Page 153 - Petroleum Production Engineering, A Computer-Assisted Approach

Guo, Boyun / Computer Assited Petroleum Production Engg 0750682701_chap11 Final Proof page 148 3.1.2007 8:54pm Compositor Name: SJoearun

11/148 EQUIPMENT DESIGN AND SELECTION
e ¼ 2.718 and where
q ¼ volumetric flow rate, Mcfd
0:0375g g Dz
s ¼ , (11:107) p pc ¼ pseudocritical pressure, psia
T T z z d ¼ pipe internal diameter, in.
and Dz is equal to outlet elevation minus inlet elevation L ¼ pipe length, ft
(note that Dz is positive when outlet is higher than inlet). p r ¼ pseudo-reduced pressure
A general and more rigorous form of the Weymouth equa- T ¯ ¼ average flowing temperature, 8R
tion with compensation for elevation is g g ¼ gas gravity, air ¼ 1.0
s ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi z b ¼ gas deviation factor at T b and p b , normally
s 2
2
p e p )d 5
3:23T b accepted as 1.0.
q h ¼ ( 1 2 , (11:108)

TzzL
p b f M g g T e
Based on Eqs. (2.29), (2.30), and (2.51), Guo and Ghalam-
where L e is the effective length of the pipeline. For a bor (2005) generated curves of the integral function
p
s
uniform slope, L e is defined as L e ¼ (e 1)L . Ð r p r z dp r for various gas-specific gravity values.
s
For a non-uniform slope (where elevation change cannot 0
be simplified to a single section of constant gradient), an 11.4.1.2.6 Pipeline Efficiency All pipeline flow equ-
approach in steps to any number of sections, n,willyield ations were developed for perfectly clean lines filled with
(e 1) e (e 1) gas. In actual pipelines, water, condensates, sometimes
s 1
s 2
s 1
L e ¼ L 1 þ L 2 crude oil accumulates in low spots in the line. There are
s 1 s 2
often scales and even ‘‘junk’’ left in the line. The net result
n
e s 1 þs 2 (e 1) X is that the flow rates calculated for the 100% efficient cases
s 3
þ L 3 þ .. .. .. :: þ
s 3 are often modified by multiplying them by an efficiency
i¼1 factor E. The efficiency factor expresses the actual flow
P
i 1
s j capacity as a fraction of the theoretical flow rate. An
e j¼1 (e 1) efficiency factor ranging from 0.85 to 0.95 would
s i
L i , (11:109) represent a ‘‘clean’’ line. Table 11.1 presents typical
s i
values of efficiency factors.
where
Table 11.1 Typical Values of Pipeline Efficiency
0:0375g g Dz i
s i ¼ : (11:110) Factors
T T z z
Liquid content
11.4.1.2.3 Panhandle-A Equation for Horizontal Type of line (gal/MMcf) Efficiency E
Flow The Panhandle-A pipeline flow equation assumes
the following Reynolds number–dependent friction factor: Dry-gas field 0.1 0.92
Casing-head gas 7.2 0.77
0:085
f M ¼ (11:111) Gas and condensate 800 0.6
N 0:147
Re
The resultant pipeline flow equation is, thus,
1:07881 0:5394 11.4.2 Design of Pipelines
2
2
d 2:6182 T b ( p p )
q ¼ 435:87 1 2 , (11:112) Pipeline design includes determination of material, diam-
g 0:4604 p b T T zzL eter, wall thickness, insulation, and corrosion protection
g
measure. For offshore pipelines, it also includes weight
where q is the gas flow rate in scfd measured at T b and p b , coating and trenching for stability control. Bai (2001)
and other terms are the same as in the Weymouth equa- provides a detailed description on the analysis–analysis-
tion.
based approach to designing offshore pipelines. Guo et al.
(2005) presents a simplified approach to the pipeline
11.4.1.2.4 Panhandle-B Equation for Horizontal Flow design.
(Modified Panhandle) The Panhandle-B equation is The diameter of pipeline should be determined based on
the most widely used equation for long transmission and flow capacity calculations presented in the previous sec-
delivery lines. It assumes that f M varies as tion. This section focuses on the calculations to design wall
0:015 thickness and insulation.
f M ¼ , (11:113)
0:0392
N Re
11.4.2.1 Wall Thickness Design
and it takes the following resultant form: Wall thickness design for steel pipelines is governed by
1:02 " 2 2 # 0:510 U.S. Code ASME/ANSI B32.8. Other codes such as
2
1
q ¼ 737d 2:530 T b ( p p ) (11:114) Z187 (Canada), DnV (Norway), and IP6 (UK) have es-
p b T T zzLg 0:961 sentially the same requirements but should be checked by
g
the readers.
11.4.1.2.5 Clinedinst Equation for Horizontal Flow Except for large-diameter pipes (>30 in.), material
The Clinedinst equation rigorously considers the deviation grade is usually taken as X-60 or X-65 (414 or 448 MPa)
of natural gas from ideal gas through integration. It takes for high-pressure pipelines or on deepwater. Higher grades
the following form: can be selected in special cases. Lower grades such as X-42,
X-52, or X-56 can be selected in shallow water or for low-
z b p b p pc
q ¼ 3973:0 pressure, large-diameter pipelines to reduce material cost
p b or in cases in which high ductility is required for improved
v ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
0
1
u p p impact resistance. Pipe types include
u d 5 ð r1 ð r2
u
t @ p r dp r p r dp r A , (11:115)
z z . Seamless
T Tf M Lg g
0 0
. Submerged arc welded (SAW or DSAW)