Elsevier

Ocean Engineering

Volume 84, 1 July 2014, Pages 273-282
Ocean Engineering

An efficient design methodology for subsea manifold piping systems based on parametric studies

https://doi.org/10.1016/j.oceaneng.2014.03.021Get rights and content

Highlights

  • Proposed an efficient design procedure for subsea manifold piping systems.

  • Provided of a detailed numerical analysis (FEM and FVM) based parametric study.

  • Recommendations for the design of optimal subsea manifold piping systems.

Abstract

Subsea manifolds are widely used in the development of oil and gas fields to simplify the subsea system, minimise the number of subsea pipelines/risers and optimise the flow path in a piping system. The piping system is designed to satisfy the requirements for internal pressure, thermal loads, hydrostatic collapse and external operational loads under extreme environmental conditions. At present, however, there are no efficient and well-defined design procedures available that accurately predict the effects of extreme environmental conditions on pressure drop, total deformation, weight and erosion characteristics given varying design parameters considered throughout the piping system. Therefore, it is necessary to develop an new design procedure for subsea manifold piping systems with complicated shapes capable of sustaining erosion inside the piping system. The aim of this study is to develop a design procedure for subsea manifold piping systems based on a variety of parameters of influence under extreme environmental conditions, including high pressure and high temperature. A detailed numerical analysis of nonlinear finite element method and finite volume method is conducted to develop the proposed design procedure based on the results of parametric studies and generates some recommendations for the design of optimal subsea manifold piping configuration systems. The design procedure presented here will assist the design and analysis of subsea manifold piping systems.

Introduction

The global demand for energy continues to increase, and onshore and shallow water energy sources are becoming significantly depleted. As the world׳s economies and populations grow, oil and gas prices are expected to continue to rise. This prediction of oil prices improves the economic feasibility of offshore deep-water oil field development, although the environmental features are extreme. Lu et al. (2011) noted that the environmental features of deep water reservoir (9153000 m) are extreme conditions such as high pressure (HP: 69–207 MPa) and high temperature (HT: 149177 °C), and claimed that the development of enduring HP and HT technologies is essential to the efficient operation of subsea systems in deep water. Therefore, high pressure and high temperature related subsea engineering technologies are becoming increasingly attractive as the oil and gas industries continue to explore and exploit deeper waters.

Recognising the importance of offshore deep-water oil fields, oil producing countries and industries have pushed the development of subsea technologies, especially subsea manifolds that simplify subsea systems, minimise the number of pipelines/risers and optimise the flow path in subsea systems. This explains why the role of subsea manifolds has become increasingly important in deep-water field development to save costs.

In oil and gas industries, components of subsea manifold piping system including, straight piping, header, and branch piping should be designed based on DNV OS-F101 (DNV OS-F101, 2010) or ASME B31.4 (ASME B31.4, 2009). According to them, a thickness of the entire piping should be designed to satisfy the requirements for internal pressure, thermal loads, hydrostatic collapse, and external operational loads. Further, when designing piping components, there are a lot of analysis issues to be considered including internal pressure, hydro-testing, thermal loads, operating with jumper loads, flowline jumper connection loads, well jumper connection loads, environmental loads, external corrosion, internal corrosion/erosion and piping supports to accommodate all anticipated loading, deflections, and vibrations. Current design methodologies are sequential design procedure which moves to next design step when satisfying each requirement. The strength of sequential design procedure is that it is able to achieve systematic and reliable design, while it has the weakness that it is unable to consider the interactions among design parameters. Furthermore, when the initial design changes, it is highlighted that all requirements must be reviewed from scratch. In this aspect, it is noticed that development of a design procedure considering the interaction of design parameters is very important from the point of view of reducing design costs under deep-water environmental features.

Looking into the details of subsea piping configuration recommended by the rules ISO 13628-15 (ISO 13628-15, 2011), the minimum length of straight pipe should be 7 times the inner diameter (DI) of piping and the location of bends should allow straight runs of at least 3D before and after. According to ASME B16.28 (1994), the bend radius should be the same as nominal pipe size (NPS). It is however found that the design criteria for piping components are available but the design procedure of piping configuration is not proposed yet. This is meant by that the piping configuration, arrangements of manifold piping components and use of flanged or welded components are basically dependent on the designer. Thus, in industries, the piping configuration is dependent on manufacturers׳ criteria, because only functional requirements are typically established by the operators. In the current design environment, total weight of subsea manifolds is only dependent on designer׳s choice although it is one of the primary issues for installation. In the installation of subsea equipment, light design proposal is more beneficial. In this aspect, it is better to consider an optimisation of piping configuration in an early design stage in order to reduce total weight of subsea manifolds.

It has been also recognised that pressure drop in pipes is an important consideration when designing a variety of industrial fluid flow equipment. A single-phase pressure drop in pipe flow is not only the basis for determining the single-phase friction pressure drop, but also the foundation of pressure drop calculations for multiphase flow. The design technologies associated with pressure drop in two-phase flow have proven to be an important issue for the oil and gas industries. The study of pressure drop in pipe flow (Nikuradse, 1933, Colebrook, 1938, Moody, 1944, Dang and Hihara, 2004, Huai et al., 2005, Incropera and DeWitt, 2001, Son and Park, 2006, Yoon et al., 2003) has been documented widely in the literature and the basic hydrodynamic characteristics are fairly well understood for simple pipelines. However, previous studies are focused on developing equations of friction factors for simple and large structures based on the physical phenomena, which are insufficient for designing subsea manifold piping systems relatively small and complicated shapes. Therefore, a design procedure for subsea manifold piping systems considering the interaction of parameters on pressure drop is needed.

In the oil and gas industries, design technologies related to the flow of fluids usually contain hard particulate matter that can cause equipment degradation through surface material erosion. This aspect will be more pronounced in the deep-water environment, because subsea structures are typically subjected to extreme actions arising from service requirements. The maintenance of eroded subsea structures is very costly, and thus the procedure of damage-tolerant designs and condition assessments of subsea structures are desirable for academic purposes even though current design methodologies overestimate erosion effects to avoid the erosional issues. For this purpose, we must better understand how operational and environmental conditions affect pressure drop, maximum and mean erosion rate densities. Several studies have addressed this topic in the literature (Venkatesh, 1986, Huser and Kvernvold, 1998, Salama and Venkatesh, 1983, Svedeman and Arnold, 1993, Salama, 1998, Bourgoyne, 1989, McLaury et al., 1997, Barton, 2003), but it is still necessary to develop the design procedure for subsea manifold piping systems with complicated shapes capable of sustaining erosion inside the piping system.

The aim of this study is to propose the design procedure based on the numerical results of nonlinear structural response and flow characteristics with varying design parameters for subsea manifold piping. Although there are a lot of aspects to be taken into account when designing subsea manifold piping systems, the present study is concerned with parametric studies of pressure drop, total deformation and erosional characteristics. The proposed design procedure is constructed in two phases, Step 1 and Step 2. In each step, a sensitivity analysis is carried out based on the results of parametric studies. In order to validate the proposed design procedure, an applied example is performed for the four-slot cluster manifold shown in Fig. 1. The design conditions of the present study is shown in Table 1 and thus the optimisation will be carried out.

The strength of numerical methods includes enhanced design, better insight into critical design parameters, virtual prototyping, a faster and less expensive design cycle and increased productivity compared to experiments. On the other hand, it is well known that the speed of a numerical simulation is slow for large structure with fine mesh and if simple numerical assumptions are applied for numerical method calculations, false results might be obtained. Therefore, when applying numerical methods, mesh convergence study and the precise setting of simulations are required to be carried out by all means.

In the present study, the proposed design procedure is developed based on a numerical results of the finite volume method (FVM) and the nonlinear finite element method (NLFEM). The finite volume method simulation deals with pressure drop and erosional characteristics of the manifold piping system in single-phase steady-state flow. The nonlinear finite element method adopts a one-way fluid structure interaction (FSI) method. The calculated pressure and temperature distribution of fluid model are directly mapped along the inner surfaces of the structure model in order to calculate total deformation of subsea manifold piping systems.

In the optimisation study, central composite design (CCD), the response surface method and screening method are applied. Authors recommend that the proposed deign procedure is to be performed for a project base because the environmental and operational conditions vary depending on a field reservoir. In the present study, because limited numbers of parameters are applied, the results of the applied example only cover within proposed scope of design parameters and can be significantly improved when applying more parameters.

ANSYS Workbench (Version 14.0) is used for the present study; specifically, CFX for the flow analysis, Static Thermal and Static Structure for the thermal-structural analysis, Design-Xplorer for the optimisation and Inventor for the geometry modelling.

Section snippets

Proposed design procedure

This section summarises the proposed two-step design procedure for subsea manifold piping systems (Steps 1 and 2), as depicted in Fig. 2.

The objective of Step 1, called general design phase, is to identify parameter variation effects on flow characteristics and structural responses among candidate models and to select the best model in terms of minimum values of pressure drop, total deformation and weight based on the results of parametric studies. The flow velocity, fluid temperature and the

Applied example

A series of finite volume method and nonlinear finite element method analyses are now undertaken as an applied example to validate the proposed design procedure.

Conclusions

The aim of this study is to develop the efficient design procedure for subsea manifold piping systems under high pressure and high temperature. For this purpose, a series of the finite volume method and nonlinear finite element method computations are undertaken on subsea manifold piping models by the proposed design procedure.

Based on the results obtained from the present study, the following conclusions can be drawn.

  • (1)

    It is confirmed that the finite volume method and the nonlinear finite

Acknowledgements

This research was supported by Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Ministry of Science, Ict & future Planning(MSIP) (Grant no.: 2013044761). The study was undertaken at the Lloyd׳s Register Foundation (LRF) Research Centre of Excellence (Ship and Offshore Research Institute) at Pusan National University, South Korea. Some part of this study was presented in the 12th International Symposium on

References (23)

  • DNV OS-F101, 2010. Submarine Pipeline Systems. Det Norsk...
  • Cited by (0)

    View full text