VALIDATION REPORT FOR 2-PHASE LINE SIZING

PART 1

A. INTRODUCTION This is a report to validate the 2-phase line sizing spreadsheet used on the MPNU Slot

Addition Project. It explains the steps, criteria and standards applied in sizing the 2-phase line.

B. CRITERIA FOR SIZING A 2-PHASE LINE (API RP 14E PAGE 23)

The 2-phase fluid velocity should not exceed the erosional velocity The minimum velocity should not be less than 10 ft/s to minimize slugging of

separation equipment.

C. PROCESS DATA Operating conditions of the 2-phase line will be derived from the Heat and Material Balance

prepared from HYSYS simulation. This will also be used for the purpose of validating the calculation procedure described in this report.

D. 2-PHASE LINE SIZING:

1. Erosional velocity The erosional velocity is determined using equation 2.14 (API RP 14E, Page 23)

1................................ DCVm

e =

Where: =eV Erosional velocity, ft/sec. C = Empirical constant m = Gas / liquid mixture density at flowing pressure and temperature, Ib/ft3

2. Mean Density The density of the gas / liquid mixture is calculated using equation 2.15 (API RP 14E Page 23).

m 2...........................7.1987.212409

DRTZP

PSPS gl++=

Where: =m Mean density, Ib/ft3 P = Operating pressure, psia lS = Liquid specific gravity (water = 1; use average gravity for

Hydrocarbon-water mixtures) at standard conditions. R = Gas / liquid ratio, ft3/bbl T = Operating temperature, R =gS Gas specific gravity at standard conditions

Z = Gas compressibility factor, dimensionless 3. Minimum Cross-sectional Area

This is the area required to avoid fluid erosion. It is determined from equation 2.16 (API RP 14E, Page 23.)

3............................................25.2135.9

DV

PZRT

Ae

+=

Where: A = Minimum pipe cross-sectional flow area required, in2/1000bbl liquid per day.

4. Pressure Drop

Using equation 2.17 (API RP 14E, Page 24), the pressure drop is determined thus;

4.............................................000336.0 52

Dd

fWPmi

=

Where: P = Pressure drop, psi/100ft =id Pipe inside diameter, in f = Moody friction factor, dimensionless =m Mean density, Ib/ft3 =W Total liquid plus vapor rate, Ibs/hr

NOTE: The use of this equation D.4 should be limited to 10% pressure drop due to inaccuracies associated with changes in density.

5. Mean Liquid Specific Gravity Per API RP 14E, Page 47,

Slm 5.........................................21 DQQSQSQ

Wl

lWll

++=

Where: Slm = Mean liquid specific gravity lQ = Oil flow rate, bbl/day =1lS Specific gravity of oil =WQ Produced water flow rate, daybbl / =2lS Specific gravity of water / oil mixture

6. GOR The GOR is the ratio of gas flow rate to the oil flow rate (API RP 14E, Page 47)

6.............................................. DQQ

GORl

g=

Where: =gQ Gas flow rate, ft3 /day =lQ Liquid flow rate, bbl/day

7. Fluid Velocity

Per API RP 14E, Page 48, fluid velocity is determined using the formula:

V = 7..............................................

)12(4 2D

dVt

i

where: V= Fluid velocity, ft/sec. Vt = Total volume flow, ft3/sec. di = Inside diameter, in.

8. 2V Calculation

is the mean density, Ib/ft3 V is the fluid velocity,ft/s.

9. Minimum Required Line Size

9......................................4 DAd =

where: A = Minimum pipe cross- sectional area,in2

PART 2

A. VALIDATION OF EXCEL SPREADSHEET This manual calculation is performed to validate the 2-phase line sizing excel spreadsheet shown in attachment 1. The calculation is based on the solved example in API RP 14E (example A1), in which a gas condensate flow line was sized (see attachment 2). This calculation is to validate the selection of a 3 line for the final flow conditions.

.

B. GENERAL DATA Line pressure, P 1500 psig (1514.7 psia)

Temperature, T 120F (580 R)

C. GAS PROCESS DATA Gas flow rate, Qg 10mmscfd Specific gravity 0.65 Dynamic viscosity 0.81

D. LIQUID PROCESS DATA Oil flow rate, Ql 200 bbl/day Specific gravity 0.80 Dynamic viscosity 1.28 cP Water flow rate 1500 bbl/day Water specific gravity 1.08

E. PIPE DATA Nominal diameter 3 in Piping class D Size / Schedule 3-XXS Roughness 0.0019 Empirical constant, C 100 Internal diameter 2.3 in

F. CALCULATION 1. Mean Liquid specific gravity. From equation D.5,

)(meanLS = 21 LWLL SQSQ + WL QQ +

)(meanLS = 1500200)08.11500()80.0200(

++

)(meanLS 17001620160 +=

17001780=

)(meanLS 0471.1= 2. GOR From equation D.6, GOR = mmscfd10 dbbldbbl /1500/200 + GOR = 5882.3529 ft3/bbl 3. Mean Density From equation D.4,

RTZP

PSPS glm +

+=7.198

7.212409

m )81.0)(580)(3529.5882()7.1514)(7.198()7.1514)(65.0)(3529.5882)(7.2()7.1514)(0407.1)(12409(

++=

m 392.276352989.30097089.1563704918.19679320

++=

m = 11.5243 Ib/ft3

4. Total Mass flow W = LLgg SQSQ 6.143180 + W = (3180)(10)(0.65)+14.6(1500+200)(1.0471) 20670+25986.54 W = 46,659.022 Ib/hr 5. Pressure Drop From equation D.4, 2000336.0 fWP = mdi 5 P = 2)54.656,46(002.0000336.0 )5243.11(5)3.2( P = 14628.31591 741.743 P = 19.7 psi/100ft

6. Erosional Velocity From equation D.1,

m

eCV =

eV = 100

5243.11 = 29.4573 ft/s 7. Fluid Velocity From equation D.7, V = tV

2)12/(4/ id = 1.12 2)12/3.2()4/142.3( V = 38.813 ft/s 8. 2V 22 )813.38(5243.11 =V

2V = 77.360,17 Ib/ft/s2

9. Minimum Pipe Cross-sectional Area A= PZRT 25.21/35.9 + (from equation D.3) eV

A = 9.35+ (0.81)(5882.3529)(580)/(21.25)(1514.7) 29.4573 A = 3.2321 in2/1000 bbl/day

A = 3.23 in2/1000 bbl/day (1500 bbl/day + 200 bbl/day) = 5.494 in. 10. Minimum Required Line Size From equation D.9, d = /4A d = 142.3/49.54 d = 2.64 in Friction factor The friction factor used for the purpose of this validation report was taken from API RP 14E sample calculation. There is no basis for establishing the friction factor used in the sample calculation since the viscosity of the fluid is not stated in the example thus making it impossible to establish the Reynolds number to be used on Moody friction factor graph.

For all other cases, the Moody friction factor shall be determined from the iterative solution developed by Colebrook or Olga friction factor correlation which also gives the same answer as Colebrook. (See GPSA-chapter 17 page 4.)

Colebrook: ( ) )51.27.3

(log21Re10

mm fDf+=

Olga: [ ]3/1)1000000)20000((10055.0eRd

f ++=

CONCLUSION The 2-phase line sizing excel spreadsheet and the manual calculation gave the same results as shown in API RP 14E Appendix A sample calculation.

REFERENCES API Recommended practice 14E Offshore Production Platform Piping

System GPSA Engineering Data Book.

ATTACHMENTS Attachment 1: Excel spreadsheet for 2-phase line sizing Attachment 2: API RP 14E, Appendix A. Attachment 3: GPSA Section 17.

Revision: 0Date: 18-Sep-08

Cakasa Nig. Company Ltd. Issued By: O.IClient: Mobil Producing Nigeria Unlimited Checked By: O.OProject: Ubit GA & GC Slot Addition Project Approved By: O.O

Description Unit

Line Number -Hysys Stream Number - API 14E Initial API 14E Final API 14E FinalLine pressure psig 4500 1500 4500Temp oF 120 120 120

Flow Rate mmscfd 15 10 10Specific Gravity - 0.65 0.65 0.65Compressibility - 0.91 0.81 0.81

Oil Flowrate bbl/day 750 200 200Specific Gravity - 0.80 0.80 0.80

Water Flowrate bbl/day 0 1500 1500Water Specific Gravity - 1 1.08 1.08

Nominal Diameter inch 4 3 4

Piping class. - D D D

Size / Schedule - 4- XXS 3- XXS 4- XXS

Roughness inch 0.0019 0.0019 0.0019Empirical Constant; C - 100 100 100

Absolute Pressure psia 4514.70 1514.70 1514.70

Absolute Temperature oR 580 580 580Total Stream Mass Flow Lb/hr 39,765 46,658.00 46,658.00Total Stream Volume Flow ft3/s 0.62 1.125 1.127

Friction factor - 0.0196 0.02 0.0196

Internal Diameter (ID) inch 3.152 2.3 3.152

Mean Liquid SG - 0.80 1.0471 1.0471GOR ft3/bbl 20,000 5,882.35 5,882.35Mean density lb/ft3 17.75 11.5 11.5

Pressure drop psi/100ft 1.9 19.7 4.0

Erosional Velocity ft/s 23.7 29.5 29.5Fluid Velocity ft/s 11.48 38.97 20.796v2 Lb/ft/s 2,340.47 17,504 4,973.2Minimum Pipe Cross Sectional Area in2 3.77 5.49 5.49Minimum Required Line Size in 2.19 2.64 2.64Selected Line Size in 4.00 3.00 4.00

Comments :

Intermediate

Results

Gas Process Data

Liquid Process Data

Pipe Data

2-PHASE LINE SIZING - API 14EInput

General Data

CAKASACAKASA

Pressure Loss Due to FrictionFlow is always accompanied by friction. This friction results

in a loss of energy available for work. A general equation forpressure drop due to friction is the Darcy-Weisbach2 (often re-ferred to as simply the Darcy) equation. This equation can berationally derived by dimensional analysis, with the excep-tion of the friction factor, fm, which must be determined ex-perimentally. Expressed in feet of fluid this equation is:

hL = fm L V2

2 g DEq 17-6

Converting to pounds per square inch, the equation be-comes:

Pf = fm L V2

(144) D (2gc) Eq 17-7It should be noted that the Moody friction factor3, fm, is used in

the equations above. Some equations are shown in terms of theFanning friction factor, ff, which is one fourth of fm (fm = 4.0 ff). Agraph of both Fanning and Moody friction factors as a functionof Reynolds number appears in Fig. 17-2.

The Darcy-Weisbach equation is valid for both laminar andturbulent flow of any liquid, and may also be used for gases withcertain restrictions. When using this equation, changes in eleva-tion, velocity, or density must be accounted for by applying Ber-noullis theorem. The Darcy-Weisbach equation must be appliedto line segments sufficiently short such that fluid density is es-sentially constant over that segment. The overall pressure drop

is the sum of the Pf values calculated for the individual seg-ments. For gas applications the segmental length may be rela-tively short, as compared to liquid applications, since many gasapplications involve compressible gases where gas densities varywith pressure.

Friction Factor and Effect of Pipe RoughnessWhen the fluid flow is laminar (Re

/D, which is the roughness of the pipe, , over the pipe diame-ter, D. Fig. 17-2 incorporates the relative roughness of the pipeinto the determination of the friction factor. Fig. 17-3 indicatesrelative roughness and friction factors for various piping ma-terials. These figures are based on the iterative solution of thefollowing equation developed by Colebrook.4

1fm = 2 log10

3.7 D+ 2.51

Re fm

Eq 17-11

Equivalent Length of Valves and FittingsThe pressure drop effects of valves and fittings can be ac-

counted for by addition of the "equivalent lengths" of the fit-tings to the actual piping lengths. This augmented pipe lengthis then used in any of the following pressure drop calculationtechniques. A table of equivalent lengths for a number of rep-resentative valves and fittings appears in Fig. 17-4.

Compressibility of GasesFor more accurate values of Z, refer to Section 23. For more

approximate calculations, the value of the average compressi-bility factor, Zavg, may be calculated from the following equa-tions:

Zavg = 1(Fpv)2 Eq 17-12and

Fpv = 1 +(Pavg) (3.444 ) (105) (10(1.785) (S))

Tavg3.825

Eq 17-13

Fig. 17-5 contains a plot of the deviation factor, Fpv, virtuallyidentical to those calculated by this equation.

An estimate for Zavg at pressures below 100 psi is:

Zavg = 11 + 0.0002 Pavg Eq 17-14

SINGLE PHASE FLOW

Transmission Line Gas FlowIsothermal Flow The steady-state, isothermal flow be-

havior of gas in pipelines is defined by a general energy equa-tion of the form:

Q = 38.77 TbPb

E1

ff

P1

2 P22S Lm Tavg Zavg

0.5

d2.5 Eq 17-15

This equation is completely general for steady-state flow,and adequately accounts for variations in compressibility fac-tor, kinetic energy, pressure, and temperature for any typicalline section. However, the equation as derived involves an un-specified value of the transmission factor, 1/ff . The correctrepresentation of this friction factor is necessary to the valid-ity of the equation.

The friction factor is fundamentally related to the energylost due to friction. In the derivation of the general energyequation, all irreversibilities and non-idealities, except forthose covered by the real gas law, have been collected into thefriction loss term.

Empirical methods historically and currently used to calcu-late or predict the flow of gas in a pipeline are the result ofvarious correlations of the transmission factor substitutedinto the general energy equation.

Examination of the relationships presented by variousauthors shows that their forms differ primarily in the inherentor specified representation of the transmission factor whichdefines the energy lost in resistance to flow for various pipesizes, roughnesses, flow conditions, and gases.

To obtain Eq 17-15, which is convenient for general calcula-tions, a number of simplifying assumptions have been made.For other than pipeline sections with a very high pressuregradient, the change in the kinetic energy of the gas is notsignificant, and is assumed equal to zero. It is also assumedthat the gas temperature is constant at an average value forthe section considered; the compressibility factor is constantat the value characterized by the average gas temperature andpressure; and in the term giving the effect of elevation change,the pressure is constant at the average value. In the range ofconditions to which pipeline flow equations are ordinarily ap-plied, averages are usually sufficiently accurate. Average tem-peratures are calculated as indicated in Fig. 17-1.

The average pressure in the line can be computed by:

Pavg = 23 P1 + P2 P1 P2P1 + P2

Eq 17-16

In the absence of field data indicating otherwise, an effi-ciency factor, E, of 1.0 is usually assumed.

The AGA Equations The AGA Equations were devel-oped to approximate partially and fully turbulent flow usingtwo different transmission factors. The fully turbulent flowequation accounts for the relative pipe roughness, /D, basedon the rough-pipe law.4 This equation uses the following trans-mission factor:

1/ff = 4 log10 3.7 D

Eq 17-17

When the transmission factor for fully turbulent flow is sub-stituted in the general energy equation (Eq 17-15), the AGAEquation for fully turbulent flow becomes:

Q = 38.77 TbPb

E

4 log103.7 D

P12 P22

S Lm Tavg Zavg

0.5

d2.5

Eq 17-18The partially turbulent flow equation is based on the

smooth-pipe law4 and is modified to account for drag-inducingelements. The transmission factor for this equation is:

1/ff = 4 log10 Re1/ff 0.6 Eq 17-19Substituting 1/ff from Eq 17-19 into Eq 17-15 does not pro-

vide an equation which can be solved directly. For partiallyturbulent flow a frictional drag factor must also be applied toaccount for the effects of pipe bends and irregularities. Thesecalculations are beyond the scope of this book and the AGA"Steady Flow in Gas Pipelines"6 should be consulted for a de-tailed treatment of partially turbulent flow.

The Weymouth Equation The Weymouth Equation,published in 19127, evaluated the coefficient of friction as afunction of the diameter.

ff = 0.008d1/3

Eq 17-20

1/ff = 11.18 d1/6 Eq 17-21When the friction factor, ff, is substituted in the general en-

ergy equation, Weymouths Equation becomes:

17-4