PEMILIHAN MATERIAL DAN DESAIN TEBAL PIPA KL4220 PIPA BAWAH LAUT
PROF. Ir. Ricky Lukman Tawekal, MSE, PhD Eko Charnius Ilman, ST, MT
topics WALL THICKNESS STUDY & MATERIAL GRADE SELECTION
Material selection Corrosion Protection System Hydraulic & Flow Assurance Introduction to Stress & Strain on Pipeline Wall thickness Determination Buckling [Local & General]
Material selection
Material selection A. Material & Grade Selection Generally, pipe material is based on the following criteria: 1.Operating
& design condition 2.Type of pipe content 3.Installation method, 4.Material availability 5.Codes requirement 6.Weight requirement 7.Economics, cost 8.Resistance to corrosion effects 9.Weldability The type of material grade of pipeline can be selected based on API 5L, DnV OS-F101 (2000)
Material selection B. Pipeline Material Component Selection Standard fittings: • Flanges • Valves • Bends • Tees • Bolts&Nuts • Tie-In • Reducer
Valves
Gate valve
Ball Valve
Globe Valve
Tie in
Flange
Swivel Flange Missalignment Missalignment flange flange
Smart Flange
Pipeline Components 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)
Normal flow
Normal flow
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. 11.
Grades A25 A B X42 X46 X52 X56 X60 X65 X70 X80
STEEL MATERIAL Baja untuk struktur dengan tempa panas dapat diklasifikasikan sebagai: Baja karbon (carbon steel), Baja paduan rendah berkekuatan tinggi (high strength low alloy steel), dan Baja paduan (alloy steel). Persyaratan umum untuk jenis-jenis baja sedemikian ini tercakup dalam spesifikasi ANSI / ASTM A6.
STEEL MATERIAL Baja karbon (carbon steel), Baja karbon struktural termasuk. dalam kategori karbon lunak. Suatu baja, misalnya A36, memiliki karbon maksimum antara 0.25- sampai 0.29% tergantung dari ketebalannya. Peningkatan persentase karbon akan meningkatkan kekerasannya namun akan mengurangi kekenyalannya, hingga lebih sulit dilas. Baja karbon dibagi menjadi empat kategori berdasarkan presentase karbonnya: – Karbon rendah (kurang dari 0.15%); – Karbon lunak (0.15-0.29%); – Karbon sedang (0.30-0.59%); dan – Karbon tinggi (0.60-1.70%).
Baja paduan rendah berkekuatan tinggi (high strength low alloy steel), Kategori ini meliputi baja-baja yang memiliki tegangan leleh dari 40 sampai dengan 70 ksi (275 sampai dengan 480 MPa). Penambahan sejumlah elemen paduan terhadap baja karbon seperti krom, kolumbium, tembaga, mangan, molibden, nikel, fosfor, vanadium, atau zirkonim, akan memperbaiki sifat-sifat mekanisnya. Bila baja karbon mendapatkan kekuatan dengan penambahan kandungan karbonnya, elemenelemen paduan menciptakan tambahan kekuatan lebih dengan mikrostruktur yang halus ketimbang mikrostruktur yang kasar yang diperoleh selama proses pendinginan baja. Baja paduan rendah berkekuatan tinggi digunakan dalam kondisi seperti tempaan atau kondisi normal; yakni kondisi di mana tidak digunakan perlakuan panas.
STEEL MATERIAL
Baja paduan (alloy steel). Baja paduan rendah dapat didinginkan dan disepuh supaya dapat mencapai kekuatan leleh sebesar 80 sampai dengan 110 ksi (550 sampai dengan 760 MPa). Kekuatan leleh biasanya didefinisikan sebagai tegangan pada regangan offset 0.2%, karena baja ini tidak menunjukkan titik leleh yang jelas. Baja paduan rendah ini pada umumnya memiliki kandungan karbon sekitar 0.20% supaya dapat membatasi kekerasan mikrostruktur butilan kasar (martensit) yang mungkin terbentuk selama perlakuan panas atau pengelasan, sehingga dapat mengurangi bahaya retakan.
Material grade selection
Material grade selection
Material grade selection
Material grade selection
Pengenalan Penentuan Diameter Pipa
Pipe Sizing
Penentuan diameter pipa biasanya dilakukan oleh tim proses, dengan simulasi. Biasanya dengan software pipesim, olga, hysis. Banyak pertimbangannya, salah 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, wax, and asphaltene may be 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 deposition. Based on the hydrate/wax/asphaltene 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 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.
Desain tebal Pipa
Pertanyaan..
Mengapa perlu mendesain tebal pipa?
Topics for Wall Thickness Study
Introduction – Design Codes & Standard – Mechanical Perspective Internal Pressure Containment External Pressure Collapse Local Buckling Buckle Propagation
Material & grade select. Wall thickness study
CODES & STANDARD TO BE USED 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 Gas, Anhydrous Ammonia and Alcohol. (ASD) 4. ASME B.31-8, Gas Transmission and Distribution Piping Systems. (ASD) 5. BS8010, Codes of Practices for Pipeline, 1993 (ASD) 6. DnV 1981, Rules for Submarine Pipeline Systems, 1981 (ASD) 7. DnV 2000 (OS F-101), Rules for Submarine Pipeline Systems, October 2007 (LRFD) 8. ASTM (American Society for Testing & Materials) Referances: 1. A.H. Mouselli, Introduction to Submarine Pipeline Design Installation, and Construction, 1976 2. Andrew 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)
Sebelum masuk ke pembahasan mengenai desain tebal pipa, Dalam slide berikut ini akan dikenalkan mengenai - Konsep Tegangan dan regangan pada pipa - Coating pada pipa
Stress – strain analysis Concept of Stress & Strain Stress Strain
: Stress of a material is the internal resistance per unit area to the deformation caused by applied load : Strain is unit deformation under applied load.
Normal Stress
y : tekanan tangensial (hoop stress)
y
L
y
Pi
Pe
R
L
P E
= = = =
P/A /L /Young’s modulus-modulus elastisitas) P.L/A.E
Pe L
y R
Pi
L
Stress – strain analysis
Hoop stress around circumference, y , (i.e pressure containment) Longitudinal stress, L ,along pipe axis
y : tekanan tangensial (hoop stress) y
Pi
Pe
L
R
L Pe L
y R
Pi
L
HOOP STRESS
Perhatikan silinder bebas dengan jari-jari a , ketebalan dinding t , dan panjang L
HOOP STRESS
Perhatikan silinder bebas dengan jari-jari a , ketebalan dinding t , dan panjang L Struktur silinder tersebut dikenai beban tekanan P, P = Po – Pi Po, tekanan luar; Pi, tekanan dalam Dari free-body pada gambar tersebut, keseimbangan gaya dalam arah vertikal adalah:
Tekanan tangensial (hoop stress)
HOOP STRESS
LONGITUDINAL/AXIAL STRESS
Silinder juga mengalami tegangan aksial yang disebabkan oleh beban tekanan pada kedua ujungnya dimana gaya aksial yang terjadi adalah:
Luas penampang melintang silinder adalah 2at . Maka, tegangan aksial yang terjadi adalah:
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 due to Pressure
Poisson’s Effect: Hoop stress creates circumferential (lateral) strain Poisson’s ratio = lateral strain/longitudinal strain = 0.3 for steel Fully restrained pipeline cannot move - tensile 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 h (for thin walled pipe)
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 due to temperature partially restrained - equilibrium between expansion and friction restraint (section of pipe which expands) fully restrained when friction resistance = fully restrained force i.e. no movement
Temperature stress is as follows : L = - E (T2 - T1)
-
e.g. 6-inch x 14.3mm wt 60 degrees above ambient results in a stress of 145 MPa full restraint force = 1017 kN or 100 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 due to Bending
Spanning (resting on an irregular seabed) Lay radius curvature Bending within elastic range, formulae as follows : M==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
Combined Stress
Von Mises (maximum distortion energy theory) Allowable design factor for combined equivalent pipeline stress is high, can be 0.96 Von Mises equivalent Stress, e , is given by:
Von Mises Failure Envelope
Stress – strain analysis Concept of Stress & Strain
Shear Stress
P
L
G
= P/A = tan = /L = /
xy
Stress – strain analysis Stress – Strain Curve
Stress – strain analysis Stress – Strain Curve
Stress – strain analysis SMYS = Specified Minimum Yield Strength/Stress SMTS = Specified Minimum Tensile Strength
Above SMYS value there is a plastic region SMTS itu tegangan pada saat material mulai mengalami “pengecilan luas penampang” necking pada saat ditarik (titik M) Antara SMYS dan SMTS material tidak mengalami pengecilan luas penampang Akan terjadi necking sebelum material putus Setelah SMTS material mulai mengecil luas penampangnya, tegangan masih tetap diberikan namun menurun dari SMTS lalu akhirnya putus (titik F) Failure point (F) Perbandingan antara SMTS/SMYS disebut strength ratio (Y/T) nah sebenernya material yang paling ideal untuk struktur dan komponen permesinan adalah yang strength rationya paling besar. The 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 reduction of area. The first two are strength parameters; the last two indicate ductility.
Stress – strain analysis Untuk material yg sangat getas/rapuh (brittle) misal keramik...yg mungkin tdk mengalami necking sama sekali... SMTS sama dengan tegangan pd saat putus... Untuk steel, pada umumnya merupakan material yg tangguh/dapat dibentuk (ductile)... akan terjadi necking sebelum material putus...dimana .titik tertinggi stress terjadi sesaat sebelum necking....itulah SMTS nya
Berikut ini merupakan paparan mengenai Coating pada pipa
Cross section of pipe
Line pipe Corrosion coating – FBE – Adhesive – Polypropelene
Concrete coating
Anti corrosion coating type capability
fabrication Blast Cleaned Pipe (3LPE)
Internal Coating
3LPE Inspection
Pipe Storage
Pipe properties
Coating Cutback
Field joint coating section, Anti corrosion coating layer (HSS) & Infill (PUF)
Bahasan Selanjutnya..
Desain Tebal Pipa
PIPELINE PROPERTIES (sample) No. 1
2
3
3.
Data
Nilai
Pipe Properties Outside Diameter
81.28
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 Coating Properties 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 Joint Properties
WALL THICKNESS
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
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 either platform or facility
0.5
Allowable Stress Criteria
A: Weight; B: Pressure; C: Temperature; D: Environment; E: Hoop Stress; F: Von Mises Equivalent Stress; Note 1- Allowable stresses are : 0.72 at Sagbend and 0.96 at Stinger Overbend
Mechanical design Additional Considerations
Negative mill tolerance (API 5L or DnV OSF 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 i.e. for fatigue implications
Langkah desain tebal pipa Input Calc 1 Calc 2 Calc 3 Calc 4 Pilih
• Data Pipa, Properti material, data operasi dan lingkungan pipa. • Internal Pressure Containment • Collapse due to External Pressure • Propagation Buckling • Local Buckling • Tebal Pipa sesuai API 5L
Perhitungan 1 Internal Pressure Containment
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 (barlow formulae):
y Pi Pe Do t
= = = = =
hoop stress (tensile) internal pressure external pressure outside diameter nominal pipe wall thickness
1. Internal Pressure Containment
ASME B31.8
Where, D = Outside Diameter of Pipe E = Longitudinal Joint Factor F = Design Factor P = Design Pressure (Pi), 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%) t selected > t req (Lihat Tabel Standard Pipa)
ASME B31.4
1. Internal Pressure Containment
API RP 1111
The following equations must be satisfied:
The specified minimum burst pressure (Pb) is determined by one of the following formulae:
(1)
a)
(2)
b)
c)
Where D Di S t U
= = = = =
outside diameter of pipe 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
Where,
fd = Internal Pressure Design Factor fe = Weld Joint Factor Factor ft = Internal Pressure Design Factor Pa = Incidental Overpressure Pb = Specified Minimum Burst Pressure Pd = Pipeline Design Pressure Pt = Hydrostatic Test Pressure
1. Internal Pressure Containment
DNV 1981
1. Internal Pressure Containment
DnV OS-F101 The pressure containment shall fulfill the following criteria:
Where
Where,
pb,s(t) pb,u(t) pli SC m
= = = = =
Yielding Limit State Bursting Limit Limit State Local Incidental Pressure Safety Class Resistance Factor Material Resistance Factor
Perhitungan 2 External Pressure Collapse
2. External Pressure Collapse
API RP 1111 The following criteria must be satisfied: Where,
Where fo = Collapse Factor Pc = Collapse Pressure of Pipe Pe = Elastic Collapse Pressure of Pipe P0 = External Hydrostatic Pressure
Py = Yield Pressure at Collapse v = Poisson’s Ratio (0.3 for steel)
2. External Pressure Collapse
DnV OS-F101
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The following criteria must be met:
Where
2. External Pressure Collapse
DnV OS-F101
Where,
pc = Characteristic Collapse Pressure pe1 = Elastic Collapse Pressure pp = Plastic Collapse Pressure fo = Ovality αfab = Fabrication Factor
LOCAL BUCKLING
Buckling and Collapse 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 pressure - no internal 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
Layability
The allowable stress for pipeline subjected to both functional and environmental loads during 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:
85% of SMYS
Allowable Sagbend Stress :
72% of SMYS
Buckling and Collapse Three buckling scenarios to consider : collapse - water depth where collapse can occur with negligible longitudinal stress initiation - water depth where a buckle may be initiated due to a combination of effects propagation - water 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-F101, 2007: Collapse Pressure - the pressure required to buckle a pipeline. Initiation pressure - the pressure required to start a propagating buckle from a given buckle. This pressure will depend on the size of the initial buckle Propagating 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: Pc>Pinit>Ppr
Buckling and Collapse
Buckle during laying
Collapse pipe
Buckle during laying
Propagating Buckling
3. Local Buckling
BUCKLING CHECK Local Buckling : Based on DnV 1981
Dimana : = Longitudinal Stress (MPa) = Hoop Stress (MPa)
xcr = Critical Longitudinal Stress (MPa) ycr = Critical Hoop Stress (MPa) nxp = Permissible Usage Factor for Longitudinal Stress nyp = Permissible Usage Factor for Hoop Stress α
=
DnV 1981 (combination between internal pressure and longitudinal pressure)
3. Local Buckling
DNV 1981
a)
b)
c)
The following criteria must be satisfied:
3. Local Buckling
DNV 1981
d)
e)
f)
3. Local Buckling
DNV 1981
g)
h)
i)
j)
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)
BUCKLE PROPAGATION
Propagation Buckling • Propagating pressure based on DnV 1981
Ppr > Pe ----- it is OK
INITIATION & PROPAGATION BUCKLING • Initiation & Propagation Buckle based on API RP 1111 Buckle cannot be initiated or propagated within a portion of pipe where the maximum external overpressure is less than the propagation of the pipe: Initiation buckling (Battele formula):
Propagation buckling: Pp = Buckle Propagation Pressure fp = Propagating Buckle Design Factor Po = External Hydrostatic Pressure
DnV OS F101
The following equations have to be satisfied: a)
b)
Comparison Table OD = 914.4 mm; P = 15 MPa; WD = 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
Conservative one is DnV 81 & Least conservative is DnV OS-F101
SUMMARY AND CONCLUSIONS 1.
Material Selection is based on the following: – – – – – – – – –
2.
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
SEKIAN…..
TERIMA KASIH
