Kuliah-04&05 Pemilihan Material Dan Desain Tebal Pipa

PEMILIHAN MATERIAL DAN

DESAIN TEBAL PIPA

PROF. Ir. Ricky Lukman Tawekal, MSE, PhD

Eko Charnius Ilman, ST, MT

KL4220 PIPA BAWAH LAUT

KULIAH #03Semester II 2014/2015

topics

Material selection Corrosion Protection System Hydraulic & Flow Assurance Introduction to Stress & Strain on Pipeline Wall thickness Determination Buckling [Local & General]

WALL THICKNESS STUDY &

MATERIAL GRADE SELECTION

Material selection

Material selection

A. Material & Grade SelectionGenerally, pipe material is based on the following criteria:

1.Operating & design condition2.Type of pipe content3.Installation method,4.Material availability5.Codes requirement6.Weight requirement7.Economics, cost8.Resistance to corrosion effects9.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 valveBall Valve

Globe Valve

Tie in

Flange

Smart FlangeMissalignment

flange

Swivel Flange

Missalignment 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 TeeInspection pigging of run possible for all branch sizes (No Inspection pigging from branch)

Normal flow Normal flow

Norm

al flo

w

Norm

al flo

w

Normal flow

Material grade selection

As API 5-L:The grades covered by this spec are:

1. Grades A252. A3. B4. X425. X466. X527. X568. X609. X6510. X7011. X80

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.

STEEL MATERIAL

Material grade selection

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, 20002. 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, 19762. Andrew Palmer, Roger A King, Subsea Pipeline Engineering, Penwell

20043. 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 desaintebal pipa, Dalam slide berikut ini akan dikenalkan mengenai- Konsep Tegangan dan regangan pada pipa- Coating pada pipa

Stress strain analysis

Concept of Stress & Strain

L

P

s = P/Ae = d/LE = s/e (Youngs modulus-modulus elastisitas)d = P.L/A.E

d

sy

PiPe

sRsL

sy

sR

sL

Pe

Pi

L

Stress : Stress of a material is the internal resistance per unit area to the deformation caused by applied loadStrain : Strain is unit deformation under applied load.

Normal Stress

sy

sy : tekanan tangensial (hoop stress)


PiPe

sRsL

sy

sR

sL

Pe

Pi

L

Hoop stress around circumference, sy , (i.e pressure containment) Longitudinal stress, sL ,along pipe axis

sy

sy : tekanan tangensial (hoop stress)

sL

HOOP STRESS

Perhatikan silinder bebas dengan jari-jari a , ketebalan dinding t , dan panjang L

0 0

2 ( ( ) sin )( )

L

F P a t d dz

0 0

2 ( ) sin 0

L

F P a t d dz

0

( ) sina d

F P A

siny y

r a

0

L

dz

0 0

2 ( ) sin

L

F P a t d dz

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:

0 0

2 ( ) sin 0

L

F P a t d dz

0 0

2 sin 0

L

F P a d dz

0

2 cos 00

L

F P a dz

0

2 ( 1 1) 0

L

F P a dz

2 2F PaL F PaL

A Lt

2

F PaL Pa PD

A Lt t t

s

Tekanan tangensial (hoop stress)

1t

a

HOOP STRESS

LONGITUDINAL/AXIAL STRESS

Silinder juga mengalami tegangan aksial yang disebabkan oleh beban tekanan pada kedua ujungnya dimana gaya aksial yang terjadi adalah:

F P A 2

aF P a

Luas penampang melintang silinder adalah 2at . Maka, tegangan aksial yang terjadi adalah:

2

2 2 4

zz

F P a Pa PD

A at t t

s

Longitudinal Stress

Longitudinal Stress:

- Pressure (two effects dependent on pipeline restraint)

- Fully restrained pipeline gives Poissons Effect

- Unrestrained pipeline gives End Cap Effect

- Temperature/Thermal Stress

- Bending Stress (Span, lay radius curvature, residual lay tension)

Longitudinal Stress due to Pressure

Poissons Effect:- Hoop stress creates circumferential (lateral) strain- Poissons ratio = lateral strain/longitudinal strain = 0.3 for steel- Fully restrained pipeline cannot move - tensile stress developed- Longitudinal stress (due to Poissons 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)

Longl Stress (end-cap) = /4. (Di2.Pi-Do2.Po) / CSA

= 0.5 sh (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 : sL = - 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 = 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

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, se , is given by:

2 2 2( ) 3ey L y L

s s s s s

-600

0

600

-600 0 600

Principal Stress - h (HOOP)

Pri

nc

ipa

l S

tre

ss

-

l (L

ON

GIT

UD

INA

L)

Von Mises Failure Envelope


Concept of Stress & Strain

Shear Stress

= P/Ag = tan = d/LG = / g

L

Pd

xy


Stress Strain Curve

SMYS = Specified Minimum Yield Strength/StressSMTS = 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.


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 mengenaiCoating pada pipa

Cross section of pipe Line pipe

Corrosion coating

FBE

Adhesive

Polypropelene

Concrete coating

Mat

erial

pipa

Selim

ut

koros

i

Selimut

beton

Content(isi)

ID

Ds

Ds+2tcorr

Ds+2tcorr+2tcc = Dtot

Anti corrosion coating type

capability

fabrication

Blast Cleaned Pipe (3LPE) 3LPE Inspection

Internal Coating Pipe Storage

Pipe properties

Coating Cutback

Field joint coating section, Anti

corrosion coating layer (HSS) & Infill

(PUF)

Bahasan Selanjutnya..

Desain Tebal Pipa

No. Data Nilai

1 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

2 Pipe Coating Properties

Corrosion Coating Thickness 0.25 cm

Corrosion Coating Density 12800 N/m^3

Concrete Coating Thickness 10

Concrete Coating Density 30340 N/m^3

3 Field Joint Properties

Concrete Coating Cutback 35 cm

Field Joint Filler Density 18853 N/m^3

3. Water Depth Var

cm

PIPELINE PROPERTIES (sample)

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

Pipeline Section Remarks Allowable Stress

Zone 1 (Pipeline) >500m 0.72

Zone 2 (Riser & Tie-in Spool) the region within 500m from either platform or facility

0.5

ZONE

500m

500m

Zone 1

Zone 2

The required wall thickness is

determined in order to satisfied pressure

containment as well as local and global

buckling criteria.

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

ALLOWABLE STRESS AS A FACTOR SMYS LOAD COMBINATION

PIPELINE RISER LOAD CONDITION

A B C D E F E F

1 OPERATING (Functional) X X X 0.72 0.72 0.5 0.5

2 OPERATING + 100 YR ENVIRONMENTAL X X X X 0.72 0.96 0.5 0.67

3 HYDROTEST (Functional) X X X 0.90 1.00 0.90 1.00

4 HYDROTEST + 1 YR ENVIRONMENTAL X X X 0.90 1.00 0.90 1.00

5 INSTALLATION (Functional) Note 1 X -

0.72 0.96 -

0.72 0.96

6 INSTALLATION + 1 YR ENVIRONMENTAL X X - 0.96 - 0.96

7 ONSHORE PIPELINE X X X 0.6

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 Data Pipa, Properti material, data operasi dan lingkungan pipa.

Calc 1 Internal Pressure Containment

Calc 2 Collapse due to External Pressure

Calc 3 Propagation Buckling

Calc 4 Local Buckling

Pilih Tebal Pipa sesuai API 5L


Perhitungan 1

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):

sy = hoop stress (tensile) Pi = internal pressure Pe = external pressure Do = outside diameter t = nominal pipe wall thickness

o

ei

y Dt

PP

2

)( s

1. Internal Pressure Containment

ASME B31.8

Where,D = Outside Diameter of PipeE = Longitudinal Joint FactorF = Design FactorP = Design Pressure (Pi), Pe = Ext PressureS = Specified Min. Yield Strength (SMYS)T = Temperature Derating Factort = Nominal Wall ThicknessCR = Corrosion Rate (mmpy)DL = Design Life (20-25years)MT = Mill Tolerances (12.5%)t selected > t req (Lihat Tabel Standard Pipa)

FETD

StP

2 ( )

2

i eP P DtS F E T

ASME B31.4

. .eP g h

(1 )

Areq

t tt

MT

.A R Lt C D


API RP 1111 The following equations must be

satisfied:

betdt PfffP

td PP 80.0

ta PP 90.0

a)

b)

c)


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

The specified minimum burst pressure (Pb) is determined by one of the following formulae:

(1)

(2)

Where

D = outside diameter of pipe

Di = D 2t = inside diameter of pipe

S = Specified minimum yield strength of pipe

t = Nominal wall thickness of pipe

U = Specified ultimate tensile strength of pipe

For low D/t pipe (D/t < 15), formula (2) is recommended

tD

tUSP

D

DUSP

b

i

b

)(90.0

ln)(45.0

t = nominal wall thickness

Pi = pressure internal (pressure design)

Pe = external pressure

D = outside diameter

= usage factor

kt = temperature de-rating factor

S = SMYS (specified minimum yield stress)

t

ei

kS

DPPt

...2

).(


DNV 1981

DnV OS-F101

The pressure containment shall fulfill the following criteria:

3

2.

2)(, SMYS

tD

ttP sb

3

22)(,

SMTS

tD

ttP ub

( ( ( ( tptpMintp ubsbb ,, ;(

Where

(

mSC

beli

tppp

gg


Where,

pb,s(t) = Yielding Limit State

pb,u(t) = Bursting Limit Limit State

pli = Local Incidental Pressure

gSC = Safety Class Resistance Factor

gm = Material Resistance Factor


Perhitungan 2

API RP 1111

The following criteria must be satisfied:

(

( 2

3

22

12

2

v

D

t

EP

D

tSP

PP

PPP

PfPP

e

y

ey

ey

c

coio

Where

2. External Pressure Collapse

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 = Poissons Ratio (0.3 for steel)

DnV OS-F101

The following criteria must be met:

( ( t

Dfppppppp opecpcec 1

22

1

(

D

DDf

D

tSp

v

D

tE

p

o

fabp

e

minmax

2

3

1

2

1

2

Where


Where,

pc = Characteristic Collapse Pressure

pe1 = Elastic Collapse Pressure

pp = Plastic Collapse Pressure

fo = Ovality

fab = Fabrication Factor

SCm

ce

pp

gg

1.1

DnV OS-F101


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 AnalysisAs 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


Three buckling scenarios to consider :collapse - water depth where collapse can occur with negligible longitudinal stressinitiation - 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 bucklePropagating 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


Buckle during laying

Propagating BucklingCollapse pipe

Buckle during laying

Dimana :

= Longitudinal Stress (MPa)

= Hoop Stress (MPa)

= Critical Longitudinal Stress (MPa)

= Critical Hoop Stress (MPa)

= Permissible Usage Factor for Longitudinal Stress

= Permissible Usage Factor for Hoop Stress

=

BUCKLING CHECK

Local Buckling :

ycr

y

t

D s

s.

3001

xs

ys

sxcr

sycr

nxp

nyp

Based on DnV 1981

DnV 1981 (combination between internal pressure and longitudinal pressure)

1yx

xp xcr yp ycr

ss

s s

3. Local Buckling

DNV 1981

The following criteria must be satisfied:

S

A

F

M

x

AN

x

M

x

N

xx

72.0

s

s

sssa)

b)

c)

3. Local Buckling

DNV 1981

t

DS

t

DS

M

xcr

N

xcr

M

xcr

x

M

xN

xcr

x

N

xxcr

0045.035.1

20001.01

s

s

ss

ss

s

ssd)

e)

f)

3. Local Buckling

DNV 1981

(

2

2

/

3001

tD

tE

t

Dpp

tD

ycr

iey

ycr

y

s

s

s

sg)

h)

i)

1

ycryp

y

xcrxp

x

s

s

s

s

j)

3. Local Buckling

DNV 1981

Where,

x = Longitudinal Stress

xN = Longitudinal Stress (Axial)

xM = Longitudinal Stress (Bending)

xcr = Critical Longitudinal Stress

xcrN = Critical Longitudinal Stress (Axial)

xcrM = Critical Longitudinal Stress (Bending)

ycr = Critical Hoop Stress (Pressure)

3. Local Buckling

BUCKLE PROPAGATION

Propagation Buckling

Propagating pressure based on DnV 1981

2

1,15prt

p SMYSD t

Ppr > Pe ----- it is OK

kPe_max

1.15 SMYS

tnomk D

1 k

INITIATION & PROPAGATION BUCKLING

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:

2.064

0.02bit

P ED

Initiation & Propagation Buckle based on API RP 1111

4.2

24

D

tSP

PfPP

p

ppio Pp = Buckle Propagation Pressure fp = Propagating Buckle Design FactorPo = External Hydrostatic Pressure

DnV OS F101

The following equations have to be satisfied:

SCm

pr

e

fabpr

pp

D

tSp

gg

5.2

35a)

b)

Comparison Table

ASME B31.8 API RP 1111 DNV 1981 DNV OS-F101


20.6 mm 20.46 mm 21.93 mm 19.90 mm


13.80 mm 13.61 mm - 14.25 mm

Local Buckling - - 22.0 mm -

Buckle Propagation 21.68 mm 21.35 mm 23.42 mm 21.15 mm

OD = 914.4 mm; P = 15 MPa; WD = 50 100m; Content density = 200 kg/m3 ; Wave Ht = 3.8 m

Conservative one is DnV 81 & Least conservative is DnV OS-F101

SUMMARY AND CONCLUSIONS

1. 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

2. Things that have to be check in Wall Thickness Design:

Hoop stress criteria

Local Buckling check

Propagation Check

SEKIAN..

TERIMA KASIH

Kuliah-04&05 Pemilihan Material Dan Desain Tebal Pipa

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