comparison dnv standards 504

Proceedings of the Sixth AEESEAP Triennial Conference Kuta, Bali, Indonesia, August 23 – 25, 2000

162 2000 AEESEAP

COMPARISON OF SOME STANDARDS FOR SUBMARINE PIPELINE

Gde Pradnyana, Adang Surahman, Ardianto Saputro

Offshore Technology Research Group Inter University Research Center for Engineering Sciences (IURC-ES)

Institut Teknologi Bandung, Indonesia

ABSTRACT

DNV Standard on submarine pipeline, de facto, has become an international standard beside the API RP5L. Technically the DNV standard has been used worldwide as guidance to design submarine pipeline, while the API RP5L is more emphasizing the material aspect than pipeline design guideline against environmental loading. DNV 1981 (which was an up-date of DNV 1976) was developed based on Working Stress Design (WSD) concept, where the applied load is the design load (which is normally factored-up from the actual condition) while assumed strength is the allowable strength (normally factored-down from the actual strength Based on these two sides of the equation then a safety factor is obtained, which according to DNV 1981, for example should be more than 1.1 (for on-bottom stability). Similarly with the analysis against buckling where the safety factor is implied in term of permissible usage factor. Selection of those factors commonly conducted based on “engineering justification” where risk inherited in those factors has not been fully taken into account. This method also implied “double safety factor”. With the introduction of the Load and Resistance Factor Design (LRFD) concept as adopted by the DNV 1996 (which is currently being revised into DNV 1999), the load and the resistance factors are selected by considering the acceptable risk consequences. A high-pressure gas pipeline going through heavily populated area will obviously bear higher risk than water pipe passing through the same area. Apart from risk related to “personnel safety”, it may also be related to the environmental damage caused by any failure in the pipeline. DNV 1996 has introduced a 3x3 matrix to classify the risk into low, medium, and high. Development of the LRFD concept was not conducted without taking the WSD as its benchmark. Many offshore production facilities (including pipelines) have been successfully designed using WSD concept. The back draw of this old concept is that it does not have consistence reliability level. Unlike the WSD, selection of the LRFD factors will consider the level of uncertainty (bias) of the load and the resistance. Therefore facilities designed for a less predictable load (or environmental condition) will have to use higher load factor, similar consequence for the resistance factor. Environmental condition in Indonesia is probably more predictable than in the North Sea (where the DNV was initially designed for), therefore the load factor should probably be smaller than those in the North Sea or in the Gulf of Mexico. Apart from understanding the loading uncertainty, attention should also be put on the bias of resistance. This is important to investigate the quality level (i.e. reliability of the resistance) of the pipeline (produced in Indonesia in comparison with those imported from abroad) such that the designers, contractors, and the operators would be able to take the most advantage of the LRFD concept.

I. INTRODUCTION

DNV has a long track record in offshore pipelines. The first 'Rules for Submarine Pipelines and Pipeline Risers' code was issued in 1976, and with a revision in 1981, has been extensively used on offshore pipeline projects worldwide. Over the years, however, much technical progress has taken place in pipeline design, materials, fabrication and installation, as well as in the operation of offshore pipelines. These developments have not necessarily been implemented in the code, in which few updates have been made compared to code development

Comparison of Some Standards....... Gde Pradnaya, et.al.

163

in other industries. The pipeline industry has in recent years experienced a growing focus on cost reduction, resulting in innovative design approaches and optimized construction methods.

In 1996, DNV was again first with a major update implementing a limit-state design philosophy with calibrated partial safety factors. This was a giant step to take in an industry recognized for being rather conservative, but it has shown to be the only way to go to meet the challenges the industry is facing. We are seeing new design scenarios not covered by earlier standards and codes. Examples are greater water depths (the governing design case goes from internal pressure to external pressure), new materials, new installation methods, uneven seabed, higher temperatures and pressures. In addition, changes in the regulatory framework in several countries have imposed requirements for the implementation of safety concepts and risk assessment. The new regulation (DNV 1996) using principal design base on limit state and reliability, beside that, there is design approach who more flexible and consistent safety factor. The purposes of this new regulation are: • To fulfil the requirement as basic philosophy and regulation when used as DNV certification for

submarine pipeline system, and explain minimum design for fabrication, installation, operation and re-qualification and another things who concern with certification

• To accommodate international security standard who concern the strength and performance of submarine pipeline system.

• As a reference of technical document for contractual problem between client and contractor, or between contractor and sub-contractor.

The new design philosophy in the 1996 standard allows for a more flexible design approach where those investing more in increased knowledge about their design, improved materials and procedures are allowed to take advantage of this when setting the acceptance criteria. The limit-state methodology being used will also give a consistent safety level for all limit states (i.e. all failure modes will have the same failure probability). The 1996 revision of the pipeline standard also incorporates results from numerous research projects and extensive accumulated operational experience. As a result, the 1996 pipeline standard can be used both as a guidance covering design scenarios relevant for deepwater application and to perform cost optimization with due consideration to safety and reliability. DNV has received a lot of feedback from projects using the ‘96 Pipeline Rules. Part of this has been constructive proposals on improvements and further enhancement and developments. All this feedback has triggered a project on an update of the 1996 standard. The updating work is aiming at issuing a revised pipeline standard in the third quarter of 1999. The changes being made are mainly focused on clarifications and simplifications to account for the fact that there is limited experience in using limit-state design methods and a lack of "rule of thumb". Requirements to line-pipe testing have been modified and there have been given a clearer link between design and material requirements. Supporting guidelines and recommended practices, several Guidelines and Recommended Practices are being developed and linked up to the design philosophy in the standard. Two guidelines have recently been issued, one covering guidance in how to handle interference between trawl equipment and pipelines and the other covering vortex shedding induced vibrations of pipeline spans. Other guidelines are under development and will be issued in the near future, and more are planned. The ones under development cover residual strength of corroded pipelines, high pressure and high temperature pipelines (buckling and mitigation), S-lay installation at deepwater pipelines and reeling installation of pipelines.

II. COMPARISON OF SOME REGULATIONS

A summary of the required wall thickness for each limit state and condition is given in Figure 1. The values are compared with corresponding values given by the old Pipeline Rules, DNV’81. The wall thickness given by DNV’96 is, in general, slightly lower than the corresponding


164

from DNV’81. The major difference is in Safety Class High (zone 2) for the hoop stress criteria, where the allowed utilization is considerably lesser in DNV’81. This difference is not, however, reflected in the final design since the installation is governing in Safety Class High.

16.8

15.4 15.4

13.9

18.216.8

18.2

15.27 14.7515.45

12.88 12.88

8.05

15.27 15.45

02468

101214161820

Bucklin

g, ins

tallat

ion

Bucklin

g, op

eratio

n, SCN

Bucklin

g, op

eratio

n, SCH

Hoop,

SCN

Hoop,

SCH

Hoop,

Pressu

re tes

t

Govern

ing W

all th

ickne

ss

Safety

Class N

ormal

Safety

Class H

igh

Limit State/ Condition

Wal

l thi

ckne

ss (m

m)

DNV'81

DNV'96

FIGURE 1. COMPARISON OF DESIGN USING DNV 81 AND DNV 96

DNV 1999 is revision of DNV 1996, and there is a few significant changes from DNV 1996. With considering this matter, we can describe comparison of DNV 1981, DNV1996, DNV 1999 and DNV 1999 (revision) became two big parts. First, we will discuss about the differences between DNV 1981 and DNV 1996. Second, we will discuss about the differences between DNV 1996, DNV 1999, and DNV 1999 (revision). 2.1. General Comparison between ASME B31.8 and DNV 1996

General comparison between ASME B31.8 and DNV 1996 can be describe with following, like:

TABLE 1. GENERAL COMPARISON BETWEEN ASME B31.8 AND DNV 96

2.2. Comparison between DNV 1981 and DNV 1996

At the new regulation (DNV 1996), there are same additional explanations at the certain item, like:

No

ASME B31.8

DNV 96

1 •Allowable Stress Design only

•Limit State Design. Consistent Target Safety Level. Strain based design allowed

2 •Hoop Stress t=PD/2SET based on yielding. F=0.50 - 0.72 (Zone 2,1)

•Hoop Stress t based on bursting and yielding Limit State. hyield = 0.93 - 0.88 (Low - High) Fatigue, Buckling formulation given.

3 •Other stress criteria for longitudinal and combined stresses

•Pressure test 1.15 - 1.20 Pd Strength (2 hrs) and 1.09 - 1.14 Pd Leak (24 hrs)

4 •Pressure test 1.25 x Pd (24 hours) •Partial Safety Factors based on choice of Line pipe Quality Levels. Reliability Analyses allowed in lieu of recommended factors.

5 •Safety factors based on API 5L criteria •Applicable only for submarine pipeline steels including clad and stainless steel. Modern TMCP steels are considered

6 •Applicable also for pipelines of other materials e.g. cast iron, plastic pipe etc.

•Suitable for offshore and submarine pipeline

7 •Suitable for onshore pipeline distribution system but less so for offshore pipelines. (1 chapter on offshore pipelines).

•Criteria in line with specifications of major offshore operators. Harmonized with ISO standards on pipeline.


165

• DNV 1996 refer to more regulations and more design reference. • DNV 1996 apply quality assurance in the design, construction and pipeline operation system to

comply with ISO9001 • DNV 1996 discuss more detail for certification and documentation of fabrication, construction,

and installation, until operation phase. • DNV 1996 give additional consideration of line pipe that will be used. In the other hand, this

regulation notice about type of material in this line pipe for on bottom stability of the pipe. • In case of loading, DNV 1996 using load factor and load combination. In classification of

loading, accidental load became new item, and there is additional item of loading in DNV 1996, constructional load

• DNV 1996 discuss about the use and the need of material more specific, and also discuss about new material where we weren’t found at DNV 1981.

• DNV 1996 give some design criteria layout of pipeline system. ∗ Pipeline shouldn’t near with another structure or another pipeline system ∗ The crossing pipeline must be separate with minimum vertical distance 0.3 m ∗ The riser must be protected from impact load, the protection can be done by:

- Assembly structure protection - Concern about riser location in the structure - Choosing right location of the boat landing

∗ The pipeline system must be protected from mechanic interaction, the protection can be done by: - Using Concrete coating - Pipe burial - Heaped the pipeline with material such as, sand and gravel.

• DNV 1996 completing discussion on DNV 1981 about riser support. This regulation discussed more specific about riser connection at the structure, such as welding, doubler, and gusset plate.

• Concrete coating design on DNV 1996 refer to ISO9004 • DNV 1996 introduce new material for cathodic protection need, and discuss more detail about

concrete coating criteria. • DNV 1996 refer to Engineering Critical Assessment (ECA) to verification of whole pipeline

design Principal difference between old regulation (DNV 1981) and new regulation (DNV 1996) is the method of design calculation. DNV 1981 still using Work Stress Design Method (WSD), whereas DNV 1996 using Load Resistance Factor Design (LRFD). That is way we will get different result of design when we try to compare applying design using DNV 1981and DNV 1996. These differences can be seen clearly from the following Table 2:

TABLE 2. COMPARISON OF DESIGN USING DNV 81 AND DNV 96

DNV 1981 DNV 1996 !" The strength criteria based on allowable

stress. Limit state method also can be applied with preparing factor from loading and material.

!" The design criteria in these requirements are based upon the limit state methodology. As an alternative to the local buckling check a traditional Allowable Stress Design format is provide in case of internal over pressure

!" A whole design of pipeline system guarantee with using separate safety factor base on LRFD concept

!" In this regulation there is no limitation of water depth in designing

!" Hoop stress calculation :

tFhyp k..σησ = , or

.hη = usage factor

typσ = permissible hoop stress

tFσ = Specified minimum yield strength

!" Hoop stress calculation:

( )t

tDpp eiy 2. −−=σ

D = nominal outside diameter .t = nominal wall thickness ( depend on what calculation for)

!" The accumulated plastic strain increments are to be calculated from the point where the material stress strains curve deviated from a linear relationship.

!" The pipe wall force is to be consistent with the effective axial


166

tk = temperature factor, (for t<120oC =1.0)

( )t

Dpp eiy 2.−=σ

D = nominal outside diameter .t = nominal wall thickness

force that satisfies external equilibrium of the considered pipe section.

( ) 22

42

4DptDpNS ei

ππ +−−=

N = pipe wall force (true axial force) S = effective axial force (tension is positive)

!" Buckling occurrence: - Local Buckling (pipe wall buckling) - Propagation buckling

!" Buckling occurrence: - Local Buckling (pipe wall buckling) - Global Buckling (euler buckling), buckling of the pipe as a bar

in compression !" The critical combination of longitudinal and

hoop stresses may be expressed as follow :

1=+

ycr

y

xcr

x

σσ

σσ

α

Mx

Nxx σσσ +=

ANN

x =σ

WMM

x =σ

=N axial force

( )ttDA .−= π = cross sectional area

=M bending moment

( ) ttDW .4

2−= π= section modulus

Mxcr

x

MxN

xcrx

Nx

xcr σσ

σσσσσ +=

=Nxcrσ critical longitudinal when N is acting

alone (M = 0, p = 0)

FN

xcr σσ = ; 20≤tD

−−= 20001.01

tD

FN

xcr σσ ;

10020 << tD

=Fσ specified yield strength (corresponding to 0.2 % residual strength)

=Mxcrσ critical longitudinal (when determined

as M/W when M is acting alone (N = 0, p = 0)

−=

tD

FN

xcr 045.01σσ

ycr

y

tD σσ

α .3001+=

=ycrσ critical hoop stress when p is acting

alone (N = 0, M = 0)

FyEyEycr tDtE σσσσ

32;

2

≤

−==

!" The buckling capacity checks are separate for load controlled and displacement controlled conditions:

!" Load controlled condition:

1...

22,, ≤

+

+

Rc

e

Rc

CEECFCF

pp

MMM

γγγγγ

!" Displacement controlled condition:

1...

18.0,, ≤

+

+

Rc

e

Rc

CEECFCF

ppγγε

εγεγγ

!" Load factor and load combination

Limit State

LoadComb. id

SLS &ULS

a

b

FLS

ALS

FunctionalLoads

γγγγ F

1.2

1.1

1.0

1.0

EnvironmentalLoads

γ γ γ γ E

-

1.3

1.0

1.0

AccidentalLoads

γγγγ A

-

-

-

1.0

!" Condition Load Factor

Condition

Uneven Seabed

Deformation Governed

Pressure Test

Otherwise

γγγγ C

1.07

0.82

0.91

1.00

cFM , = characteristic functional bending moment

cEM , = characteristic environmental bending moment

cM = characteristic limit bending moment

Mpc fMM .= ; 15 < D/t < 45

tDSMYSM p .. 2=

−

−

+

−=

2

,,2

..431

.21..

.2

cos...431

SMYS

MNN

SMYSf

hF

Rc

CEECFF

hFM

σγ

γγγγπ

σγ

+=

Rc

CEECFFM M

NNf

γγγπ ,, ..

.2

cos ; for 0≥hσ

cFN , = characteristic functional axial pipe wall force

cEN , = characteristic environmental axial pipe wall force


167

FyEyE

FFycr σσ

σσσσ

32;

32

311

2

>

−=

The permissible combination may then be expressed as :

1..

≤+

ypycr

y

xpxcr

x

ησσ

ησσ

α

Permissible usage factor for general case:

notes :

- for pipeline during operation, multiple by 1.2 - for pipeline during installation, multiple by 1.44

!" Propagation Buckling: Propagation pressure :

2

.15.1

−≈

tDtP Fpr σπ

cF ,ε = characteristic functional bending strain

cE ,ε = characteristic environmental bending strain

cM ,ε = characteristic limit bending strain

gwh

cM EDt ασε ..501.0,

+−= ; 15 <D/t< 45 ;

0≥hσ

−= 01.0, D

tcMε ; 15 <D/t< 45 ;

0≤hσ

ResistanceFactor

MaterialRequirement

Normal

FullfillingC311

γγγγ R

γγγγ εεεε

γγγγ R

γγγγ εεεε

Low

1.24

2.10

1.19

2.00

Normal

1.37

2.60

1.32

2.50

Medium

1.58

3.50

1.52

3.30

Safety Class

eP = characteristic external over-pressure

cP = characteristic Collapse pressure

≤

R

ce

ppγ1.1

!" Propagation Buckling: Propagation pressure :

5.2

..26

=

DtSMYSPpr

!" Allowable stress design format 222 .3. lhihlhe τσσσσσ +−+=

=eσ equivalent stress

=hσ hoop stress

=iσ longitudinal stress

=lhτ tangential shear stress

( )tFepepe k..σησσ =<

=epη usage factor :

!" Allowable stress design format 222 .3. lhihlhe τσσσσσ +−+=

=eσ equivalent stress

=hσ hoop stress

=iσ longitudinal stress

=lhτ tangential shear stress

SMYSe .ησ ≤

SMYSl .ησ ≤

=η usage factor :

2.3. Comparison between DNV 1996, DNV 1999 and DNV 1999 (revision)

Globally, the differences between DNV 1996 and DNV 1999 can be written as following items: • DNV 1999 refer to more regulations and more design reference.


168

• DNV 1999 explain that design pressure can be assumed as internal pressure, and start propose design need for earthquake problem. There is additional load factor in DNV 1999 (see Table 3.)

• There is some modification of DNV 1999, such as shown in the following item: ∗ Additional some thing, like:

How to give consideration of temperature limit of a material. Plastic strain calculation Reducing Yield strength due UOE process

∗ Format of LRFD method has been modified. Resistance factor has been combine to became material factor and safety class factor.

∗ Equation of pressure containment has been modified with considering effect from reducing incidental pressure. Then, usage factor in the safety zone decrease to 0.67 and 0.7

∗ Local buckling criteria have been modified. Displacement controlled capacity to conservative for D/t less than 20-22.

∗ Limitation for plastic strain criteria has been modified became 0.3% (reducing 0.5%) • In the part which discuss about line pipe, the different on DNV 1999 can be seen in the

following item: ∗ Chemical composition need become function of production process material strength. ∗ Fracture arrests need as a function from thickness and diameter ∗ Re evaluated testing frequency ∗ Introduce level test confirmatory, level above SMYS, CVN, and rigidity, where frequency

of test must be added ∗ Redefine concept of material quality level ∗ DNV 1999 introduce philosophy from pipe testing. Summation of test and test factor k

proposed to assure that there is no pipe who have unacceptable properties when its deliver from laboratory. Summations of test, pipe properties tested, and reanalysis the best k factor become a basic and will be the subject of reliability analysis before fixed.

∗ Discussion about “INSTALLATION” on DNV 1999 is more specific. Table 3, shows the comparison of design using DNV 1996, DNV 1999 and DNV 1999 (revision) on Design Philosophy while Table 4 is the comparison on loading. Table 5 shows the comparison on Limit State. III. COMPARISON APPLICATION OF SOME REGULATION

For this purpose, we use this example of pipeline system for application of some regulation. The result is shown in Table 6.


169 2000 AEESEAP

TABLE 3. COMPARISON OF DESIGN USING DNV 1996, DNV 1999 AND DNV 1999 (REVISION) ON DESIGN PHILOSOPHY

DNV 1996 DNV 1999 DNV 1999 (revision)

Same thing with DNV 1999(a)

!"Partial Safety factor Methodology

- ( ) ( )RcdccEEcFFd RRSSS γγγγ ≤,.,. ,,


- ( ) ( )RcdccEEcFFd RRSSS γγγγ ≤,.,. ,,


- ( )

≤

mSC

kdccEEcFFd

RRSSSγγ

γγγ.

,.,. ,,

!"Acceptable failure probability:

!"Acceptable failure probability (Same thing with DNV 1996

!"Acceptable failure probability:


170

TABLE 4. COMPARISON OF DESIGN USING DNV 1996, DNV 1999 AND DNV 1999 (REVISION) ON LOADING

DNV 1996 DNV 1999 DNV 1999 (revision) !" !" !"Earthquake; Load effect by earthquake, either directly

or indirectly, shall be classified into accidental or environmental loads depending on its probability of occurrence. Return periods larger than 10-4, 10-5, and 10-6 can be disregarded for safety classes low, Normal and High, respectively.

!"Load factor and load combination

Limit State

LoadComb. id

SLS &ULS

a

b

FLS

ALS

FunctionalLoads

γγγγ F

1.2

1.1

1.0

1.0

EnvironmentalLoads

γ γ γ γ E

-

1.3

1.0

1.0

AccidentalLoads

γγγγ A

-

-

-

1.0

!"Load factor and load combination

Limit State

LoadComb. id

SLS &ULS

a

b

FLS

ALS

FunctionalLoads

γγγγ F

1.2

1.1

1.0

1.0

EnvironmentalLoads

γ γ γ γ E

0.7

1.3

1.0

1.0

AccidentalLoads

γγγγ A

-

-

-

1.0

!"(Load factor and load combination and Condition load factor are same as DnV 1999(a)

Design Load, Ld : EECFFd LLL γγγ ... +=

Design Resistance, ( )

msc

kkd

fRRγγ .

=

=mγ 1.15 (for SLS, ULS, and ALS) = 1.00 (for FLS) safety class Low Normal High =scγ 1.04 1.14 1.30


171

TABLE 5. COMPARISON OF DESIGN USING DNV 1996, DNV 1999 AND DNV 1999 (REVISION) ON LIMIT STATE

DNV 1996 DNV 1999 DNV 1999 (revision) !"Effective axial force of a totally restrained pipe in the

linear elastic stress range due to pressure and temperature is if it can be idealized as thin-walled:

( ) αν ....21.. TEAApHS sii ∆−−∆−=

!"Effective axial force of a totally restrained pipe in the linear elastic stress range due to pressure and temperature is if it can be idealized as thin-walled:

!" ( ) TEAApHS sii ∆−−∆−= ...21.. ν

!"Effective axial force of a totally restrained pipe in the linear elastic stress range due to pressure and temperature is if it can be idealized as thin-walled:

!" ( ) αν ....21.. TEAApHS sii ∆−−∆−= !" !" !"Characteristic yield strength fy = SMYST.αU.

!"Characteristic tensile strength fu = SMTST.αU. !".αU.= 0.96 for normal condition ; and αU.= 1.0 for

suplementary condition !" !"fabrication reduction factor αfab :

- for seamless : 1.00 - for UO & TRB process : 0.93 - UOE process : 0.85

!"fabrication reduction factor αfab : - for UO process : 0.925 - UOE process : 0.85

!"Flow diagram for structural design

!"Flow diagram for structural design

!"Flow diagram for structural design (same with DnV 1999a)


172

Start

Pressurecontainment

LocalExternal

overpressure

Externaloverpressure

Propagating

Global

Fatigue

Ovality

Misscelaneous

Final Design

Displ.controlled

Internaloverpressure ASDDispl.

controlled

Only LoadControlled design

applied

Accumulatedplastic strain

Fracture

Ok?no no

yes

legend :

Start

Pressurecontainment

Pc

Systemcollapse

Mc, yMc, wMc, f

Interaction Displ.controlled

ec, M

Interaction

ep < 0.3 %

E C A

ep < 2 %

Supplementaryrequirement P

PropagatingBuckling

Supplementaryrequirement P

Fatigue

Ovality

Misscelaneous

Final Design

Ok?

no no

yes

legend :


173

!"Pressure Containment (Bursting) The usage factor in this sub-section can be applied provided that the maximum internal pressure at any point has a low life time probability of exceeding the local incidental Pressure.

!" [ ]SMTSSMYS USh .,.min ηησ ≤

The following additional conditions are fulfilled:

- The pipe material is quality level I or II - SMYS < mean – 2 σ - SMTS < mean – 3 σ - Necessary CTOD value requirements for HAZ and

weld metal are establish that are relevant for the specific design condition and with the regard to type the extent of longitudinal weld defects likely to exist.

!"The pressure containment criteria may alternatively be expressed in an LRFD format as follow

- Bursting Limit State : ( )SMTSUhinc .1.1.. ησγ ≤

- Yielding Limit State : ( )SMYSShinc .1.1.. ησγ ≤

- =incγ 1.05 – 1.1

!"For pressure containment shall fulfill the following criteria : - Yielding Limit State (SLS) :

( ) '.2.1

1 SMYStD

tpp Seldp ηγ−

≤−

- Bursting Limit State (ULS) :

( ) '.2.1

1 SMTStD

tpp Ueldp ηγ−

≤−

!"For pressure containment, the pressure load effect

factor shall be determined by : i

dp p

p1.1=γ

pγ value are:

- For normally cond. (pinc < 1.10 pd) , pγ = 1.00

- For minimum cond. (pinc < 1.05 pd) , pγ = 0.96

- For full shut in-pressure (pinc = 1.0 pd) , pγ = 0.91

- For system pressure test, pγ = 1.00

!"The local test pressure (plt) at any point in the pipeline

system shall fulfill the following requirement.

- Normal and High Safety Class : lilt pp 05.1≥

- Low Safety Class : lilt pp 03.1≥ The local incidental pressure can be expressed as :

ghpp contdli ρ+=

!"The pressure containment shall fulfill the following criteria. - Yielding Limit State (SLS) :

( )3.

22.1

1

msc

yeldp

ftD

tppγγ

γ−

≤−

- Bursting Limit State (ULS) :

( ) ( ) 315.1.22.

1

1

msc

ueldp

ftD

tppγγ

γ−

≤−

!"For pressure containment, the pressure load effect

factor shall be determined by : ppin

p =γ

pγ value are:

- For normally cond. (pinc = 1.10 pd) , pγ = 1.10

- For minimum cond. (pinc < 1.06 pd) , pγ = 1.60

- For full shut in-pressure (pinc = 1.0 pd) , pγ = 1.0

- For system pressure test, pγ = 0.97

!"The local test pressure (plt) at any point in the pipeline

system shall fulfill the following requirement.

- Normal and High Safety Class : lilt pp 05.1≥

- Low Safety Class : lilt pp 03.1≥


174

The local incidental pressure can be expressed as : ghpp contdpli ργ +=

!"The buckling capacity checks are separate for load controlled and displacement controlled conditions : - Load controlled condition :

1...

22,, ≤

+

+

Rc

e

Rc

CEECFCF

pp

MMM

γγγγγ

- Displacement controlled condition :

1...

18.0,, ≤

+

+

Rc

e

c

CEECFCF

ppγγε

εγεγγ

ε

cFM , = characteristic functional bending moment

cEM , = characteristic environmental bending moment

cM = characteristic limit bending moment

Mpc fMM .= ; 15 < D/t < 45

tDSMYSM p .. 2=






gwh


+−= ;15<D/t< 45;

0≥hσ

−= 01.0, D

tcMε ; 15<D/t< 45 ;


1...

22,, ≤

+

+

Rc

e

Rc

CEECFCF

pp

MMM

γγγγγ


1...

18.0,, ≤

+

+

Rc

e

c

CEECFCF

ppγγε

εγεγγ

ε

The moment capacity is to be calculated as :

Mpc fMM .= ; 15 < D/t < 45

tDSMYSM p .. 2=

−

−

−=

2

2

.431

.21

2cos...

431

SMYS

SMYSNN

aSMYS

f

C

h

h

p

C

c

CF

hFM

ασ

σγγπσγ

( )SMYSSMTS

C ββα ++= 1


122

∆+

∆−+

pc

d

pc

d

pc

dmSC

cc

dmSC P

PPP

MM

SS

αααγγ

αγγ


22

∆+

+

cc

ddmSC

cc

ddmSC

cc

ddmSC p

pS

SS

Mα

γγα

γγα

γγ


( ) 22

2 .ttDfMc −=

( )y

uC f

fββα +−= 1

( )hq+= 4.0β ; 15/ <tD

( )( ) 45/604.0 tDqh −+=β ;

60/15 ≤≤ tD

0=β ; 60/ >tD Strain capacity at maximum moment :


175

0≤hσ

ResistanceFactor

MaterialRequirement

Normal

FullfillingC311

γγγγ R

γγγγ εεεε

γγγγ R

γγγγ εεεε

Low

1.24

2.10

1.19

2.00

Normal

1.37

2.60

1.32

2.50

Medium

1.58

3.50

1.52

3.30

Safety Class


Mpc fMM .= ; 15 < D/t < 45

tDSMYSM p .. 2=

−

−

+

−=

2

,,2

..431

.21..

.2

cos...431

SMYS

SMMNN

SMYSf

hF

F

Rc

CEECFF

hFM

σγ

γγγγπ

σγ

+=

Rc

CEECFFM M

NNf

γγγπ ,, ..

.2

cos ; for 0≥hσ






Strain capacity at maximum moment :

gwh


+−= ; 15 <D/t< 45 ;

0≥hσ

=β 0 ; 20/ <tD

( ) 40/20−= tDβ ; 60/20 ≤≤ tD

1=β ; 60/ >tD Strain capacity at maximum moment :

gwhh

cM SMYSDt αασε .5121 5.1

2

,

+

= ;

15<D/t<60

gwhy

hcM fD

t αασε .5101.078.0 5.1,

+

−=


176

−= 01.0, D

tcMε ; 15 <D/t< 45 ;

0≤hσ !"The buckling propagating pressure is to be taken as:

5.2

..26

=

DtSMYSppr

!"The buckling propagating pressure is to be taken as: 5.2

..26

=

DtSMYSp fabpr α

!"The buckling propagating pressure is to be taken as: 5.2

...

.35

=

Dtf

pSCm

fabypr γγ

α

!"The fatigue criterion is given by :

∑=

≤=k

ifat

i

ifat N

nD1

α

For pipeline system with no access, 1.0=fatα

For pipeline system with access, 3.0=fatα


∑=

≤=k

ifat

i

ifat N

nD1

α

For pipeline system with no access, 1.0=fatα

For pipeline system with access, 3.0=fatα


∑=

≤=k

ifat

i

ifat N

nD1

α

For low safety class, 3/1=fatα



!"The flattening define as

02.0minmax ≤−=D

DDfo


02.0minmax ≤−=D

DDfo


03.0minmax ≤−=D

DDfo

!"The range of the plastic strain criteria : εP ≥ 0.5 % !"The range of the plastic strain criteria : εP ≥ 0.3 % !"The range of the plastic strain criteria : εP ≥ 0.3 %


177

TABLE 6. EXAMPLE OF PIPELINE SYSTEM FOR APPLICATION OF SOME REGULATION..

Pipe Data DNV 1981 DNV 1996 DNV 1996 (2) DNV 1999 DNV 1999 (2) DNV 1999 (rev.) DNV 1999 (rev.) (2) Outside Diameter D 6inch 6inch 6 inch 6 inch 6 inch 6 inch 6 inch Nominal Thickness tnom 0.625inch 0.575inch 0.625 inch 0.625 inch 0.625 inch 0.575 inch 0.625 inch Internal Pressure pd 15.5bar 15.5bar 230 bar 15.5 bar 125 bar 15.5 bar 450 bar External Pressure pe 4.474bar 4.474bar 4.474 bar 4.474 bar 4.474 bar 4.474 bar 4.474 bar Safety Index � 21.410 21.102 21.410 21.410 21.410 21.102 21.410 Compared Parameter Pc 9.657543 10.53309 10.53309 10.53309 9.65754 10.53309 Parameter 0.000816~0 0.000504 ~0 0.000504 ~0 0.000504 ~0 0.003612 ~0 0.000504 ~0 Pressure Containment Bursting Limit 0.021136<1 ==> Ok! 0.389075 <1 ==> Ok! 0.019022 <1 ==> Ok! 0.20793 <1 ==> Ok! 0.017829 <1 ==> Ok! 0.648368 <1 ==> Ok! Yielding Limit 0.022746<1 ==> Ok! 0.418711 <1 ==> Ok! 0.020471 <1 ==> Ok! 0.223768 <1 ==> Ok! 0.019068 <1 ==> Ok! 0.693421 <1 ==> Ok! Installation Load Controlled > Load Combination (a) 0.9701<1 ==> Ok! 0.8969<1 ==> Ok! 0.900085 >1 not Ok! 0.951898 <1 ==> Ok! 0.997731 >1 not Ok! 0.976251 <1 ==> Ok! 0.93956 >1 not Ok! > Load Combination (b) 0.8343<1 ==> Ok! 0.995906<1 ==> Ok! 0.984322 >1 not Ok! 0.844259 <1 ==> Ok! 0.888937 >1 not Ok! 0.953171 <1 ==> Ok! 0.995417 >1 not Ok! Displacement Controlled > Load Combination (a) 0.099262<1 ==> Ok! 0.092077 <1 ==> Ok! 0.063708 <1 ==> Ok! 0.243134 <1 ==> Ok! 0.09 <1 ==> Ok! 0.08 <1 ==> Ok! > Load Combination (b) 0.124281<1 ==> Ok! 0.115308 <1 ==> Ok! 0.065428 <1 ==> Ok! 0.244855 <1 ==> Ok! <1 ==> Ok! <1 ==> Ok! Operation Load Controlled > Load Combination (a) 0.0386<1 ==> Ok! 0.002093<1 ==> Ok! 0.002223 <1 ==> Ok! 0.002118 <1 ==> Ok! 0.053 <1 ==> Ok! 0.03109 <1 ==> Ok! 0.93956 >1 not Ok! > Load Combination (b) 0.0277<1 ==> Ok! 0.00224<1 ==> Ok! 0.002378 <1 ==> Ok! 0.001949 <1 ==> Ok! 0.05282 <1 ==> Ok! 0.001287 <1 ==> Ok! 0.995417 >1 not Ok! Displacement Controlled > Load Combination (a) 0<1 ==> Ok! 0 <1 ==> Ok! 0.028173 <1 ==> Ok! 0.2272 <1 ==> Ok! 0.0081 <1 ==> Ok! 0.0075 <1 ==> Ok! > Load Combination (b) 0<1 ==> Ok! 0 <1 ==> Ok! 0.028173 <1 ==> Ok! 0.2272 <1 ==> Ok! <1 ==> Ok! <1 ==> Ok! Notes : First column of DNV 1996 is calculation result with optimizing wall thickness, second column of DNV 1996 is calculation result with optimizing internal pressure, and so do with DNV 1999 and DNV 1999 (rev.)


178 2000 AEESEAP

IV. CONCLUSION

The Rules are based upon the limit state methodology, using a Load and Resistance Factor Design (LRFD) format, with calibrated partial safety factors. A modern safety philosophy has been incorporated in the rules by introduction of the “safety class” concept. The two major advantages with the new rules and the LRFD format are: • Flexibility, not restricting the user to traditional design • Consistent safety level Further, recent research results and project experience have been included in the Rules, also allowing for: • New installation methods • New material Through the structure of the Rules; limit states, load factors, condition factors and resistance factors, further improvement and extension gained through new research and experience is made possible. From a couple existing pipeline design, it has been try to do re-calculation using DNV 1981, DNV 1996, DNV 1999, and DNV 1999 (revision). Recalculation has been done with optimizing wall thickness (where Internal pressure kept constant), and optimizing internal pressure (where wall thickness kept constant). The results show that with using DNV 1996, DNV 1999 and DNV 1999(revision), we can reduce pipeline wall thickness, and we can get the most reduce in wall thickness when we use DNV 1999(revision). And we can also raising the ultimate internal pressure with using DNV 1996, DNV 1999 and DNV 1999(revision).

REFERENCES [1] DNV, DNV Rules for Submarine Pipeline Systems, Det Norske Veritas, Norway, 1981. [2] DNV, DNV Rules for Submarine Pipeline Systems, Det Norske Veritas, Norway, 1996. [3] DNV, DNV Rules for Submarine Pipeline Systems, Det Norske Veritas Norway, 1999 [4] Collberg, Leif, “An Introduction to the DNV 1996 Rules for submarine Pipeline Systems”,

ISOPE’97-TB-02. [5] Bjomsen, Tommy, “Offshore Gas Pipeline Application of New Codes”, APIA Offshore

pipeline Seminar – , Perth, 22 & 23 April 1997. [6] Dela Mare,R.F, Advances in Offshore Oil & Gas Pipeline Technology. [7] McAllister, E. W, Pipeline Rules and Thumb Handbook.

comparison dnv standards 504

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