KL 4220
PIPA BAWAH LAUT KULIAH #3 MATERIAL GRADE AND WALL THICKNESS SELECTION
Prof. Prof. Ricky Lukman Tawekal
MATERIAL GRADE SELECTION
Material Selection Generally, Generally, pipe material is based on the following following criteria: • • • • • • • • •
Operating & design condition Type of pipe content Installation Installation method Material availability Codes requirement Weight requirement Economics, cost Resistance to corrosion effects weldability
The type of material grade of pipeline can be selected based on API 5L and DNV OS-F101
Pipeline Component Component Pipeline Material Component Component Selection Standard fittings: • Flanges • Valves Valves • Bends • Tees • Bolts&Nuts • Tie-In • Reducer
Pipeline Component Component Valves
Gate valve
Ball Valve
Globe Valve
Pipeline Component Component Tie in
Flange
Swivel Flange Missalignm Missalignment ent flange flange
Missalignm Missalignment ent flange flange
Pipeline Component Component Typical Flange Facings
Pipeline Component Component Flanges: • Subsea use high integrity ring type joints (RTJ) • Pipelines usually use standard ASME/ANSI B16.5 or API • For subsea use swivel ring and possibly misalignment flanges
Tees: Standard Tee Inspection pigging of run only possible if branch size is less than 60% of run (No Inspection pigging from branch) Barred Tee Inspection pigging of run possible for all branch sizes (No Inspection pigging from branch) N o r m a l f l o w
N o r m a l f l o w
Normal flow
Normal flow
Normal flow
Material Grade Selection As API 5-L: The grades covered by this spec are: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Grades A25 A B X42 X46 X52 X56 X60 X65 X70 X80
Steel Material Baja untuk stru strukt ktur ur deng dengan an temp tempa a panas panas dapa dapatt dikl diklas asifi ifika kasi sika kan n seba sebaga gai: i:
Baja Baja karbo karbon n (carbon steel ), ),
Baja Baja padua paduan n rend rendah ah berk berkek ekua uata tan n tingg tinggii (high strength low alloy steel ), ), dan
Baja Baja pad paduan uan (alloy steel ). ).
Persy ersyar arat atan an umum umum untu untuk k jeni jeniss-je jeni niss baja baja sede sedemi miki kian an ini ini terc tercak akup up dala dalam m spes spesif ifik ikas asii ANSI ANSI / ASTM ASTM A6.
Steel Material Baja karbon (carbon steel ) Baja Baja karb karbon on strukt struktur ural al terma termasuk suk.. dalam dalam kate kategor gorii karbo karbon n lunak. lunak. Suatu Suatu baja, baja, misa misaln lnya ya A36, A36, memi memili liki ki karb karbon on maks maksim imum um anta antarra 0.25 0.25-- sampai sampai 0.29 0.29% % terg tergan antu tung ng dari dari keteba ketebalann lannya. ya. Peningk Peningkata atan n persent persentase ase karbon karbon akan meningka meningkatkan tkan keke kekeras rasanny annya a namu namun n akan akan mengu mengurrangi angi keken ekenya yala lann nnya ya,, hingg hingga a lebi lebih h suli sulitt dila dilas. s. Baja Baja karb karbon on diba dibagi gi menj menjad adii empa empatt kate katego gori ri berd berdasa asark rkan an pres presen enta tase se karb karbon onny nya: a: Karb rbon on rend rendah ah (kur (kuran ang g dari dari 0.15 0.15%) %);; – Ka Karbon lunak lunak (0.15(0.15-0.2 0.29%) 9%);; – Karbon Karbon sedang sedang (0.30(0.30-0.5 0.59%) 9%);; dan – Karbon Karbon tinggi tinggi (0.60(0.60-1.7 1.70% 0%). ). – Karbon
Steel Material Baja padu paduan an ren enda dah h be berk rkek ekua uata tan n ting tinggi gi (high strength low alloy steel )
Katego Kate gori ri ini ini meli melipu puti ti baja baja-b -baj aja a yang yang memi memili liki ki tega tegang ngan an lele leleh h dari dari 40 samp sampai ai deng dengan an 70 ksi ksi (275 (275 sam sampa paii deng dengan an 480 480 MPa) MPa)..
Penam enamba baha han n seju sejuml mlah ah elem elemen en padu paduan an terha erhada dap p baja baja karbo arbon n sepe sepert rtii krom krom,, kolumbium, kolumbium, tembaga, mangan, molibden, nikel, fosfor, fosfor, vanadium, atau zirkonim, zirkonim, akan akan mempe memperba rbaiki iki sifatsifat-sif sifat at meka mekanis nisny nya. a.
Bila Bila baja baja karb karbon on mend mendap apat atka kan n kekua ekuata tan n deng dengan an pena penamb mbah ahan an kandun andunga gan n karbo karbonn nnya ya,, eleme elemenel nelem emen en paduan paduan mencip menciptak takan an ta tamba mbahan han kekuat ekuatan an lebih lebih denga dengan n mikr mikros ostru truktu kturr yang yang halus halus ketimb etimbang ang mikro mikrostr strukt uktur ur yang yang kasar kasar yang yang dipero diperoleh leh selama selama prose prosess pendin pendingin ginan an baja. baja.
Baja Baja padua paduan n rend rendah ah berk berkek ekua uata tan n tingg tinggii digu diguna naka kan n dala dalam m kondi ondisi si sepe sepert rtii temp tempaan aan atau at au kondi ondisi si norm normal al;; yakni yakni kondi ondisi si di mana mana tida tidak k digu diguna naka kan n perl perlak akua uan n panas panas..
Steel Material Baja paduan (alloy steel ). ).
Baja Baja padu paduan an renda endah h dapa dapatt didi diding ngin ink kan dan dan dise disepu puh h supa supay ya dapa dapatt menc mencap apai ai kekua ekuata tan n lele leleh h sebe sebesa sarr 80 samp sampai ai deng dengan an 110 110 ksi ksi (550 (550 sam sampa paii deng dengan an 760 760 MP MPa) a)..
Keku Kekuat atan an lele leleh h bias biasan any ya dide didefi fini nisi sika kan n seba sebaga gaii tega tegang ngan an pada pada rega regang ngan an offset 0.2%, karen arena a baja baja ini ini tida tidak k menu menunj njuk ukk kan titi titik k lele leleh h yang ang jel jelas as
Baja Baja padu paduan an renda endah h ini ini pada pada umum umumn nya memi memili liki ki kandu andung ngan an karbo arbon n seki sekita tarr 0.20 0.20% % supay supaya a dapat dapat memba membatas tasii keker ekerasa asan n mikr mikros ostru truktu kturr butila butilan n kasar kasar (mart (martens ensit) it) yang yang mung mungki kin n terb terben entu tuk k sela selama ma perl perlak akua uan n pana panass at atau au peng pengel elas asan an,, sehin sehingg gga a dapa dapatt mengu mengura rangi ngi bahay bahaya a retak retakan. an.
Steel Material
Steel Material
Steel Material
Steel Material
Steel Material
PIPE DIAMETER SELECTION
Pipe Sizing •
•
•
•
Penen Penentua tuan n diame diamete terr pipa biasan biasanya ya dilak dilakuk ukan an oleh oleh tim prose proses, s, dengan dengan simula simulasi. si. Bias Biasan anya ya dengan software software pipesim, pipesim, olga, hysis. Banyak Banyak pertimban pertimbangan ganny nya, a, salah satunya satunya flow assurance Flow assurance is required to determine the optimum flowline pipe size based on reservoir well fluid test results for the required flowrate and pressure. As the pipe size increases, the arrival pressure and temperature decrease. Then, the fluid may not reach the destination and hydrate, hydrate, wax, and asphaltene may be formed formed in the flowline. If the pipe size is too small, the arrival pressure and temperature may be too high and resultantly a thick wall pipe may be required and a large thermal expansion is expected. It is important to determine the optimum pipe size to avoid erosional velocity and hydrate/ wax/asphaltene wax/asphaltene deposition. Based on the hydrat hydrate/wax/ e/wax/asphaltene asphaltene appearance appearance temperature, the required OHTC is determined to choose a desired insulation system (type, material, and thickness.) If the flowline is to transport a sour fluid containing H2S, CO2, etc., the line should be chemically treated or a special corrosion resistant alloy (CRA) pipe material should be used.
Pipe Sizing The blue solid line represents represents inlet pressure at wellhead and the red dotted line represents outlet fluid temperature. The 8” ID pipe may require a heavy (thick) wall and the 12” ID pipe may require a thick insulation coating depending on hydrate (wax or asphaltene) formation temperature.
Pipe Sizing The blue solid line represents represents inlet pressure at wellhead and the red dotted line represents outlet fluid temperature. The 8” ID pipe may require a heavy (thick) wall and the 12” ID pipe may require a thick insulation coating depending on hydrate (wax or asphaltene) formation temperature.
WALL THICKNESS CALCULATION
Wall Thickness Calculation Topics for Wall Wall Thickness Thickness Study Study •
Introduction Design Codes & Standard Mechanical Perspective
•
Internal Pressure Containment
•
External Pressure Collapse
•
Local Buckling
•
Buckle Propagation
Codes & Standards Standards The following codes & standard will be used: 1. API 5L, Specification for Line Pipe, 2000 2. API RP 1111, “Design, Construction, Operation and Maintenance of Offshore Hydrocarbons Pipelines”. (LRFD) 3. ASME B.31-4, Liquid Transportation System for Hydrocarbon, Liquid Petroleum Petroleum Gas, Anhydrous Anhydrous Ammonia and Alcohol. (ASD) 4. ASME B.31-8, Gas Transmission and Distribution Piping Systems. Systems. (ASD) 5. BS8010, Codes of Practices for Pipeline, 1993 (ASD) 6. DnV 1981, Rules for Submarine Pipeline System Systems, s, 1981 (ASD) 7. DnV 2000 (OS F-101), Rules for Submarine Submarine Pipeline System Systems, s, October 2007 (LRFD) 8. ASTM (American Society for Testing & Materials) References: 1. A.H. Mouselli, Introduction to Submarine Pipeline Design Installation, and Construction, 1976 2. Andrew Palmer Palmer,, Roger A King, Subsea Pipeline Engineering, Penwell 2004 3. Yong Bai, Pipeline and Riser, 2000
Mechanical Design Subsea Pipeline:
Design for code compliance
Design to resist internal pressure (pressure containment – hoop stress)
Design for other stresses (longitudinal, bending & combined)
Design to resist external pressure (collapse)
Pipeline components (fittings, flanges, tees etc)
Hoop Stress Perhat Perh atik ikan an sili silind nder er be beba bass de deng ngan an ja jari ri-j -jar arii a , kete keteba bala lan n dind dindin ing g t , dan dan pa panj njan ang g L
sy : tekanan tangensial (hoop stress)
sy
Pi
Pe
sL
sR
sL
Pe sL
sy sR
Pi
L
Hoop Stress Perhat Perh atik ikan an sili silind nder er be beba bass de deng ngan an jari jari-j -jar arii a , keteba ketebalan lan dindin dinding g t , dan dan pa panj njan ang g L
F
P A
L P ( (a t ) sin d )( dz) 0 0
2 F
sin
y
y
r
a
(a) sin d 0
L dz 0
L
2 F
P(a t ) sin d dz 0 0
L
2F P(a t ) sin d dz 0 0 0
Hoop Stress Perhat Perh atik ikan an sili silind nder er be beba bass de deng ngan an jari jari-j -jar arii a , keteba ketebalan lan dindin dinding g t , dan dan pa panj njan ang g L Stru Strukt ktur ur sili silind nder er ters terseb ebut ut dike dikena naii be beba ban n teka tekana nan n P, P = Po – Po – Pi Po, Po, tekana tekanan n luar; luar; Pi, Pi, tekana tekanan n dalam dalam Dari free-body pa pada da ga gamb mbar ar ters terseb ebut ut,, kese keseim imba bang ngan an ga gaya ya da dala lam m arah arah vert vertik ikal al ad adal alah ah:: L
2 F P(a t ) sin d dz 0 0 0
t
L
2F P a sin d dz 0
a
1
0 0
L
2 F P a cos dz 0 0
0
Tekanan tangensial (hoop stress)
L
2 F P a (1 1)dz 0 0
2F
2P L
F
P L
A
s
Lt F A
PaL Lt
Pa t
PD
2t
Hoop Stress Perhat Perh atik ikan an sili silind nder er be beba bass de deng ngan an jari jari-j -jar arii a , keteba ketebalan lan dindin dinding g t , dan dan pa panj njan ang g L Stru Strukt ktur ur sili silind nder er ters terseb ebut ut dike dikena naii be beba ban n teka tekana nan n P, P = Po – Po – Pi Po, Po, tekana tekanan n luar; luar; Pi, Pi, tekana tekanan n dalam dalam Dari free-body pa pada da ga gamb mbar ar ters terseb ebut ut,, kese keseim imba bang ngan an ga gaya ya da dala lam m arah arah vert vertik ikal al ad adal alah ah:: L
2 F P(a t ) sin d dz 0 0 0
t
L
2F P a sin d dz 0
a
1
0 0
L
2 F P a cos dz 0 0
0
Tekanan tangensial (hoop stress)
L
2 F P a (1 1)dz 0 0
2F
2P L
F
P L
A
s
Lt F A
PaL Lt
Pa t
PD
2t
Longitudinal Stress Sili Silind nder er ju juga ga meng mengal alam amii tega tegang ngan an aksi aksial al yang yang dise diseba babk bkan an oleh oleh be beba ban n teka tekana nan n pad pa da ked kedua uj ujun ung gnya nya dim diman ana a ga gaya ya aksi aksial al yan yang ter terja jadi di ad adal alah ah:: F
P A
Fa
P
a
2
Luas Luas pena penamp mpang ang me melilint ntan ang g sili silind nder er ad adala alah h 2 a Maka, tegang tegangan an aksial aksial yang terjad terjadii at t . Maka, adalah: s z
F z A
P a
2
2 at
Pa
2t
PD
4t
Longitudinal Stress Longitudinal Stress: Pressure (two effects dependent on pipeline restraint) – Fully restrained pipeline gives “Poisson’s Effect” – Unrestrained pipeline gives “End Cap Effect” Temperature/Thermal Stress Bending Stress (Span, lay radius curvature, residual lay tension)
Longitudinal Stress Longitudinal Stress due to Pressure Poisson’s Effect: -
Hoop stress creates circumferential (lateral) strain Poisson’s ratio = lateral strain/longitudinal strain/longitudinal strain = 0.3 for steel Fully restrained restrained pipeline cannot cannot move - tensile stress stress developed Longitudinal stress (due to Poisson’s effect) = 0.3 x Hoop Stress
End Cap Effect: pressure differential acting over internal CSA pipe end (hence “End Cap”) unrestrained pipeline at ends (near expansion spool) force (due to End Cap) = /4. (Di2.Pi-Do2.Po) Long’l Stress (end-cap)
= /4. (Di2.Pi-Do2.Po) / CSA = 0.5 sh (for thin walled pipe)
Longitudinal Stress Longitudinal Stress due to Temperature
-
Stress dependent upon axial pipeline restraint stress developed when expansion or contraction (i.e. strain) is prevented 3 cases: unrestrained, partially restrained, fully restrained unrestrained - no stress stress due to temperature temperature partially restrained restrained - equilibrium between between expansion and friction restraint (section (section of pipe which expands) fully restrained when friction resistance = fully restrained force i.e. no movement
Temperature stress is as follows : sL = - E (T2 - T1)
e.g. 6-inch 6-inch x 14.3mm wt 60 degrees above ambient ambient results results in a stress stress of 145 145 MPa full restrain restraintt force = 1017 kN or 100 tonnes tonnes to prevent expansion this restraining force would be required always avoid restraining pipe if possible typical anchor length = 1 to 5 km and expansion 0.5 to 1.5m
-
Longitudinal Stress Longitudinal Stress due to Bending
Spanning (resting on an irregular seabed) Lay radius curvature Bending within elastic range, formulae as follows : M=s=E I y R Bending is both tensile and compressive about neutral axis - important to remember when calculating combined stress. i.e. 2 possible values of longitudinal stress
Shear Stress P d
L
t g
G
= P/A = tan = d /L = t / g
txy
Combined Stress Von Mises (maximum distortion distortion energy theory) Allowable design factor for combined equivalent equivalent pipeline stress is high, can be 0.96 0.96 Von Mises equivalent Stress, se , is given by:
s e s
2
y
s
2
L
Von Mises Failure Envelope
(s s ) 3t 2 y
L
) L A N I D U T I G N O L ( l
σ
s s -60 0 e r t S l a p i c n i r P
600
0 0
6 00
-600
Principal Stress -
σh
(HOOP)
Stress – Strain Analysis SMYS = Specified Minimum Yield Strength/Stress Strength/Stress SMTS = Specified Minimum Tensile Strength
Tegang egangan an yang yang berada berada di at atas as nilai nilai SMYS SMYS merupa merupakan kan jangk jangkauan auan kapas kapasit itas as plas plasti tiss dari dari mate materi rial al SMTS SMTS adala adalah h tega tegang ngan an pada pada saat saat mate materi rial al mulai mulai meng mengal alam amii “pengec pengecila ilan n luas luas penampang ” necking pada pada saa saat dit ditarik arik (tit (titiik M) Antar Antara a SMYS SMYS dan SMTS SMTS mate materia riall tidak tidak menga mengalam lamii pengec pengecila ilan n luas luas penampang Akan terjadi terjadi necking necking sebelu sebelum m material material putus Setela Setelah h SMTS SMTS mate materia riall mulai mulai menge mengecil cil luas luas penamp penampang angny nya, a, teg tegang angan an masih masih teta tetap p dibe diberi rik kan namu namun n menu menuru run n dari dari SMTS SMTS lalu lalu akhi akhirn rny ya putu putuss (tit (titik ik F) Failure Failure point (F) Perbandingan antara SMTS/SMYS disebut strength ratio (Y/T). Material yang paling ideal untuk struktur dan komponen permesinan permesinan adalah yang strength rationya paling besar.
The parameters, parameters, which are used to describe the stress-strain curve of a metal, are the tensile strength, yield strength or yield point, percent elongation, and a re strength parameters; parameters; the last two indicate reduction of area. The first two are
Stress – Strain Analysis Untuk Untuk materi material al yg sanga sangatt getas/ getas/rrapuh apuh (brit (brittle tle), ), sepert sepertii kerami eramik, k, tidak tidak mungki mungkin n meng mengala alami mi necking necking sama sama sekali sekali SM SMTS TS sama sama de deng ngan an teg teganga angan n pd saat saat putu putuss Pada umumn umumnya ya baja baja merupa merupaka kan n mate materi rial al yg tanggu tangguh/d h/dapa apatt diben dibentuk tuk (ducti (ductile) le),, maka maka akan akan terja terjadi di necki necking ng sebelu sebelum m mate materia riall putu putuss dimana dimana titik titik terti tertinggi nggi stress stress terja terjadi di sesaat sesaat sebelu sebelum m necking titi titik k ters terseb ebut ut meru merupa paka kan n SM SMTS TS dari dari baja baja
Stress
Strain Curve
Stress – Strain Analysis
Pipe’s Coating Line pipe Corrosion coating •
•
•
FBE Adhesive Polypropelene
Concrete coating l i a e r i p a t a M p
u t l i m i S e r o s k o
C o o n nt t e n e t t n ( i is s i i )
Selimut beton
ID Ds Ds+2tcorr
Anti Corrosion Coating
Wall Thickness Calculation The required wall thickness is determined in order to satisfied pressure containment as well as local and global buckling criteria.
Pipeline Section
Allowable Stress
Zone 1 (Pipeline)
0.72
Zone 2 (Riser & Tie-in Spool)
0.5
Note : Zone 2, is the region within 500m from either platform or facility. Zone 1, otherwise
The required wall thickness is determined in order to satisfied pressure containment as well as local and global buckling criteria.
Zone 1 500m
Zone 2 500m
Pipeline Section Zone 1 (Pipeline) Zone 2 (Riser & Tie-in Spool)
Remarks
Allowable Stress
>500m
0.72
the region within 500m from
0.5
Wall Thickness Calculation Allowable Stress Criteria ALLOWABLE STRESS AS A FACTOR SMYS
LOAD COMBINATION LOAD CONDITION
PIPELINE
1
OPERATING (Functional)
2
OPERATING + 100 ENVIRONMENTAL
3
HYDROTEST (Functional)
4
HYDROTEST + 1 ENVIRONMENTAL
5 6 7
A
B
C
X
X
X
X
X
X
X
X
X
X
X
F
E
F
0.72
0.72
0.5
0.5
X
0.72
0.96
0.5
0.67
0.90
1.00
0.90
1.00
0.90
1.00
0.90
1.00
-
0.72 0.96
-
0.72 0.96
-
0.96
-
0.96
YR
X
INSTALLATION + ENVIRONMENTAL
X
ONSHORE PIPELINE
E
YR
INSTALLATION (Functional) – Note 1 1
D
RISER
X
YR X
X X
X
0.6
A: Weight; B: Pressure; Pressure; C: Temperature; Temperature; D: Environment; E: E: Hoop Stress; F: Von Mises Equivalent Stress;
Wall Thickness Calculation Additional Considerations
Negative Negative mill toleran tolerance ce (API 5L 5L or DnV OSF 101) 101) Corrosion allowance (CA) Temperature de-rating factors – generally applicable to higher temperatures than encountered in subsea pipelines Weld joint factors for relatively high cyclic loading load ing i.e. for fatigue implications
Wall Thickness Calculation
Langkah desain tebal pipa Input
Calc 1
Calc 2
Calc 3
Calc 4
Pilih
• Da Data ta Pipa Pipa,, Prope Propert rtii mat mater eria ial, l, data data oper operas asii da dan n liling ngku kung ngan an pi pipa. pa. • Internal Pressure Containment • Collapse due to External Pressure • Propagation Buckling • Local Buckling • Teb ebal al Pi Pipa pa se sesu suai ai AP APII 5L
Wall Thickness Calculation No. 1
2
3
3.
Data
Nilai
Pipe Pr Properties Outside Diameter
81 . 2 8
cm
Wall Thickness
1.59
cm
Yield Stress
483
Mpa
Average Joint Length
12.19
m
Steel Weight Density
78500
N/m^3
Poisson's Ratio
0.3
Pipe Pipe Coat Coatin ing g Pro Prope pert rtie iess Corrosion Coating Thickness
0.25
cm
Corrosion Coating Density
12800
N/m^3
Concrete Coating Thickness
10
cm
Concrete Coating Density
30340
N/m^3
Concrete Coating Cutback
35
cm
Field Joint Filler Density
18853
N/m^3
Water Depth
Var
Field ield Join Jointt Pro Prope pert rtie iess
Contoh Contoh data data pipa, pipa, property material, dan lingk lingkung ungan an
Wall Thickness Calculation 1. Internal Pressure Containment Hoop Stress: Pipeline is design to be strong enough to withstand the maximum tangential (hoop) stress due to internal pressure. This stress cannot exceed the allowable stress. The hoop stress due to internal pressure is given by (bar (barlo low w form formul ulae ae): ):
s y
sy
Pi Pe Do
= = = =
( Pi
Pe )
2t
Do
hoop stress (tensile) internal pressure external pressure outside diameter nominal pipe wall thickness
Wall Thickness Calculation 1. Internal Pressure Containment ASME B31.8
Pe
P
.g.h
t 2 St
FET
( Pi 2
Pe ) D
S F E T
D Where, D = Outside Diameter of Pipe E = Longitudinal Joint Factor F = Design Factor P = Design Design Pressure (Pi), Pe Pe = Ext Pressure S = Specified Min. Yield Strength (SMYS) T = Temperature Derating Factor t = Nominal Wall Thickness CR = Corrosion Rate (mmpy) DL = Design Life (20-25years) MT = Mill Tolerances (12.5%)
Wall Thickness Calculation 1. Internal Pressure Containment ASME B31.4 B31.4
Where, D = Outside Diameter of Pipe E = Longitudinal Joint Factor F = Design Factor P = Design Design Pressure Pressure (Pi), Pe = Ext Pressure Pressure S = Specified Min. Yield Strength (SMYS) T = Temperature Derating Factor t = Nominal Wall Thickness CR = Corrosion Rate (mmpy) DL = Design Life (20-25years) MT = Mill Tolerances (12.5%)
t A
t req
CR .D L
t t A
(1 MT )
Wall Thickness Calculation 1. Internal Pressure Containment The specified minimum burst pressure (Pb) is API RP 1111
determined by one of the following formulae:
The following equations must be satisfied:
a) b) c)
Pt
f d f t f e Pb
Pd 0.80Pt
Pb
0.45( S
U
) ln
Pb
0.90( S
U
)
Pa 0.90Pt
Where, f d = Internal Pressure Design Factor f e = Weld Joint Factor Factor f t = Internal Pressure Design Factor P a = Incidental Overpressure P b = Specified Minimum Burst Pressure P d = Pipeline Design Pressure
Where D = Di = S = t = U =
D Di t
D
(1) (2)
t
outside diameter of pipe D – D – 2t = inside diameter of pipe Specified minimum yield strength of pipe Nominal wall thickness of pipe Specified ultimate tensile strength of pipe For low D/t pipe (D/t < 15), formula (2) is recommended
Wall Thickness Calculation 1. Internal Pressure Containment DnV OSOS-F101 The pressure containment shall fulfill the following criteria: pb t pli pe g SC g m
Where Pb , s (t )
Pb ,u (t )
2
D
2
D
t
t
SMYS .
t
t
2
SMTS
3 2
3
pb t Mi Min ( pb, s t ; pb,u t
p b,s (t) = Yielding Limit State p b,u (t) = Bursti Bursting ng Limit Limit Limit Limit State State p li = Local Incidental Pressure = Safety Class Resistance Factor g SC = Material Resistance Factor G m
Wall Thickness Calculation 2. External Pressure Collapse API RP 1111 1111 The following criteria must be satisfied: Po Pi f o Pc Where,
Where Pc
P y Pe P y Pe 2
2
f o = Collapse Factor P c = Collapse Pressure of Pipe
t P y 2 S D
P e = Elastic Collapse Pressure of Pipe P0 = External Hydrostatic Pressure
t D Pe 2 E 1 v
P y = Yield Pressure at Collapse
3
2
v = Poisson’s Ratio (0.3 for steel)
Wall Thickness Calculation 2. External Pressure Collapse DnV DnV OS-F OS-F10 101 1 The following criteria must be met:
pc pe pc 1
Where
3
t 2 E D pe1 1 v 2
p p 2 S fab fa b f o
t D
Dmax Dmin D
2
p p
2
pc pe1 p p f o
D t
Wall Thickness Calculation 2. External Pressure Collapse DnV DnV OS-F OS-F10 101 1
pe
pc 1.1 g m g SC
Where, p c = Characteristic Collapse Pressure p e1 = Elastic Collapse Pressure p p = Plastic Collapse Pressure f o = Ovality α fab = Fabrication Factor
Wall Thickness Calculation 3. Local Buckling Pipeline buckling and collapse may occur from : • Hydrostatic (external) pressure • Axial compression • Applied bending • Combination of all of the above More likely during installation : • External External pressure pressure - no internal internal pressure pressure • High bending stress in sag bend (near seafloor) • High bending stress in over bend region • Dynamic considerations, complex behaviour prediction
Installation Analysis
As Input to Buckle Analysis
Wall Thickness Calculation 3. Local Buckling
The allowable stress for pipeline subjected to both functional and environmental loads during installation, installation, in accordance with DNV 1981, is 96%. However, for a conservative design margin, the following stress criteria are adopted in line with standard industry practice: Allowable Overbend Stress: Allowable Sagbend Stress :
85% of SMYS 72% of SMYS
Wall Thickness Calculation 3. Local Buckling Three buckling scenarios to consider : collapse - water depth where collapse can occur with negligible longitudinal longitudinal stress buckle may be initiated due to a combination of initiation - water depth where a buckle effects propagation - water depth depth where a previously initiated buckle would propagate to. • Always size wall for collapse, initiation checked during lay analysis • Propagation can be limited by use of buckle arrestors (thicker section of pipe), see A.H. Mouselli Book DnV OS-F10 OS-F101, 1, 2007 2007:: Collapse Pressure Pressure - the pressure pressure require required d to buckle a pipeline pipeline.. Initiation pressure pressure - the pressure required to start a propagating propagating buckle from a given buckle. This pressure will depend on the size of the initial buckle Propagating pressure pressure - the pressure required to continue a propagating buckle. A propagating buckle will stop when the pressure is less than the propagating pressure. The relationship between the different pressures are: P >Pinit>P
Wall Thickness Calculation 3. Local Buckling
Buckle during laying
Buckle during laying
Wall Thickness Calculation 3. Local Buckling Based o n DnV 1981 1981
s s xp
s s y
x
xcr
yp
1
ycr
Dimana : s
= Longit Lon git udi nal Stress (MPa) (MPa)
s
= Hoop Str Str ess (MPa) (MPa)
x
y
xcr
= Critical Longit udinal Stress Stress (MPa (MPa))
ycr
= Crit ical Hoop Stress (MP (MPa) a)
n xp
= Permi Permi ssib le Usage Usage Factor Factor for Longit udinal Stress Stress
n yp
= Permi Permi ssib le Usage Usage Factor Factor for Hoop Hoop Stress Stress
α
=
1
300 300 D t
.
s y s ycr
DnV 1981 (combination (combination between internal internal pressure and longitudinal pressure) pressure)
Wall Thickness Calculation 3. Local Buckling DNV 1981
The following criteria must be satisfied:
a)
b)
s x s x
N
M
c)
s x
s x
N
M
s x
F A A
0.72 S
Wall Thickness Calculation 3. Local Buckling DNV 1981
The following criteria must be satisfied:
d)
s xcr N
e)
s xcr
M
f)
s xcr
s x
N
s x
M
s xcr N
s x
s x
M
s xcr
D S 1 0.001 20 t D S 1.35 0.0045 t
Wall Thickness Calculation 3. Local Buckling DNV 1981
The following criteria must be satisfied: g)
h)
i)
j)
s
1
y
s
x
D / t
s
y
s
ycr
pe pi
ycr
s s
300
D 2t
t E D t
2
s 1 s y
Wall Thickness Calculation 3. Local Buckling DNV 1981 Where, σx = Longitudinal Stress σxN = Longitudinal Stress (Axial) σxM = Longitudinal Stress (Bending) σxcr = Critical Longitudinal Stress σxcrN = Critical Longitudinal Stress (Axial) σxcrM = Critical Longitudinal Stress (Bending) σycr = Critical Hoop Stress (Pressure)
Wall Thickness Calculation 4. Buckle Propagation Propagating Propagating pressure based on DnV 1981
t p pr 1,15 SMY SMYS D t Ppr > Pe OK
k
Pe_max
1.15 SM Y k D
t
nom
1
k
2
Wall Thickness Calculation 4. Buckle Propagation Propagation Buckle based on API RP 1111 • Initiation & Propagation Buckle cannot be initiated or propagated propagated within a portion of pipe where the maximum external overpressure overpressure is less than the propagation of the pipe: Initiation Initiation buckling (Battele (Battele formula): formula): Pbi
t 0.02 E D
2.064
Propagation Propagation buckling:
Po Pi f p P p
t P p 24S D
2.4
P p = Buckle Propagation Pressure f p = Propagating Buckle Design Factor Po = External Hydrostatic Pressure
Wall Thickness Calculation 4. Buckle Propagation DnV OS F101 101
The following equations have to be satisfied:
a)
b)
t p pr p r 35 S fab fa b D pe
p pr p r g mg S C
2.5
Wall Thickness Calculation Comparison Table OD = 914.4 mm; P = 15 MPa; WD = 50 – 50 – 100m; Content density = 200 kg/m3 ; Wave Ht = 3.8 m ASME B31.8
API RP 1111
DNV 1981
DNV OS-F101
Internal Pressure Containment
20.6 mm
20.46 mm
21.93 mm
19.90 mm
External Pressure Collapse
13.80 mm
13.61 mm
-
14.25 mm
-
-
22.0 mm
-
21.68 mm
21.35 mm
23.42 mm
21.15 mm
Local Buckling Buckle Propagation Propagation
The most most conser conservati vative ve DnV 81 Least conservative Dn DnV V OS-F OS-F10 101 1
Summary and Conclusion •
Material Selection is based on the following: – – – – – – – – –
•
Operating and design condition Type of content Installation method Material availability Weight requirement Codes requirement Economics, cost Resistance to corrosion effects Weldability
Things that have to be check in Wall Thickness Design: – – –
Hoop stress criteria Local Buckling check Propagation Check
