Tensile strength of the unbonded flexible pipes

2019 ◽  
Vol 218 ◽  
pp. 142-151 ◽  
Author(s):  
Francesco Cornacchia ◽  
Ting Liu ◽  
Yong Bai ◽  
Nicholas Fantuzzi
Keyword(s):  
Tensile Strength ◽  
Flexible Pipes ◽  
Unbonded Flexible Pipes

Data Collection and Analysis for the Creation of a Digital Shadow During the Production of Thermoplastic Composite Layers in Unbonded Flexible Pipes

2018 ◽  
Author(s):  
Martin Schäkel ◽  
John McNab ◽  
Neville Dodds ◽  
Tido Peters ◽  
Henning Janssen ◽  
...  
Keyword(s):  
External Pressure ◽  
Thermoplastic Composite ◽  
Sensor Data ◽  
Consolidation Process ◽  
Specific Strength ◽  
Additional Information ◽  
Flexible Pipes ◽  
Potential Part ◽  
Path Dependent ◽  
Unbonded Flexible Pipes

Unbonded flexible pipes present a mature technology for the efficient recovery and transport of hydrocarbons offshore. The substitution of metallic reinforcement layers in the multi-layered structure by thermoplastic fiber-reinforced polymer (FRP) presents a solution for self-weight issues of especially long pipes, as FRP materials display high specific strength and modulus while being resistant to external pressure and corrosion. The production of these layers is automated by the laser-assisted tape winding process without the need of additional curing steps. During the manufacturing process, several data like process temperature and consolidation pressure are continuously monitored by non-contact sensors to ensure process stability without interfering in the consolidation process. To gain additional information about the temperature distribution within the multi-layered laminate, contact temperature sensors were introduced in the tape winding process. By this method the temperature of subjacent tapes can be assessed during the continued winding process. Additionally, this paper features a new approach of utilizing winding path data for relating the time-dependent sensor data to the exact position on the produced part. The visualization of path-dependent sensor data opens up possibilities of linking quality monitoring results to manufacturing insufficiencies and potential part defects.

Non-metallic Unbonded Flexible Pipes for Deepwater

2007 ◽  
Author(s):  
Mike Bryant ◽  
Shankar U. Bhat ◽  
Bin Chen
Keyword(s):  
Flexible Pipes ◽  
Unbonded Flexible Pipes

An Analytical Model to Predict the Bending Behavior of Unbonded Flexible Pipes

2013 ◽  
Vol 57 (03) ◽  
pp. 171-177
Author(s):  
Leilei Dong ◽  
Yi Huang ◽  
Qi Zhang ◽  
Gang Liu
Keyword(s):  
Bending Moment ◽  
Bending Stiffness ◽  
Nonlinear Formulation ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Bending Behavior ◽  
Interlayer Slip ◽  
Unbonded Flexible Pipes ◽  
Relationship Of ◽  
Theoretical Results

Analytical formulations are presented to determine the bending moment-curvature relationship of a helical layer in unbonded flexible pipes. Explicit expressions describing the variation of both bending stiffness and moment as a function of the applied curvature are given. The approach takes into account the nonlinearity of the response caused by the interlayer slip. The contribution of local bending and torsion of individual helical elements to the bending behavior of helical layers is included. Theoretical results for a typical unbonded flexible pipe using the nonlinear formulation for helical layers are compared with experimental data from the available literature. Encouraging correlations are found and the importance of the initial interlayer pressures is seen. The influence of local bending and torsion of individual helical elements on the bending behavior of the entire pipe is also evaluated. The results show that the inclusion of this local behavior significantly influences the full-slip bending stiffness.

Qualification Approach to Unbonded Flexible Pipes With Fibre Reinforced Armour Layer

2004 ◽  
Author(s):  
Jan Rytter
Keyword(s):  
Offshore Structure ◽  
Flexible Pipe ◽  
Load Bearing ◽  
Compression Load ◽  
Metal Parts ◽  
Analysis Tools ◽  
Industry Standards ◽  
Flexible Pipes ◽  
Unbonded Flexible Pipes ◽  
Load And Resistance Factor

The future water depth capabilities for unbonded flexible pipes is being pushed by NKT Flexibles I/S through the development of an innovative flexible pipe structure, taking full advantage of the material characteristics of metallic, polymeric and fibre reinforced materials. The fluid tight liner and possible insulation of this pipe structure are supported by an inner armour, capable of carrying the external hydrostatic pressure, clamp and crushing loads, as well as axial compression load, and an outer armour, consisting of two cross wound layers of carbon/epoxy composites, carrying the internal pressure as well as end cap forces and applied tension. A permeable and radially flexible outer layer protects the composite armour. Combining known and well-proven flexible pipe technologies and new solutions for materials, structure and functionality of the flexible pipe, positions this future product outside the present industry standards for flexible pipes, e.g. API-17J. The analysis tools used for the conventional flexible pipes are validated by NKT according to the API-17J specification. The API-17J describes load cases and corresponding allowable utilization ratios, stated as design criteria. However, this approach is not directly applicable to the composite pipe, where the same analysis tools will be used, but the material in one of the two primary load bearing layers is made of fibre reinforced polymer, a material class not covered by the API allowable utilization factors. The DNV offshore standard DNV-OS-C501 considers any offshore structure in which the load bearing material is a composite. An accompanying Recommended Practice DNV-RP-F202 for composite risers has also been issued, but is not applicable to the composite flexible pipe. The design equations of the DNV standard are formulated in the so-called Load and Resistance Factor Design (LRFD) format, where partial safety factors are applied to the load effects and to the resistance variables that enter the design equations. The DNV standard DNV-OS-C501 covers composite materials and composite metal interfaces of a structure, metal parts should be designed according to other relevant standards. The API standard can therefore be used for the metal parts. One of the challenges in using this combined approach is the different ways loads are defined in the two standards. In short, this will result in a conventional API design check of the inner armour, the polymer layers, and the secondary layers, whereas the composite tensile armour, special intermediate layers and the interfaces will be analyzed with composite specific tools based on the criteria derived from the DNV standard. The qualification procedure is described and exemplified in the following.

Characterizing the Wave Environment in the Fatigue Analysis of Flexible Risers

2005 ◽  
Vol 128 (2) ◽  
pp. 108-118 ◽  
Author(s):  
John M. Sheehan ◽  
Frank W. Grealish ◽  
Annette M. Harte ◽  
Russell J. Smith
Keyword(s):  
Cost Effective ◽  
Critical Issue ◽  
Fatigue Analysis ◽  
Flexible Pipes ◽  
Water Developments ◽  
Key Issues ◽  
Flexible Risers ◽  
Offshore Industry ◽  
Unbonded Flexible Pipes

As the offshore industry moves towards deeper water developments and continues to embrace harsh environments, unbonded flexible pipes are increasingly being utilized as a cost effective riser solution. Furthermore, with the advent of issues such as nonpristine annuli environments, the fatigue performance of these flexible risers is becoming a critical issue. This paper presents an overview of the comparisons between deterministic and stochastic global fatigue analysis techniques. Methods used to perform both deterministic and stochastic analyses are outlined, from performing the global analyses to using local models to generate armor wire stresses and subsequent fatigue damage. The paper identifies the key issues in the analysis performed and presents key results and conclusions with regard to the characterization of the wave environment in the global fatigue analysis of flexible risers.

A general model to predict torsion and curvature increments of tensile armors in unbonded flexible pipes

2019 ◽  
Vol 67 ◽  
pp. 102632 ◽  
Author(s):  
Leilei Dong ◽  
Zixin Qu ◽  
Qi Zhang ◽  
Yi Huang ◽  
Gang Liu
Keyword(s):  
General Model ◽  
Flexible Pipes ◽  
Unbonded Flexible Pipes

Numerical investigation of friction joint between Basalt Fiber Reinforced Composites and aluminum

2016 ◽  
Vol 231 (5) ◽  
pp. 543-551
Author(s):  
Andrei Costache ◽  
Christian Berggreen ◽  
Ion Marius Sivebæk ◽  
Kristian Glejbøl
Keyword(s):  
Finite Element ◽  
Basalt Fiber ◽  
Element Model ◽  
Fiber Reinforced ◽  
Pullout Force ◽  
Flexible Pipes ◽  
The Coefficient Of Friction ◽  
Flexible Risers ◽  
Offshore Oil Industry ◽  
Unbonded Flexible Pipes

Flexible risers are used in the offshore oil industry for exporting hydrocarbons from subsea equipment to floating production and storage vessels. The latest research in unbonded flexible pipes aims to reduce weight by replacing metal components with composite materials. This would result in lighter and stiffer flexible risers, which would be well suited for ultra deep water applications. This paper develops a new finite element model used for evaluating the efficiency of anchoring flat unidirectional fiber reinforced tendons in a mechanical grip. It consists two flat grips with the fiber reinforced tendon in between. The grips are pressed against the composite and the pullout force is ensured through friction. The novelty of the paper is represented by the detailed investigation of the influence between the coefficient of friction and the pullout force. By comparing numerical and experimentally obtained results, it is possible to show the importance of friction decay in the grip. Improper contact between the grips and composite is also taken into account and leads to good agreement between numerical and experimental results. This study shows how to avoid over-estimating the efficiency of such grip by using dry friction in finite element models.

End Fitting Effect on Stress Evaluation of Tensile Armor Tendons in Unbonded Flexible Pipes Under Axial Tension

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Leilei Dong ◽  
Qi Zhang ◽  
Yi Huang ◽  
Gang Liu ◽  
Zhiyuan Li
Keyword(s):  
Lateral Displacement ◽  
Axial Strain ◽  
Supplementary Condition ◽  
Bending Stress ◽  
Stress Evaluation ◽  
Axial Tension ◽  
Flexible Pipes ◽  
Helical Angle ◽  
The Wire ◽  
Unbonded Flexible Pipes

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives the lateral displacement of the wire, which is determined by minimizing the energy functional that consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is verified with a finite element (FE) simulation. Comparisons between the model predictions and the FE results in terms of the change in helical angle and transverse bending stress show good correlations. The verified model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear, and friction could significantly increase the stress at the end fitting compared with the frictionless case.

An Analytical Model to Predict the Bending Behavior of Unbonded Flexible Pipes

2013 ◽  
Vol 57 (3) ◽  
pp. 171-177 ◽  
Author(s):  
Leilei Dong ◽  
Yi Huang ◽  
Qi Zhang ◽  
Gang Liu
Keyword(s):  
Analytical Model ◽  
Flexible Pipes ◽  
Bending Behavior ◽  
Unbonded Flexible Pipes

Measurement of Residual Stress Shakedown in Pressure/Tensile Armour Wires of Flexible Pipes by Neutron Diffraction

2015 ◽  
Author(s):  
Upul S. Fernando ◽  
Michelle Davidson ◽  
Christopher Simpson ◽  
Thilo Pirling ◽  
Kun Yan ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Metal Layer ◽  
Diffraction Method ◽  
Acceptance Test ◽  
Flexible Pipes ◽  
Before And After ◽  
Unbonded Flexible Pipes ◽  
Hoop Stresses

The manufacture of unbonded flexible pipes (flowlines and risers) involves wrapping steel wires to create pressure and tensile armour layers. The forming of armour wires from vendor supply conditions to a helix shape on the pipe involves significant plastic straining and the wires that are wrapped onto the pipe are not unloaded. Therefore the armour wires in flexible pipes are expected to contain significant residual stress (RS) as a result of the plastic straining and loading during manufacture and placement. This may lead to detrimental effects on the strength, durability and the service integrity of the pipe. It is postulated that the unfavorable RS introduced during pipe manufacture reduces due to stress shakedown during the factory acceptance test (FAT) where the pipe is subjected to a high internal pressure. This paper describes the first attempts to measure RS in the armour wires in unbonded flexible pipes. The key development is the use of a neutron diffraction method which allows the measurement of RS in-situ on the manufactured pipe through the whole wire sections. Pipe samples were prepared exposing the relevant metal layer and the measurements were performed on pipe samples taken before and after performing the pressurized FAT. The effect of the FAT on the shakedown of residual stress in pressure armour wires is discussed. As shown by the measurements, the elastic strains and stresses in the pressure armour wires are much larger in the hoop direction of the pipe (i.e. along the length of the wire) than radial or axial to the pipe. In pre-FAT pipe the hoop stresses are essentially tensile on the extrados and compressive on the intrados. The results have shown that the FAT reduces the hoop strains and stresses to approximately 1/3 of their as manufactured level.

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