3,7 2,6
100 (4) 24 17
150 (6) 70 49
200 (8) 150 106
250 (10) 271 192
300 (12) 441 312
350 (14) 665 471
400 (16) 950 672
NOTE According to the Manning formula (see Finnemore and Franzini, “Fluid Mechanics with Engineering Applications”, McGraw-Hill,
New York, 10. ed. 2002) a pipe “filling degree” of 75 % is assumed.
The liquid in the entrance part of a near horizontal pipe normally need some acceleration distance to reach
fully established velocity. To reduce the entrance pressure loss, the inlet section should have increased
diameter compared to Table 3. For the first ten pipe diameter length, the next larger pipe diameter in Table 3
should be selected ending with an eccentric reducer.
Vertical lines
Vertical gravity lines with or without submerged outlets (e.g. so-called “dump caissons”) shall be designed
such that the Froude number is less than 0,3. This is to avoid air entrainment and ensure undisturbed flow
without pulsations.
V
Froude number = (1)
D× g
where
V is the velocity assuming full pipe in m/s
D is the pipe inner diameter in m
g is the gravity constant in m/s2
A vent line shall be included from top of the vertical gravity line to prevent vacuum, flashing or pulsations.
The vent line should be designed for an air/vapour volumetric flow-rate equal to the liquid volumetric flow
through the vertical line and a pressure loss of maximum 0,005 bar. The vent line for vertical lines/caissons
to sea, shall also be designed for the wave motion inside lines/caisson.
The liquid inlet to the “dump caissons” should be tangential and sloped downwards.
Drainage of deluge water from drain boxes through vertical lines shall be sized on basis of 50 % of the
available head (assuming the pipe running full of liquid) and not Froude number. The following formulas can
be used to determine the capacity:
8855,8 × D 2,5
Q= (2)
f
where
Q is the flow in m3/h
f is the Moody friction factor
D is the pipe inner diameter in m
NORSOK standard Page 11 of 22
h a n g e Vi h a n g e Vi
XC e XC e
F- w F- w
PD
PD
er
er
!
!
W
W
O
O
N
N
y
NORSOK standard P-001 Edition 5, Sep. 2006
y
bu
bu
to
to
k
k
lic
lic
C
C
w
w
m
m
w w
w
w
o
o
.d o .c .d o .c
c u -tr a c k The Moody friction factor for fully turbulent flow can be calculated by the Nikuradse formula, given by: c u -tr a c k
1
f = 2
(3)
⎡ D ⎤
⎢⎣2 log( 2k ) + 1.74⎥⎦
where the pipe diameter D and pipe roughness k shall be given in the same units.
The flow formula is based on setting 50 % of the available head equal to the piping friction loss i.e.
f × L × ρ ×V 2
ρ × g × 0,5 × L = (4)
D×2
where
ρ is the density in kg/m3
L is the pipe length in m
V is the velocity in m/s
g is the gravity constant in m/s2
6.2.6 Fire water
The line sizing of fire water lines shall be based on available system pressure and allowable flow velocities.
The pressure drop to the large deluge systems shall be calculated on basis of the most unfavourable pipe
routing to those systems.
In the ring main pipe-work the flow velocity shall not exceed the velocity as given in Table 2. Upstream the
deluge skids, the flow velocities should not exceed 10 m/s. Some areas may require velocities higher than
10 m/s in order to hydraulically balance the systems, which is acceptable provided the reaction force within
the system does not cause excessive stress in the pipe work or the supports.
6.2.7 Oily water systems
Where retaining the size of oil droplets in the water is crucial, this can be achieved by providing low flow
velocities. Typically the velocity should not exceed 3 m/s. This should also be considered in selection of
fittings and instruments in these lines to avoid shearing of oil droplets.
6.3 Sizing of gas lines
6.3.1 General
When sizing gas lines the sizing criteria will be a compromise between the maximum velocity (see 6.3.2) and
allowable pressure drop, see 6.3.3.
Piping with gas at the dew-point and/or with some droplets shall be designed as gas lines.
6.3.2 Maximum velocities
In lines where pressure drop is not critical, gas velocity shall not exceed limits which may create noise or
vibrations problems. As a rule of thumb the velocity should be kept below:
0 , 43
⎛1⎞
V = 175 × ⎜⎜ ⎟⎟ (4)
⎝ρ⎠
where
V is the maximum velocity of gas to avoid noise in m/s
3
ρ is the density of gas in kg/m
or 60 m/s, whichever is lowest.
NORSOK standard Page 12 of 22
