Parametric Study Of Offshore Pipeline Wall Thickness By .
한국해양공학회지 제26권 제2호, pp 1-7, 2012년 4월 (ISSN .001Parametric Study of Offshore Pipeline Wall Thickness byDNV-OS-F101, 2010Han-Suk Choi*, Su-Young Yu*, Dae-Hoon Kang** and Hyo-Dong Kang***Graduate School of Engineering Mastership, Postech, Pohang, Korea**Daewoo Shipbuilding & Marine Engineering Co., Seoul, KoreaKEY WORDS: Offshore pipeline wall thickness, Pressure containment, Collapse, Propagation buckling, Load controlled condition,Displacement controlled conditionABSTRACT: DNV-OS-F101 includes the concept development, design, construction, operation,and abandonment of offshore pipeline systems. Themain objective of this offshore standard (OS) is to ensure that pipeline systems are safe during the installation and operational period. The pipelinedesign philosophy also includes public safety and environmental protection. The mechanical wall thickness design of a pipeline shall follow thedesign objectives and safety philosophy. This new design code includes a very sophisticated design procedure to ensure a safe pipeline, public safety,and environmental protection. This paper presents the results ofa parametric study for the wall thickness design of offshore pipelines. A designmatrix was developed to cover the many design factors of pipeline integrity, public safety, and environmental protection. Sensitivity analyses of thevarious parameters were carried out to identify the impacts on offshore pipeline design.1. 서론the offshore pipeline design. A design matrix was developedto include many design factors of pipeline integrity, publicsafety, and environmental protection with a consistent designmethodology. Parametric sensitivity analyses were carried outto identify the impacts on the offshore pipeline wall thicknessDet Norske Veritas (DNV) published the offshore pipelinedesign rules (DNV, 1976; DNV, 1981). These design ruleswere based on the working stress design and have been usedover two decades. In the year 2000, DNV published firstdesign. Various results of the parametric study are presented.offshore standard (OS) DNV-OS-F101 for the design of theoffshore pipeline systems with limit states or load and resistance factor design (LRFD). This offshore standard has been2. Safety, Concept Development and DesignPremisecontinuously updated based on various joint industry projectsand many offshore installations (DNV, 2000, 2005, 2007, 2010).This new design code covers the all aspects of offshore pipe-An overall safety philosophy is applied in the conceptdevelopment, design, construction, operation and abandon-line system including concept development, design, construction, operation and abandonment at the end of productionlife. The main objective of this offshore standard is to ensurement of pipelines. DNV-OS-F101 defines two integrity stages:establishment of integrity in the concept development, designand construction phases; and maintaining integrity in thethat pipeline systems are safe during the design life. Pipelinedesign philosophy also includes the public safety and environmental protection. Mechanical wall thickness design of aoperating phases. The integrity of the offshore pipelinesystem is ensured through safety philosophy integrating witheach of the different parts such as safety objective, systematicpipeline shall be followed by the design objectives and safetyphilosophy. This new design code includes a very sophisticated design procedure to ensure pipeline safety, public safetyreview, safety class methodology and quality assurance.An overall safety objective shall be established, plannedand implemented, covering all phases from a conceptualand environmental protection. Design and application to realprojects were conducted by recent studies (Brown et al., 2004;Choi, 2006; Choi and Do, 2006; Choi et al., 2008; Choi et al., 2010).development to abandonment. Systematic review of risksshall be carried out at all phases to identify and evaluatethreats, consequences of a single failure and series of failuresThis paper is presented to summarize the recent designcode and to establish a wall thickness design matrix. Themain objective of this paper is to assess a parametric study ofin the pipeline system. A methodology for a systematicreview is quantitative risk analysis (QRA). There are twoCorrdsponding author Han-Suk Choi: 77 Cheongam-Ro, Nam-Gu, Phohang, Korea, 82-54-279-0134, hchoi@postech.ac.kr본 연구는 2011년 부산, BEXCO 에서 개최된 한국해양과학기술협의회 공동학술대회에 발표된 논문을 근간으로 하고 있음을 밝힙니다.1
2Han-Suk Choi, Su-Young Yu, Dae-Hoon Kang and Hyo-Dong Kangparts of safety philosophy such as safety class methodologyand quality assurance. Structural safety of the pipeline systemis ensured by use of a safety class methodology based onfailure consequences and a set of partial safety factors.Quality objectives are established by the operator of pipelinesystem and a quality assurance is controlled during allrelevant phases.Generally, pipeline system design is conducted in compliance with national legislation and company policy withrespect to health, safety and environmental aspects as well asdesignated design codes such as DNV-OS-F101.The objective of concept development and design premiseprovide a basis for the definition of relevant offshore field development characteristics. When selecting a pipeline systemconcept in a stage of development, all aspects related todesign, construction, operation and abandonment shall be considered. Data and description of a field development andgeneral arrangements of the pipeline systems are established.The pipeline system shall be designed, constructed andoperated in such a manner that the specified transportcapacity is fulfilled and the flow assured. Resistance againstloads and the safety margin against accidental loads or unplanned operational conditions shall be fulfilled. A designmatrix was established to satisfy the concept development anddesign premise. Parameters which could affect on theintegrity of a pipeline system were evaluated in this study.compressive forces (load controlled) shall be also considered. (1) where , local incidental pressure during operation , local system test pressure during system test external pressure material resistance factor safety class resistance factor characteristic wall thickness , pressure containment resistance where pipeline wall thickness nominal outside diameter where yield stress tensile stress3.2 Local buckling - external over-pressure only (systemcollapse)The characteristic resistance for external pressure is calculated as: 3. Design - Limit State Criteria (2)All relevant limit states shall be considered in a design forall relevant phases and conditions. As a minimum requirement of an ultimate limit state, the offshore pipeline systemshall be designed against bursting, ovalization/ratcheting,local buckling, global buckling, fatigue, unstable fracture andplastic collapse. The design matrix is based upon several limitstates and partial safety factors, is also called as a load andresistance factor design.The design load should be checked by the limit state designcriteria. These criteria include load scenarios to be considered,categorization of loads such as functional, environmental andaccidental loads. All loads and forced displacements whichinfluence the pipeline integrity were considered in this study.where characteristic resistance for external pressure(collapse) , elastic collapse pressure , plastic collapse pressure m ax m i n , ovality where fabrication factor m ax greatest measured inside or outside diameter m i n smallest measured inside or outside diameter3.1 Pressure containment (bursting)A bursting of pipeline due to the fluid pressure containment shall be satisfied the following criteria. The criteria arevalid if the pipe mill pressure test has been satisfied. If not, acorresponding decreased utilization factor shall be applied.Reduction in pressure containment resistance due to true3.3 Propagation bucklingPropagation buckling cannot be initiated unless a localbuckling has occurred. Propagation buckling results in verythick pipes. Propagation buckling is an option for the wallthickness design. If the external pressure exceeds the propa-
Parametric Study of Offshore Pipeline Wall Thickness by DNV-OS-F101, 2010gation criteria, buckle arrestors should be installed. A bucklearrestor capacity depends on propagating buckle resistance ofadjacent pipes and size of the buckle arrestor (Torseletti et al,2003). The propagating buckle criterion is as below: (3) 3force and external over-pressure are deigned to satisfy thefollowing condition: m i n , where (5)wherefor ,propagatingpressurewhere m i n minimum internal pressure3.4.2 Displacement controlled conditionDisplacement controlled condition is that the structuralresponse is primarily governed by imposed geometric displacements. characteristic wall thickness3.4 Local buckling - combined loading criteria3.4.1 Load controlled condition (LCC)Load controlled condition is that the structural response isprimarily governed by the imposed load. This designcriterion can always be applied in place of a displacementcontrolled condition (DCC) (DNV, 2010).(1) Internal over-pressurePipe members subjected to bending moment, effective axialforce and internal over-pressure are deigned to satisfy thefollowing condition: (bending moment and axial force) and internal over-pressureare designed to satisfy the following condition: m i n (6)where design compressive strain m i n m i n (1) Internal over-pressurePipe members subjected to longitudinal compressive strain strain resistance factor , (4) girth weld factor m ax , minimum strain hardeningwhere design momentwhere strength equivalent to a total elongation of 0.5 % design effective axial force internal pressure(actual stress) , plastic capacity of effective axial tensile strengthforce , plastic capacity of design moment , flow stress parameter wing condition: , effect of ratio forfor for(2) External over-pressurePipe members subjected to longitudinal compressive strainand external over-pressure are designed to satisfy the follo-,factorusedin m i n m i n (7)4. Design Matrixcombined loading criteria(2) External over-pressurePipe members subjected to bending moment, effective axial4.1 Input parametersInput parameters used in a benchmark case are shown inTable 1. These data were taken from the Sakhalin 1, Chayvo-
4Han-Suk Choi, Su-Young Yu, Dae-Hoon Kang and Hyo-Dong KangTable 1 Input parameters for wall thickness calculation (Benchmark case)InputValueOutside diameter914.4 mmCorrosion allowance3 mmWater depth21.8 mBurial depth2.35 mDesign pressure9.763 MPaOperating temperature68 Effective axial force222.4 kNMoment1897 kNㆍmStrain0.002Specified minimum yield stress415 MPaSpecified minimum tensile stress520 MPaElastic modulus207 GPaPoisson ratio0.3Orlan pipeline project (Technip, 2005).loped under a consistent design methodology and philosophyfor wall thickness design. Then, this design matrix was usedfor a benchmark case and a parametric study. The designmatrix for the benchmark case of wall thickness is internalover-pressure problem as shown in Table 2. The benchmarkcase shows the negligible results for external over-pressurecases. External over-pressure and other parametric studies arepresented in the following section.5. Parametric Sensitivity AnalysesParameters and the varied values used in sensitivityanalyses are indicated in Table 3. After numerous calculations,appropriate ranges of variables were determined to identifytheir sensitivities.Fig. 1 shows a parametric analysis of water depths for internalover-pressure cases. Propagation buckling is the most sensitive to the water depth. Displacement controlled combined4.2 Design matrixload cases are also sensitive to water depth due to minimuminternal pressure that can be continuously sustained with theassociated strain. However, load controlled combined condi-A design matrix was developed to include the designfactors of pipeline integrity, public safety, and environmentalprotection in DNV-OS-F101. This design matrix was deve-tions indicate tendency of decrement of wall thickness due tomaximum internal pressure. Water depth increments have alsonegative effects for pressure containment cases.Table 2 Design matrix for wall thickness calculations (Benchmark case)CasePressure containment (bursting)DescriptionSystem conditionWall thickness gh19.8Code sectionD200System testLow14.5Local buckling - Externalover-pressure (system collapse)Installation & operationHigh13.6D400Propagation bucklingInstallation & operationHigh19.4D500Internal over-pressure(System check)Local buckling - Combinedloading criteria(load controlled condition)External over-pressure(System check)Internal over-pressure(Local check)External over-pressure(Local check)Internal over-pressure(System check)Local buckling - Combinedloading criteria(displacement controlledcondition)External over-pressure(System check)Internal over-pressure(Local check)External over-pressure(Local .818.9HighD60920.1
Parametric Study of Offshore Pipeline Wall Thickness by DNV-OS-F101, 2010Table 3 Parameters for sensitivity analysesParametersValuesWater depth(Internal over-pressure)0 950 mWater depth(External over-pressure)100 1,000 mBurial depth0 5 mAxial force- 5,000 5,000 kNMoment- 5,000 5,000 NㆍmStrain0 0.01Temperature50 200 5sensitive to the wall thickness design. Both of the combinedload cases are also sensitive to wall thickness. Results ofpressure containment does not appear in this figure due toexternal over-pressure cases.Fig. 3 illustrates a parametric analysis of pipeline burialdepths. The results of parametric study are separated into twogroups. Upper group including pressure containment inoperation, propagation buckling and displacement controlledcondition is more sensitive than lower group. Most of theresults show mild rates of increments with respect to pipelineburial depths.Fig. 4 shows a parametric analysis of effective axial forces.Effective axial forces have influence only on load controlledcombined conditions. Wall Thickness is very sensitive to axialforce increment. Increments of wall thicknesses by compressive and tensile force are symmetric.Fig. 1 Wall thickness results of water depths for internal overpressure cases (Pi 9763 kPa)Fig. 2 indicates a parametric analysis of water depths forexternal over-pressure cases. Propagation buckling is the mostFig. 2 Wall thickness results of water depths for external overpressure cases (Pi 976 kPa)Fig. 3 Wall thickness results of burial depthsFig. 4 Wall thickness results of effective axial forces
6Han-Suk Choi, Su-Young Yu, Dae-Hoon Kang and Hyo-Dong KangFig. 5 illustrates a parametric analysis of moments on pipeline systems. Moment has a significant influence only on loadcontrolled combined conditions for wall thickness design.There are little differences in wall thicknesses between systemcheck cases and local check cases due to the load controlcondition by external moments.Fig. 6 shows a parametric analysis of strains due to pipeline installation. System check cases in displacement controlled condition are more sensitive than load controlled condition. As strains are increased, the wall thickness in systemcheck case is increased linearly within allowable strain limits.Fig. 7 shows a parametric analysis of operational temperatures. Pressure containment in the high safety case and operation case are the most sensitive to the operational temperatures. Displacement controlled condition and propagation buckFig. 7 Wall thickness results of operating temperaturesling cases are also sensitive to the operational temperatures.But load controlled condition cases show mild increments ofwall thicknesses.Fig. 8 shows a summary of the parametric sensitivity analyses. Vertical axis indicates the ratios of wall thicknesses between the benchmark case and sensitivity analyses. Horizontalaxis indicates the ratios of the parameters between thebenchmark case and sensitivity analyses. Load controlledcases due to external moments and installation strains aremost sensitive to wall thickness design. Water depth is alsosensitive to wall thickness, but less sensitive than combinedload cases. Remaining parameters such as burial depth, axialforce, and operating temperature have little influences forFig. 5 Wall thickness results of external momentswall thickness design. These tendency is similar to the resultsof Vitali et al (1999).Fig. 6 Wall thickness results of pipeline strainsFig. 8 A summary of the parametric sensitivity analyses
Parametric Study of Offshore Pipeline Wall Thickness by DNV-OS-F101, 20106. Concluding Remarks7Following concluding remarks were obtained from theChoi, H.S. (2006). “A Benchmark Study of Design Codes onOffshore Pipeline Collapse for Ultra-Deepwater”, The Society of Naval Architects of Korea, SOTECH, Vol 10, No 1,parametric sensitivity study.(1) A design matrix was developed in accordance with DNVOS-F101, 2010. Then the design matrix was used for a realpp 38-46.Choi, H.S. and Do, C.H. (2006). “Integrated Expansion Analysis of Pipe-In-Pipe Systems”, Journal of Ocean Enginee-project benchmarking and parametric sensitivity analyses.(2) In case of water depth variations, propagation bucklingis the most sensitive to the wall thickness design.ring and Technology, The Korean Society of Ocean Engineers, Vol 20, No 5, pp 9-14.Choi, H.S., Lee, S.K. and Chun, E.J. (2008). “A Review of(3) Results of pipeline burial depth variation are separatedinto two groups. The group including pressure containmentin operation, propagation buckling and displacement controlledExpansion Behavior of Marine Pipelines”, Journal of OceanEngineering and Technology, The Korean Society ofOcean Engineers, Vol 22, No 2, pp 13-19.condition is sensitive to wall thickness design.(4) Effective axial forces and moments have influenced onlyload controlled conditions. The results of system check casesChoi, H.S., Do, C.H. and Na, Y.J. (2010). “Expansion Spool Design of an Offshore Pipeline by the Slope Deflection Method”, Journal of Ocean Engineering and Technology, Theare higher than those of local check cases.(5) System check cases in displacement controlled conditions are more sensitive than those of load controlled condi-Korean Society of Ocean Engineers, Vol 24, No 5, pp 1-7.DNV (1976). Rules for the Design, Construction and Inspection of Submarine Pipelines and Pipeline Risers, Det Nor-tions.(6) Results of operational temperature variation show thatpressure containment, displacement controlled condition andske Veritas., Hovik.DNV (1981). Rules for the Submarine Pipeline Systems, DetNorske Veritas., Hovik.propagation buckling cases are sensitive to the wall thicknessdesign.(7) External moments and installation strains are the mostDNV (2000, 2005, 2007, 2010). Submarine Pipeline Systems, Offshore Standard DNV-OD-F101, Det Norske Veritas., Hovik.Technip (2005). Mechanical Design of Chayvo-Orlan Pipelines,sensitive to wall thickness design. Water depth is an important variable to design wall thickness, but less sensitive thanthe combined load cases.NCS Sakhalin 1 EPC 2 - Offshore Pipeline, Doc. No.RUSA-RJE-GL-YR-61600.8115, Technip, Houston.Torseletti, E., Bruschi, R., Marchesani, F. and Vitali, L. (2003).후기본 연구는 대우조선해양(주)의 지원으로 수행된 연구결과 입니다.참 고 문 헌“Buckle Propagation and its Arrest: Buckle Arrestor Design Versus Numerical Analyses and Experiments”, Vol 2,OMAE 2003-37220, pp 661-674.Vitali, L., Bruschi, R., Mørk, K. and Verley, R. (1999).“Hotpipe project - Capacity of Pipes Subjected to InternalPressure, Axial Force and Bending Moment”, Proc. 9th Int.Offshore and Polar Engineering Conference, Brest.Brown, G., Tkaczyk, T. and Howard, B. (2004). “ReliabilityBased Assessment of Minimum Reelable Wall Thickness2011년 8월 22일 원고 접수for Reeling”, Proceeding of IPC 04-0733, IPC Calgary,Alberta, Canada.2012년 4월 19일 게재 확정2012년 1월 3일 심사 완료
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