Local Stress Assessment of Flexible Unbonded Pipes Using FEA

2012 ◽  
Author(s):  
Ben Edmans ◽  
Giulio Alfano ◽  
Hamid Bahai ◽  
Lakis Andronicou ◽  
Ali Bahtui
Keyword(s):  
Linear Models ◽  
Local Stress ◽  
External Pressure ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Finite Element Package ◽  
Bending Radius ◽  
Unbonded Flexible Pipes ◽  
The Individual ◽  
Computational Resources

Detailed stress analysis of unbonded flexible pipes has always been a challenging exercise which requires significant amount of computational resources and state of the art knowledge of flexible pipe modelling techniques. Lloyd’s Register EMEA and Brunel University have embarked on the development of a model which captures the response of the individual unbonded layers of flexible pipes using the ABAQUS finite element package employing 3D explicit and 3D implicit integration rules. The model accounts for nonlinear interaction between layers and provide the hysteresis response. The use of periodic boundary conditions to eliminate boundary effects at the pipe ends has also been investigated. The model predicts stress and strain conditions in metallic and plastic layers. These FEA predictions of the 3D non linear models are compared with the results of analytical methods for axisymmetric loads. This verification is carried out for three basic cases as follows: i) axial tension ii) internal/burst pressure iii) radial external pressure. Good agreement has been shown for stiffness and stress values predicted by the FEA and analytical formulations. Some initial results are presented for the bending behaviour in which the hysteresis obtained in the case of cyclic application of the design minimum bending radius is simulated.

Controlling Factors of Carcass Fatigue in Unbonded Flexible Pipes

2019 ◽  
Author(s):  
Upul S. Fernando ◽  
Andrew P. Roberts ◽  
Michelle Davidson
Keyword(s):  
Fatigue Failure ◽  
Failure Modes ◽  
Dynamic Stress ◽  
External Pressure ◽  
Controlling Factors ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Innermost Layer ◽  
Key Features ◽  
Unbonded Flexible Pipes

Abstract Carcass, the innermost layer of a flexible pipe structure is designed to prevent the collapse of the pressure sheath due to external pressure. Weakness, damage or failure of the carcass layer can result in collapse with associated loss of production and potentially serious risk to pipe integrity and hydrocarbon leakage to the environment. Avoiding carcass failure in service is therefore an essential consideration during the design of unbonded flexible pipes. Carcass failure is rare in service. This paper highlights the three possible failure modes and presents further analysis on the fatigue failure mode, relevant to dynamic service. Two key features of carcass manufacture are identified as causes for dynamic stress; locking of the carcass profile due to extended pitch and polymer ingress within the carcass cavity. Guidelines for the design of carcass profiles, setting safe pitch limits and appropriate barrier profile controls to mitigate carcass fatigue failure in dynamic service are presented.

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.

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.

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins
Keyword(s):  
Three Dimensional ◽  
External Pressure ◽  
Flexible Pipe ◽  
3D Fem ◽  
Collapse Pressure ◽  
Flexible Pipes ◽  
Polymeric Layer ◽  
Set Up ◽  
3D Finite Element Method ◽  
Ring Approximation

When submitted to high external pressure, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.

Prediction and Qualification of Radial Birdcage and Lateral Buckling of Flexible Pipes in Deepwater Applications

2015 ◽  
Author(s):  
Linfa Zhu ◽  
Zhimin Tan ◽  
Victor Pinheiro Pupo Nogueira ◽  
Jian Liu ◽  
Judimar Clevelario
Keyword(s):  
Failure Modes ◽  
Local Buckling ◽  
External Pressure ◽  
Design Guidelines ◽  
Prediction Theory ◽  
Flexible Pipe ◽  
Lateral Buckling ◽  
Operation Conditions ◽  
Flexible Pipes ◽  
Compressive Loads

Increasing oil exploitation in deepwater regions is driving the R&D of flexible pipes which are subjected to high external pressure loads from the hydrostatic head during their installation and operation. One of the challenges of flexible pipe design for such applications is to overcome the local buckling failure modes of tensile armor layers due to the combination of high external pressure, compressive loads and pipe curvature. This paper presents the latest progress in local buckling behavior prediction theory and the qualification process of flexible pipes. First, the mechanisms of two types of buckling behaviors, radial birdcage buckling and lateral buckling, are described. For each failure mode, the analytical buckling prediction theory is presented and the driving parameters are discussed. As part of the qualification process, the ability to resist radial birdcage and lateral buckling must be demonstrated. Suitable test protocols are required to represent the installation and operation conditions for the intended applications by deep immersion performance (DIP) tests. Several flexible pipes were designed based on radial birdcage and lateral buckling prediction theory, and pipe samples were manufactured using industrial production facilities for DIP tests. The results clearly show that flexible pipes following current design guidelines are suitable for deepwater applications. An alternative in-air rig was developed to simulate the DIP tests in a controlled laboratory environment to further validate the model prediction as a continuous development.

Calculation Methods of the Local Structure Behavior of Unbonded Flexible Pipes

2013 ◽  
Vol 658 ◽  
pp. 481-486
Author(s):  
Zhi Bo Li ◽  
Hui Xu ◽  
Gui Zhen Zhang
Keyword(s):  
Local Structure ◽  
Axial Load ◽  
Bending Moment ◽  
External Pressure ◽  
Nonlinear Relationship ◽  
Calculation Methods ◽  
Flexible Pipes ◽  
Bending Load ◽  
Unbonded Flexible Pipes ◽  
Moment Load

In this paper, the nonlinear relationship between the bending moment and curvature of non-bonded flexible pipes was studied. It was found that the relation was a function of internal and external pressure, axial force, and bending moment load. The model used in this paper took into consideration of the flexural, tensile and torsional strength of layers as well as the frictions between them. Symmetrical axial load was first applied, and then the bending load. Due to friction, the response of the unbonded flexible pipes is hysteretic to the loads. In conclusion, the response of unbonded flexible pipes are both related to its own structural properties and external loads.Coupling factors of different conditions should also be considered.

Analysis of Structural Parameters for Unbonded Flexible Pipes

2013 ◽  
Vol 652-654 ◽  
pp. 1514-1519
Author(s):  
Zhi Bo Li ◽  
Hui Xu ◽  
Gui Zhen Zhang
Keyword(s):  
Structural Parameters ◽  
Steel Strip ◽  
Complex Structure ◽  
Flexible Pipe ◽  
Complex Deformation ◽  
Flexible Pipes ◽  
Bending Behavior ◽  
Unbonded Flexible Pipes ◽  
Walled Cylinder ◽  
Nonuniform Material

Due to the complex structure and nonuniform material of unbonded flexible pipes, an elastic thin-walled cylinder model and a helical steel strip model were established respectively to simulate different layers based on the specific structure form and parameters. Quasi-static incremental load was adopted to identify the structural parameters which had significant effects on the axial, radial and bending behavior of the pipes during the complex deformation. Sensitivity of these parameters were also analysed. The conclusion in this paper could provide guaidance for the design of unbonded flexible pipe.

Lateral Buckling of Armor Wires in Flexible Pipes: Reaching 3000m Water Depth

2011 ◽  
Author(s):  
Philippe Secher ◽  
Fabrice Bectarte ◽  
Antoine Felix-Henry
Keyword(s):  
Deep Water ◽  
Failure Modes ◽  
External Pressure ◽  
Internal Diameter ◽  
Flexible Pipe ◽  
Lateral Buckling ◽  
Flexible Pipes ◽  
Valid Solution ◽  
Sour Service ◽  
Water Depths

This paper presents the latest progress on the armor wires lateral buckling phenomena with the qualification of flexible pipes for water depths up to 3,000m. The design challenges specific to ultra deep water are governed by the effect of the external pressure: Armor wires lateral buckling is one of the failure modes that needs to be addressed when the flexible pipe is empty and subject to dynamic curvature cycling. As a first step, the lateral buckling mechanism is described and driving parameters are discussed. Then, the program objective is presented together with flexible pipe designs: - Subsea dynamic Jumpers applications; - Sweet and Sour Service; - Internal diameters up to 11″. Dedicated flexible pipe components were selected to address the severe loading conditions encountered in water depths up to 3,000m. Hydrostatic collapse resistance was addressed by a thick inner carcass layer and a PSI pressure vault. Armor wires lateral buckling was addressed by the design and industrialization of new tensile armor wires. The pipe samples were manufactured using industrial production process in the factories in France and Brazil. The available testing protocols are then presented discussing their advantages and drawbacks. For this campaign, a combination of Deep Immersion Performances (DIP) tests and tests in hyperbaric chambers was selected. The DIP test campaign was performed End 2009 beginning 2010 in the Gulf of Mexico using one of Technip Installation Vessel. These tests replicated the actual design conditions to which a flexible pipe would be subjected during installation and operation. The results clearly demonstrated the suitability of flexible pipes as a valid solution for ultra deep water applications. In addition, the DIP tests results were compared to the tests in hyperbaric chambers giving consistent results. This campaign provided design limitations of the new designs for both 9″ and 11″ internal diameter flexible pipes, in sweet and sour service in water depths up to 3,000m.

Analysis of Mechanical Properties of Pipes with Helical Reinforcement under Axial Tension

2011 ◽  
Vol 189-193 ◽  
pp. 1822-1826 ◽  
Author(s):  
Wei Huang ◽  
Zhong You
Keyword(s):  
Mechanical Properties ◽  
Contact Pressure ◽  
Pitch Angle ◽  
External Pressure ◽  
Compatibility Equation ◽  
Flexible Pipe ◽  
Axial Tension ◽  
Flexible Pipes ◽  
Marine Engineering ◽  
Deformation Compatibility

Flexible pipes with helical reinforcement are widely used in the marine engineering and tissue engineering because of their low bending stiffness. Through appropriate design, they could also meet the strength requirement. All studies on this kind of structures regard the pitch angle of helical wires, strips or fibers as a vital parameter influencing the mechanical properties. In this study, we compare the tensile property of pipes with helical reinforcements braided in different initial pitch angles. Contact pressure is taken into consideration and eliminated by using deformation compatibility equation. The pitch angle changes under axial tension which induces the geometric nonlinearity. It is noted that when the pitch angle is larger than a critical value, even if there is no internal or external pressure, helixes will contact with the core under axial tension. But the initial pitch angle can not be too large since the contact pressure will induce partial buckling of the flexible pipe.

Sign in / Sign up

Export Citation Format

Share Document