Segen F. Estefen

Strength Analyses of Sandwich Pipes for Ultra Deepwaters

Design requirements for pipelines regarding both ultimate strength and flow assurance in ultra deepwater scenarios motivated the development of a new sandwich pipe which is able to combine high structural and thermal insulation properties. In this concept, the annulus is filled with low cost materials with adequate thermal insulation properties and good mechanical resistance. The aim of this research work is to perform small-scale laboratorial tests and to develop a finite element model to evaluate the structural performance of such sandwich pipes with two different options of core material. After calibrated in view of the experimental results, a three-dimensional finite element model incorporating nonlinear geometric and material behavior is employed to perform strength analyses of sandwich pipes under combined external pressure and longitudinal bending. Ultimate strength envelopes for sandwich pipes are compared with those generated for single-wall steel pipes with equivalent collapse pressures. The study shows that sandwich pipe systems with either cement or polypropylene cores are feasible options for ultra deepwater applications.

Wave-to-Wire Model and Energy Storage Analysis of an Ocean Wave Energy Hyperbaric Converter

This paper addresses the dynamic modeling and the energy storage analysis of a wave energy hyperbaric converter, which consists of a set of oscillating bodies (named as pumping modules) linked to hydropneumatic accumulators and an electric generating unit. A mathematical model of the accumulator is presented and a model for the generating unit is proposed, including a nonlinear model of a Pelton turbine. Then, the hydrodynamic, mechanical, and electrical characteristics of the subsystems that compose the converter are discussed. With the proposed model, it is possible to evaluate the dynamic behavior of the entire system. That is, for a given incident ocean wave, it is possible to evaluate all the system state variables and the generated electric power, including the quality (fluctuation, for example) of the generated voltage and frequency for islanded or power-grid-connected operation. Simulation results considering the proposed wave-to-wire model under the action of regular and irregular incident waves are presented to illustrate the performance of the system.

Buckle arrestors for deepwater pipelines

Two different buckle arrestor configurations were tested experimentally in order to evaluate the feasibility of using them for deepwater pipelines. Long steel alloy pipes with diameter-to-thickness ratios of 16 and 23 were provided with buckle arrestors and tested under quasi-static conditions in a hyperbaric chamber. Empirical formulae were obtained from the experimental results taking into account both pipe and buckle arrestor geometries as well as material properties.

DESIGN ASPECTS AND BENEFITS OF SANDWICH PIPES FOR ULTRA DEEPWATERS

Oil&gas production on deep and ultra deepwater scenarios require very thick walled steel pipelines or heavy Pipe-in-Pipe systems, which are expensive and difficult to install. Sandwich Pipe is a new pipeline concept composed of two concentric steel pipes separated by and bonded to a polymeric annulus that provide the adequate combination of structural strength and thermal insulation. In later works, Sandwich Pipes have been analyzed regarding to the structural strength and results have indicated good relation between steel weight and external pressure resistance, mainly when compared to the Pipe-in-Pipe system. To fulfill the thermal insulation requirements, an adequate polymer for the annular layer should be selected, combining both insulation requirements and good bonding strength to steel, which are determinant for the adequate performance. Sandwich Pipes with typical inner diameters of those employed in the offshore production are analyzed numerically to evaluate the ultimate strength under external pressure. Polyurethane based materials with different mechanical and thermal properties are selected. Experimental tests are performed to evaluate adhesion strength to steel, which are used as input for the numerical models. Non-linear geometry, material and contact properties are included, as well as temperature effect on polymer stiffness. To estimate the insulation capacity for each option the global heat transfer coefficient is calculated and a maximum “U value” is considered for all systems. Also, both numerical and analytical analyses are employed to design a PIP system for a hypothetical offshore field. Similar conditions to the newly discovered sub-salt fields offshore Brazil are adopted, i.e. 2500 m water depth and 80°C produced fluid temperature. API 5L specifications table are used for thickness and diameter selection and API RP1111 is employed to design PIP inner pipe. Results indicate that Sandwich Pipes with adequate strength and insulating annular material can generate significant advantages in relation to the PIP system. In addition to the sandwich structure benefit, the initial out-of-roundness maximum diameter directions between inner and outer pipes have a secondary role that produces additional strength for the collapse pressure resistance. Lower steel weight is calculated in all cases, even when the outer pipe is larger. All cases yielded lower submerged weight, which is an important parameter for installation purposes, because less expensive lay vessels may be required.Copyright

Parameter determination of double-ellipsoidal heat source model and its application in the multi-pass welding process

The parameters of the heat source model have significant influence on the temperature field and sequentially affect the residual stress field. In this paper, a neural-network programme based on the Levenberg–Marquardt algorithm is developed to predict the parameters of Goldaks double-ellipsoidal heat source model. The analytical solution of the heat conduction equation based on the double-ellipsoidal heat source is obtained by integrating a series of instant point heat sources over the volume of the ellipsoidal heat source. The transient temperature distribution and the sizes of the molten pool are obtained under various welding processes by using the analytical method. Then, a neural-network programme is employed to train and predict the heat source parameters. These results of temperature and molten pool size obtained by the numerical simulation with the predicted heat source parameters are calibrated by the published experimental results. The numerical results show a good agreement with the experimental measurements. Finally, the developed Levenberg–Marquardt neural network is employed to predict the heat source parameters in the multi-pass welding process in the laboratory. By comparing the finite element (FE) numerical results with experimental results, the heat source parameters have been successfully identified in the multi-pass welding process.

Efficiency optimization in a wave energy hyperbaric converter

This paper considers the problem of optimizing the efficiency of the primary conversion on an ocean wave energy hyperbaric converter. This wave energy converter (WEC) is an oscillating-body linked to a hyperbaric chamber. By solving the equation of motion of the power take-off mechanism, it is shown that optimal conditions for improving the absorbed power relate the buoy parameters and the chamber pressure with the incident waves. This work also proposes an algorithm for finding the best time interval that the body remains locked when latching control strategy is used to enhance the efficiency of the WEC. Numerical simulations are presented in order to evaluate the optimum conditions of the hyperbaric WEC and the performance of the proposed algorithm.

ADHESION EFFECT ON THE ULTIMATE STRENGTH OF SANDWICH PIPES

Sandwich pipes composed of two steel layers separated by a polypropylene annular can be used for deepwater oil&gas transportation. They combine high structural strength to resist external pressure with thermal insulation to prevent blockage by paraffin and hydrate. In this work, experimental tests and numerical models were employed to verify the influence of the inter-layer adhesion on the ultimate strength under external pressure and longitudinal bending of a sandwich pipe prototype. The maximum shear stress obtained from sandwich pipe specimens bonded with a specific adhesive indicated the adhesion levels to be adopted in the numerical simulations. Two contact models were employed to simulate the bonding and slipping conditions between layers, one adopting a friction model and the other including non-linear springs between metal and polymer nodes. The latter is an adapted solution to simulate both tension and shear loads. As expected for a sandwich structure, the structural strength is strongly dependent on the interface stickiness. The analyzed geometry is able to withstand a water depth up to 3,000 meters with a bonding strength corresponding to only 10% of the idealized perfect adhesion condition.Copyright

Wave Climate Analysis for a Wave Energy Conversion Application in Brazil

A variety of ocean wave energy conversion devices have been proposed worldwide considering different technology and energy extraction methods. In order to support full-scale prototype design and performance assessments of a conversion scheme to be deployed on the northern coast of Brazil, a long-term wave climate analysis is under development. A 5-year pitch-roll buoy data series has been investigated through an adaptive technique to enhance spatial resolution and allow for accurate wave directionality evaluation. Device design most influential variables such as extreme significant wave height, peak period and directionality were considered. Temporal variability in wave energy levels was particularly investigated for energy resource assessment. The major findings of this work include the narrow directional amplitude of the incident wave and higher significant wave heights of locally generated waves. The estimated energy resource levels agreed well with literature, also showing little annual fluctuation. The wave climate demonstrated to be in full agreement with the large-scale Equatorial Atlantic atmospheric variability, dominated by either local wind waves or by distant storm swells.© 2007 ASME

Collapse behaviour of intact and damaged deepwater pipelines and the influence of the reeling method of installation

Abstract Theoretical and experimental research on the ultimate strength of rigid pipelines for deepwater applications conducted at the Laboratory for Submarine Technology—COPPE has been reviewed. Small scale laboratory tests included intact pipes under external pressure combined with longitudinal bending as well as damaged pipes under external pressure. Results obtained from specialist computer programmes and analytical formulations have been correlated with experimental results in order to propose ultimate strength equations to be used in the design procedures. Aspects related to the pipeline installation by reeling method are considered.

Wave Energy Hyperbaric Device for Electricity Production

Wave energy is a renewable and non-polluting source and its use is being studied in different countries. The paper presents an overview on the harnessing of energy from waves and the activities associated with setting up a plant for extracting energy from waves in Port of Pecem, on the coast of Ceara State, Brazil. The technology employed is based on storing water under pressure in a hyperbaric chamber, from which a controlled jet of water drives a standard turbine. The wave resource at the proposed location is presented in terms of statistics data obtained from previous monitoring. The device components are described and small scale model tested under regular waves representatives of the installation region. Based on the experimental results values of prescribed pressures are identified in order to optimize the power generation.Copyright