Weight Optimized SCR: Enabling Technology for Turret Moored FPSO Developments

Foyt, Elizabeth; Griffin, Cary; Campbell, Mike; Wang, H. Howard; Kan, Wan C.

doi:10.1115/omae2007-29049

Cited by 8 publications

(5 citation statements)

References 1 publication

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“…Previous study shows the magnitude of compression is highly correlated with axial downward heave velocity at porch location, [4]. Vessel motion time series which is equivalent to the condition of 100-yr hurricane of GOM (JONSWAP, Hsϭ14.8m, Tpϭ14.7s, ␥ϭ2.6) is applied, and the mean vessel offset is assumed to be 5% of water depth.…”

Section: Analysis Methodologymentioning

confidence: 99%

Dynamic Plastic Deformation of Deepwater Steel Catenary Risers under Extreme Cyclic Compressive Loading

Hu¹,

Campbell²,

Huang³

2014

Day 1 Mon, May 05, 2014

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Steel catenary risers (SCR) on a large heave motion vessel are susceptible to compression in the riser touch down zone (TDZ). Dynamic compression can lead to over stress under extreme or abnormal weather conditions. The response of an SCR under compression is highly nonlinear and sensitive to various factors. However, the current available industry design codes and practices do not provide a clear guidance to address the acceptability of compression, over stress and the resulting plastic strains. In addition, the current analysis method used in industry common practice cannot accurately capture the nonlinear behavior of SCR involving accumulated plastic deformation, hysteresis effects and local buckling.In this paper, a finite element analysis (FEA) modeling method using combined beam and solid elements is presented that enables simulation of large plastic deformation, pipe ovality and local pipe buckling in the TDZ of a deepwater SCR. The model is developed using ABAQUS. The SCR nonlinear response is examined through dynamic analysis of a deepwater SCR hung-off a semi-submersible. The key analysis results are compared with a nonlinear beam element model. Moreover, dynamic ratcheting analysis under multiple plastic strain cycles using the proposed solid riser model is conducted to understand the plastic strain accumulation and to check the acceptability of survival response of deepwater SCR under a series of severe Hurricanes in its service life.This paper presents the methodology of evaluating the compression and plastic deformation that could be experienced by deepwater SCRs, including modeling approach, analysis results, possible failure modes, and conclusions. The impact of the study findings on the robustness and suitability of SCRs for deepwater application are discussed.

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Section: Analysis Methodologymentioning

confidence: 99%

Dynamic Plastic Deformation of Deepwater Steel Catenary Risers under Extreme Cyclic Compressive Loading

Hu¹,

Campbell²,

Huang³

2014

Day 1 Mon, May 05, 2014

Self Cite

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“…These design challenges can be successfully addressed by introducing a SCR concept with varying weight along the riser and with the lightest possible cross-sections in the Touch Down Zone (TDZ), Karunakaran et al (2002), Karunakaran et al (2005) and Foyt et al (2007). However, design of SCRs for harsh environment has been a great challenge, especially from large motion host platforms such as semi-submersible platforms.…”

Section: Introductionmentioning

confidence: 99%

Fatigue Enhancement of SCRs: Design Applying Weight Distribution and Optimized Fabrication

2013

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Steel catenary risers (SCR) have been an attractive choice for recent deep-water field developments. However, design of SCRs for harsh environment or from large motion host platforms has been a great challenge. The key issues for the design of SCRs in harsh environment are the fatigue near the hang-off and at the touch down point.Design of SCRs by distributing weight along the riser enhances the fatigue performance of SCRs thereby extending the feasibility of SCRs for deep water harsh environment whilst fulfilling both strength and fatigue requirements. The weight distribution along the SCR is obtained by fully qualified ballast modules and also fully qualified light weight add-ons at TDP which are designed for mud-line application. Further, by high quality welding and optimized weld geometry, the fatigue performance of the SCR welds are improved and optimized. This paper also describes the mechanism that drives the weight distributed SCR design and also fatigue test data from optimized weld geometry.The results clearly indicate that it is possible to have a robust design of SCRs from large motion host platforms in harsh environments using presently qualified materials and technology. These qualified products extend the applicability of the weight distributed SCR concept to most dimensions and applications. This concept is also applicable in less demanding environments. Based on the work, the applicability of this concept is mapped out for various floater motions.Fatigue test results are presented from both carbon steel and clad/lined riser qualification programs which will demonstrate that high fatigue performance can be sustained with established girth welding procedures with appropriate control of pipe fit up tolerances and weld soundness.The weight distributed SCR concept, combined with high performance welds, will make the applicability of SCRs a credible alternative option for use in increasingly harsh environments or from host platforms with large motions. Since the ballast and light weight add-ons are fully qualified material they are cost effective and ready for project application.

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“…The SCR with weighted sections, which improve SCR response at critical area, is a potential alternative solution for the application of SCRs in deep water and harsh environment (Foyt et al, 2007). According to , the distribution weight can be achieved by using well qualified ballast modules that are attached at certain sections of SCR.…”

Section: Weight Distributed Scrmentioning

confidence: 99%

Feasibility Study of Selected Riser Concepts in Deep Water and Harsh Environment

Gemilang

Karunakaran

2017

Volume 5B: Pipelines, Risers, and Subsea Systems

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Todays, oil and gas sources are explored in deep water and harsh environment. A riser system is one of the major sub-facilities to transfer oil and gas from the seabed to the host platform. One of the well-known riser systems, the Steel Catenary Riser (SCR), has been an attractive choice for the riser system in deep water. However, the main challenge of the SCR is large motions from the host platforms due to the harsh environment. The large motion of host platforms may induce excessive buckling and fatigue at the touchdown point. The key component of the large motion of the host platform is the downward velocity at the hang-off point where the top-end of the riser is attached to the host platform.By screening the downward velocities at the hang-off point in the time history graph, the time at which the critical responses (i.e. buckling utilization, bending moment and compression) peak is identified. This study investigates the feasibility of the SCR configuration in terms of the capability to cope with the vessel motion. Several types of the SCR configurations are proposed in this study. The selected configurations of SCR in this study are conventional SCR, Weight Distributed SCR (WDSCR), and Steel Lazy Wave Riser (SLWR). The feasibility of the three riser configurations was analyzed in terms of strength and fatigue performance to understand the limitation of one over the other. The strength assessment of the risers was performed by using load cases, the screening approach was based on different extreme downward velocities at the hang-off point. The checks were according to DNV.The fatigue performance of the risers was checked considering both wave-induced fatigue and fatigue due to vortex induced vibration. Overall, from the extreme response analysis study, results showed that a feasible conventional SCR configuration can be obtained if the downward velocity at the hang-off point is restricted below 2.6 m/s. It is also found that the downward velocity at the sag-bend of the conventional SCR is restricted below 3.03 m/s. On the other hand, a feasible WDSCR configuration can be obtained, if the downward velocity at the hang-off point is restricted below 3.2 m/s. It is also found that the downward velocity at the sag-bend of the WDSCR is restricted below 3.43 m/s.The heavy cross section of WDSCR reduces the critical responses (i.e. bending moment, compression and utilization) at the TDP and extends the feasibility of the SCR. The results showed that the SLWR configuration can cope even with a downward velocity of 6 m/s at the hang-off point. The "lazy wave" configuration efficiently absorbs the vessel heave motions. Thereby the SLWR configuration is proven to be the most robust configuration to cope with large motion of the host platform. This study proves that although the SCR feasibility is limited due to vessel heave motion, innovative solutions can be established to extend its feasibility in order to cope with the vessel heave motion in harsh environment.

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Weight Optimized SCR: Enabling Technology for Turret Moored FPSO Developments

Cited by 8 publications

References 1 publication

Dynamic Plastic Deformation of Deepwater Steel Catenary Risers under Extreme Cyclic Compressive Loading

Dynamic Plastic Deformation of Deepwater Steel Catenary Risers under Extreme Cyclic Compressive Loading

Fatigue Enhancement of SCRs: Design Applying Weight Distribution and Optimized Fabrication

Feasibility Study of Selected Riser Concepts in Deep Water and Harsh Environment

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