2. Pipeline Design-Hydrotest

SUBSEA PIPELINE DESIGN CRITERIAHYDROTEST CONDITION

CHAPTER IPREFACE

This file provides detail calculation for designing subsea pipeline that includes:

Wall thickness selection;•On-bottom stability analysis; and•Free-span analysis•

Detail calculation here only provides for hydrotest condition, while calculation on other condition has been provided in other file.

CHAPTER IIDESIGN BASIS

2.1 Pipeline Design Parameter.

Corrosion coating thickness tcorr 4mm:=

Outer diameter Ds 24in 609.6 mm⋅=:=

2.2 Material Properties

Steel density ρs 490pcf 7.849 103

× kg m3−

⋅⋅=:=

Corrosion coating density ρcorr 80pcf:=

Concrete coat density ρcc 190pcf 3.044 103

× kg m3−

⋅⋅=:=

Modulus elasticity E 207000MPa 3.002 107

× psi⋅=:=

Coefficient of thermal expansion α 11.7 106−

⋅ K1−

:=

Structural damping δ 0.126:=

Poisson ratio ν 0.3:=

Pipeline material API5L_Gr_X 52:=

SMYS 290MPa API5L_Gr_X 42=if

317MPa API5L_Gr_X 46=if






:= SMYS 3.59 108

× Pa=

SMTS 414MPa API5L_Gr_X 42=if







:= SMTS 4.55 108

× Pa=

Manufacturing process Seamless = 1

UO; TRB; ERW = 2

UOE = 0.85

PF 1:=

2.4 Environmental Parameter

Pipeline condition Installation = 1

Hydrotest = 2

Operation = 3

PC 2:=

Highest astronomical tide HAT 0.53m:=

Lowest astronomical tide LAT 0.61m:=

Water depth dmax 22.708m HAT+:= dmax 23.238m=

dmin 14.935m HAT+:= dmin 15.465m=

Kinematic viscosity of seawater v 1.076 105−

⋅ ft2sec

1−⋅:=

Seawater density ρsw 64pcf 1.025 103

× kg m3−

⋅⋅=:=

Gravity( ) g 9.807 m s2−

⋅⋅=

Current at 90% water depth Ur 0.45m s1−

⋅ PC 1= PC 2=∨if

0.48m s1−

⋅ PC 3=if

:= Ur 0.45m

s=

Significant wave height Hs 1.8m PC 1= PC 2=∨if

3.6m PC 3=if

:= Hs 1.8m=

Significant Wave period Ts 6.3s PC 1= PC 2=∨if

8.3s PC 3=if

:= Ts 6.3 s=

2.5 Pipeline Operational Data

Content density ρcont 0kg m3−

⋅ PC 1=if

1025kg m3−

⋅ PC 2=if

57.522pcf PC 3=if

:=

Design pressure Po 0psi PC 1=if

1350psi PC 3=if

1.5 1350⋅ psi PC 2=if

:=

Design temperature Td 140F:=

Seabed temperature Tsw 23 °C:=

Corrosion allowance Ca 2.54mm:=

External pressure Pe.max ρsw g⋅ dmax⋅:= Pe.max 2.336 105

× Pa=

Pe.min ρsw g⋅ dmin⋅:= Pe.min 1.555 105

× Pa=

Axial pressure Fa 0N:=

Bending stress M 72% SMYS⋅:= M 258.48 MPa⋅=

2.6 Soil Parameter

Soil type 1 = sand

2 = clay

soil 2:=

Medium density of sand ρsand 1860kg m3−

⋅:=

Medium density of clay ρclay 326.309kg m3−

⋅:=

Medium density of soil ρsoil ρsand soil 1=if

ρclay soil 2=if

:= ρsoil 326.309kg

m3

=

Undrained shear stress Su 2kPa:=

2.8 Design Factor

Internal pressure factor design

ASME B31.4 F1 0.72:=

API RP 1111 fd 0.72:=

Weld joint factor

ASME B31.8 Ee 1:=

API RP 1111 fe 1:=

Temperature derating factor

ASME B31.8 T 1:=

API RP 1111 ft 1:=

Collapse factor

ASME B31.8

f0 0.7:=API RP 1111

Ovalitas

DNV OS F101 fo 0.005:=

Propagation buckling design factor

ASME B31.8

fp 0.8:=API RP 1111

Local buckling factor

DNV 1981

ηxp 0.72:=Longitudinal stress usage factor

Hoop stress usage factor ηyp 0.92:=

Material resistance factor γm 1.15:=

Incidental factor γinc 1.05:=

CHAPTER IIIWALL THICKNESS SELECTION

3.1 Internal Pressure Collapse Criteria

3.1.1 Internal Pressure Contaiment ASME B31.8 Design Criteria

Initial wall thickness tint.ipc.ASME 17mm:=

Hoop stress σy

Po Pe.max−( )2 tint.ipc.ASME⋅

Ds⋅:= σy 2.461 108

× Pa=

Internal pressure contaiment criteria IPC_ASME_Criteria "accepted" σy F1 SMYS⋅≤if

"not accepted" otherwise

:=

IPC_ASME_Criteria "accepted"=

Safety factor SFipc.ASME

F1 SMYS⋅

σy

:= SFipc.ASME 1.05=

3.1.2 Internal Pressure Contaiment API RP 1111 Design Criteria

Initial steel wall thickness tint.ipc.API 16mm:=

Minimum pressure burst Pb.API 0.9 SMYS SMTS+( )⋅tint.ipc.API

Ds tint.ipc.API−⋅:=

Internal pressure contaiment criteria IPC_API_Criteria "accepted" Po fd fe⋅ ft⋅ Pb.API⋅≤if

"not accepted" otherwise

:=

IPC_API_Criteria "accepted"=

Safety factor SFipc.API

fd fe⋅ ft⋅ Pb.API⋅

Po

:= SFipc.API 1.018=

3.2 External Pressure Collapse

External pressure (Pe) on hydrotest condition is smaller than internal pressure (Pi), hence wall thickness selection

calculation on external pressure collapse criteria isn't done in this condition.

3.3 Local Buckling Criteria


calculation on local buckling criteria isn't done in this condition.

3.4 Propagation Buckling Criteria


calculation on API RP 1111 propagation buckling criteria isn't done in this condition.

3.5 Selected Wall Thickness

This following t.int.ins is selected wall thickness from hydrotest condition.

The final selected wall thickness is obtain from comparing this initial wall thickness eith other initial wall thicness

from installation and operation condition.

tint.hyd max tint.ipc.ASME tint.ipc.API, ( ):=

tint.ins 9mm:=(Obtained from installation condition calculation)

tint.hyd 17 mm⋅=

tint.op 18.54mm:= (Obtained from operation condition calculation)

tcalc max tint.ins tint.hyd, tint.op, ( ):= tcalc 0.73 in⋅=Selected wall thickness from calculation

Selected wall thickness Pipe OD 6.625" WT 0.75" ts 0.75in:=

CHAPTER IVON BOTTOM STABILITY ANALYSIS

4.1 Vertical Stability

4.1.1 Pipe Weight Calculation

Initial concrete coating thickness tint.cc 0mm:=

Internal diameter ID Ds 2 ts Ca−( )⋅− := ID 576.58 mm⋅=

Corrosion coating diameter Dcorr Ds 2 tcorr⋅+:= Dcorr 617.6 mm⋅=

Total outer diameter Dtot Ds 2 tcorr⋅+ 2 tint.cc⋅+:= Dtot 617.6 mm⋅=

Steel pipe mass / length mst

π

4Ds2

ID2

−

⋅ ρs⋅:= mst 241.454

kg

m=

Corrosion coating mass / length mcorr

π

4Dcorr

2Ds2

−

⋅ ρcorr⋅:= mcorr 9.881

kg

m=

Concrete coat mass / length mcc

π

4Dtot

2Dcorr

2−

⋅ ρcc⋅:= mcc 0

kg

m=

Content mass / length mcont

π

4ID2

⋅ ρcont⋅:= mcont 267.629kg

m=

Added mass;

Dicplaced water; Buoyancy / length

Bπ

4Dtot

2ρsw⋅:= B 307.118

kg

m=

Total pipe mass / length mtot mst mcorr+ mcc+ mcont+ B−:=

mtot 211.846kg

m=

Total pipe weight / length Wtot mtot g⋅:= Wtot 2.077 103

×N

m⋅=

4.1.2 Vertical Stability Calculation

Vertical stability VS

mtot B+( )B

:= VS 1.69=

Vertical_Stability "accepted" VS 1.1>if

"not accepted; enlarge concrete coating thickness" VS 1.1≤if

:=

Vertical_Stability "accepted"=

4.2 Lateral Stability

4.2.1 Hydrodynamics Parameter Calculation

4.2.1.1 Wave-Induced Particle Velocity

Spectral peak period Tp 1.05 Ts⋅:= Tp 6.615 s=

Periode

referensi

Tn

dmin

g:= Tn 1.256 s=

Peakedness

parameterϕ

Tp

Hs

:= ϕ 4.931s

m0.5

=

γ 5 ϕ 3.6sec

m

≤if

1 ϕ 5sec

m

≥if

3.3 otherwise

:= γ 3.3=

Figure 4.1 Significant water velocity, Us* (DNV RP E305)

Water particle velocity

(Wave induced)

Tn

Tp

0.19=

Us

0.22 Hs⋅

Tn

:= Us 0.315m

s=

4.2.1.2 Zero-Up Crossing Period

Figure 4.2 Zero-up crossing period, Tu (DNV RP E305)

Zero-up crossing period Tu 1 Tp⋅:= Tu 6.615 s=

4.2.1.3 Average Velocity on Pipeline

Velocity on 90% depth Ur 0.45m

s=

The amount of current passing through the pipe is affected by the type of seabed soil in which the pipe is laid.

In terms of the soil is clay soil, the soil roughness is negligible, so in this case UD = Ur

UD Ur:= UD 0.45m

s=

4.2.1.4 Hydrodynamics coefficient

Reynold's number Re

UD Us+( )v

Dtot⋅:= Re 4.728 105

×=

Wave - current velocity ratio M

UD

Us

:= M 1.427=

Drag coefficient CD 1.2 Re 5 104

⋅<if

1.3 5 104

⋅ Re< 1 105

⋅<if

1.53Re

3105

⋅

− 1 105

⋅ Re< 2.5 105

⋅<if

0.7 otherwise

:= CD 0.7=

Lift coefficient CL 1.5 Re 5 104

⋅<if

1 5 104

⋅ Re< 1 105

⋅<if

1.2Re

5105

⋅

− 1 105

⋅ Re< 2.5 105

⋅<if

0.7 otherwise

:= CL 0.7=

Inertia coefficient CM 2 Re 2.5 105

⋅<if

2.5Re

5105

⋅

− 2.5 105

⋅ Re< 4.9 105

⋅<if

1.5 otherwise

:= CM 9.457− 109

×=

4.2.2 Seabed Soil Factor

Figure 4.4 Recommended friction factors for clay (DNV RP E305)

ratio

Dtot Su⋅

mtot g⋅:= ratio 0.595=

Soil friction

factor

μ 2.3:=

4.2.3 Hydrodynamics Force

Wave particle acceleration As 2 π⋅Us

Tu

⋅:= As 0.3m

s2

=

fL. θ( )1

2

ρsw

g⋅ Dtot⋅ CL⋅ Us cos θ( )⋅ UD+( )2⋅:=

Lift force

Drag force fD. θ( )1

2

ρsw

g⋅ Dtot⋅ CD⋅ Us cos θ( )⋅ UD+( )2⋅:=

Inertia force fI. θ( ) πDtot

2

4⋅

ρsw

g⋅ CM⋅ As⋅ sin θ( )⋅:=

4.2.4 Lateral Stability Calculation

4.2.4.1 Calibration Factor

Figure 4.3 Calibration factor, Fw, as function of K and M (DNV RP E305)

K

Us Tu⋅

Dtot

:= K 3.378=Keulegan-Carpenter number

Calibration factor Fw 1:=

4.2.4.2 Lateral Stability Check

i 0 180..:=phase angle range

θi i deg⋅:=

Required submerged weight ms. θ( )fD. θ( ) fI. θ( )+( ) μ fL. θ( )⋅+

μ

Fw⋅:=

mreq. θ( ) max ms. θ( )( ):=

mreq. θ( ) 18.991kg

m=

SFw

mtot

mreq. θ( ):= SFw 11.155=

LS "accepted" SFw 1≥if

"not accepted, enlarge concrete coating thickness" SFw 1<if

:=LATERAL STABILITY

LS "accepted"=

CHAPTER VFREE-SPAN ANALYSIS

5.1 Static Analysis

Static span length Lfr.st 50m:=

Total pipe weight / length Wtot 2.077 103

×N

m⋅=

Drag force FD max fD. θ( )( ) g⋅:= FD 129.803N

m⋅=

Inertia force FI max fI. θ( )( ) g⋅:= FI 0N

m⋅=

Support type 1 = pinned - pinned

2 = fixed - pinned

3 = fixed - fixed

support 1:=

End condition constant( ) Cfr.st 8 support 1=if

10 support 2=if

12 support 3=if

:= Cfr.st 8=

Distributed pipe weight Wd Wtot2

FD2

FI2

+

2

+:= Wd 2.082 103

×N

m⋅=

Area moment of inertia Iπ

64Ds4

ID4

−

:= I 1.354 10

3−× m

4⋅=

Section modulus ZI

Ds

2

:= Z 4.441 103−

× m3

⋅=

Longitudinal stress σl

Wd Lfr.st2

⋅

Cfr.st Z⋅:= σl 1.465 10

8× Pa=

Hoop stress σy 2.461 108

× Pa=

Equivalent stress σe σl2

σy2

+:= σe 2.864 108

× Pa=

Allowable stress σallow 0.72 SMYS⋅( ) PC 1=if

0.9 SMYS⋅( ) PC 2= PC 3=∨if

:=

σallow 3.231 108

× Pa=

Static span criteria static_span_criteria "Static span length accepted" σe σallow<if

"Minimize static span length" otherwise

:=

static_span_criteria "Static span length accepted"=

Safety factor SFfr.st

σallow

σe

:= SFfr.st 1.128=

5.2 Dynamic Analysis

5.2.1 Critical Span Length

5.2.1.1 Stability Parameter

Effective mass meff mst mcorr+ mcc+ mcont+ B+:=

meff 826.082kg

m=

Stability parameter Ks

2 meff⋅ δ⋅

ρsw Dtot2

⋅:= Ks 0.532=

5.2.1.2 Reduced Velocity

Figure 5.1 Reduced velocity for cross-flow oscillations based on the reynolds number.

Figure 5.2 Reduced velocity for inline oscillations based on the stability parameter

Reynold's number Re 4.728 105

×=

Reduced velocity for cross-flow

oscillation

Vr.cf 5.9:=

Reduced velocity for inline oscillation Vr.in 1.4:=

5.2.1.3 Critical Span Length

End condition constant Cfr.dy π2

support 1=if

15.5 support 2=if

22 support 3=if

:= Cfr.dy 9.87=

Critical span length for cross-flow

motion

Lfr.dy.cf

Cfr.dy Vr.cf⋅ Dtot⋅

2 π⋅ Us Ur+( )E I⋅

meff

⋅:= Lfr.dy.cf 65.997m=

Critical span length for inline motion Lfr.dy.in

Cfr.dy Vr.in⋅ Dtot⋅

2 π⋅ Us Ur+( )E I⋅

meff

⋅:= Lfr.dy.in 32.149m=

Critical span selected for dynamic

analysis criteria

Lfr.dy min Lfr.dy.cf Lfr.dy.in, ( ):= Lfr.dy 32.149m=

5.2.2 Dynamic Stress

5.2.2.1 Vortex Shedding Frequency

Figure 5.3 Strouhal's number for circular cylinder as function of Reynold's number

Reynold's number Re 4.728 105

×=

Strouhal's number St 0.2:=

Vortex shedding frequency fv

St Us Ur+( )⋅

Dtot

:= fv 0.2481

s=

5.2.2.2 Pipeline Natural Frequency

Pipeline natural frequency fn

Cfr.dy

2 π⋅

E I⋅

meff Lfr.dy4

⋅

0.5

⋅:= fn 0.8851

s=

Pipe frequency criteria pipe_frequency_check "pipeline critical span accepted" fv 0.7fn≤if

"redesign pipe" otherwise

:=

pipe_frequency_check "pipeline critical span accepted"=

DEFINITION

pcflb

ft3

:=

year 31536000sec:=C K:=

2. Pipeline Design-Hydrotest

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