Analysis of the Creep Behaviour of the Polymer Barrier Layer in Unbonded Flexible Pipes Under Different Fluid Temperatures

2012 ◽  
Author(s):  
Yijun Shen ◽  
Jian Zhao ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Finite Element ◽  
Polymer Material ◽  
Barrier Layer ◽  
Creep Behaviour ◽  
Polymer Materials ◽  
Creep Model ◽  
Implicit Time ◽  
Small Scale ◽  
Flexible Pipes ◽  
Unbonded Flexible Pipes

This paper discusses the influence of different fluid temperatures on the creep behaviour of the polymer barrier inside unbonded flexible pipes. The creep behaviour of the polymer material is generally time-dependent and associated with larger, nonlinear deformation. Excessive creep deformation may lead to structural failure, due to the over-reduction of the barrier layer thickness, and is therefore an important design consideration in ensuring the structural integrity of this layer. Creep behaviour in polymer material is complex, as it is governed by a number of variables, such as the stress/strain state, temperature, and pressure for example. This paper deals with the influence of different fluid temperatures on the creep behaviour of the polymer barrier layer under pipe design pressures, particularly in high temperature fluid transportation pipelines for deep or ultra-deep sea applications. The analysis model was established using commercial finite element software ANSYS, where an implicit time hardening creep model, based on the Maxwell viscoelastic model, was selected to represent the creep behaviour of the polymer materials. The coefficients of the implemented polymer material gap span creep model are calibrated to represent the worst case of the small-scale sample gap span creep tests performed in-house. A comparison is made between the simulation results of the calibrated gap span creep model and the corresponding small-scale creep test measurements. The experimental test results and the finite element modelling results show good correlation. This demonstrates that the creep model predictions are conservative for the polymer material of the barrier layer inside an unbonded flexible pipe.

Influence of Bore Pressure on the Creep Behaviour of Polymer Barrier Layer Inside an Unbonded Flexible Pipe

2011 ◽  
Author(s):  
Yijun Shen ◽  
Jian Zhao ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Finite Element ◽  
Polymer Material ◽  
Barrier Layer ◽  
Creep Behaviour ◽  
Polymer Materials ◽  
Creep Model ◽  
Implicit Time ◽  
Small Scale ◽  
Flexible Pipe ◽  
Creep Tests

This paper investigates the influence of bore pressure, combined with the nonlinear behaviour of the polymer material, on the creep behaviour of the polymer barrier layer inside an unbonded flexible pipe. Creep behaviour in the barrier layer may result in its reduction in thickness and is therefore an important design consideration in ensuring the structural integrity of this layer. It is meaningful to study the variation in creep behaviour in an unbonded flexible pipe under different bore pressures and temperatures, especially in high pressure pipelines for deep or ultra-deep sea applications. Creep behaviour in polymer material is complex, as it is governed by a number of variables such as the stress/strain state, temperature, and pressure for example. It is generally time-dependent and often associated with larger strains or states of deformation. Owing to the complexity of polymer material creep, an implicit time hardening creep model, based on the Maxwell viscoelastic model, has been selected to represent the creep behaviour in polymer materials and implemented into the Gap Span model, which is an in-house ANSYS based finite element model. The coefficients of this creep model were initially calibrated according to standard creep tests performed on polymer materials. The study presented in this paper focuses on the influence of bore pressure and high temperature on the creep behaviour of the polymer barrier layer. Comparisons between the simulation results of the calibrated Gap Span creep model and the corresponding small-scale creep tests demonstrate that these model predictions are overly conservative for the polymer material of the barrier layer inside an unbonded flexible pipe. Comparisons between the experimental test results and the finite element modelling results show good correlation.

Creep Analysis for an Unbonded Flexible Pipe Barrier

2006 ◽  
Author(s):  
Lun Qiu ◽  
John Zhang
Keyword(s):  
Finite Element ◽  
Creep Behavior ◽  
Barrier Layer ◽  
Polyvinylidene Fluoride ◽  
Element Model ◽  
Polymer Materials ◽  
Flexible Pipe ◽  
Internal Fluid ◽  
Creep Analysis ◽  
Parameter Matching

The fluid barrier in an unbonded flexible pipe seals the pressure from the internal fluid. Since the barrier is usually made of polymer materials, it is unable to hold the pressure by itself. A metal reinforced hoop layer is usually needed outside the barrier layer in order to resist the pressure. The hoop layer is usually a steel bar with a cross-section of an irregular shape. It is helically wrapped at the outside of the barrier layer. When the pipe is pressurized, the barrier will be supported by the hoop reinforcement layer from outside. However, at the gap between the steel wraps where the barrier layer bridges, material of the barrier will be forced to extrude into the gap. The amount of the extrusion is a function of many parameters such as temperature, material property, and internal pressure and so on. In addition, it is time dependent. The creep effect needs be considered. It is critical to have a proper barrier design for a flexible pipe structure. This article presents a practical finite element method for evaluation of the barrier/gap design. The creep behavior of the polymers is multi-parameter related. Therefore, a series of material tests has been conducted under various stresses and temperatures for nylon, polyethylene and Polyvinylidene Fluoride. In this work a method is given to determine the creep behavior parameters through parameter matching based on the tests. The creep deformation of barrier was analyzed with a finite element model using these parameters.

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.

Thermal Effects on the Anchoring of Flexible Pipe Tensile Armors

2015 ◽  
Author(s):  
Olaf O. Otte Filho ◽  
Rafael L. Tanaka ◽  
Rafael G. Morini ◽  
Rafael N. Torres ◽  
Thamise S. V. Vilela
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Thermal Effects ◽  
Current Model ◽  
Element Model ◽  
Small Scale ◽  
Flexible Pipe ◽  
System A ◽  
Flexible Pipes ◽  
Better Than

In the design of flexible pipes, predict the anchoring behavior on end fittings is always challenging. In this sense, Prysmian Surflex has developed a finite element model, which should help the end fitting design as well the prediction of the structural behavior and the acceptable maximum loads. The current model considers that the contact between armor-resin is purely cohesive and has been suitable for the design of end fittings [1] and [2]. But tests and new studies [3] and [4] indicate that only cohesive assumption would not be the best approach. Experimental data from prototype tests also show that the current model would not predict acceptable results for loads higher than those used in previous projects. This document will describe a study developed considering the friction and thermal contraction, instead of the cohesive phenomenon in the anchoring behavior analysis. Small scale tests were conducted in order to understand the anchoring relation between the resin and the wire used in the tensile armor. For this purpose, a special test device was developed to simulate an enclosure system. A parametric study was also performed to identify the cooling temperatures, coefficients of friction and contact properties parameters taken from small scale tests. The finite element model considers the thermal effects during exothermic curing. Using the new parameters obtained, a second model was developed. This model consists of only one real shaped bended wire inside an end fitting cavity. To validate the model, samples were tested on laboratory according anchoring design. The results of this round of tests were studied and corroborate the argument that use friction and thermal effects is better than use only the cohesive condition.

scholarly journals A practical creep model for concrete elements under eccentric compression

2019 ◽  
Vol 52 (6) ◽  
Author(s):  
Haidong Huang ◽  
Reyes Garcia ◽  
Shan-Shan Huang ◽  
Maurizio Guadagnini ◽  
Kypros Pilakoutas
Keyword(s):  
Prestressed Concrete ◽  
Creep Behaviour ◽  
Concrete Structures ◽  
Creep Model ◽  
Small Scale ◽  
Compressive Creep ◽  
Eccentric Compression ◽  
Shrinkage And Creep ◽  
Concrete Elements

AbstractMany prestressed concrete bridges are reported to suffer from excessive vertical deflections and cracking during their service life. Creep softens the structure significantly, and therefore an accurate prediction of creep is necessary to determine long-term deflections in elements under eccentric axial compression such as prestressed concrete girders. This study proposes a modification to the creep damage model of Model Code 2010 to account for the effect of load eccentricity. The modified creep model considers damage due to differential drying shrinkage. Initially, the creep behaviour of small scale concrete specimens under eccentric compression load is investigated experimentally. Twelve small-scale concrete prisms were subjected to eccentric axial loading to assess their shrinkage and creep behaviour. The main parameters investigated include the load eccentricity and exposure conditions. Based on the experimental results, an inverse analysis is conducted to determine the main parameters of the modified creep model. Subsequently, a numerical hygro-mechanical simulation is carried out to examine the effect of load eccentricity on the development of shrinkage and creep, and on the interaction between drying, damage and creep. The results indicate that eccentric loading leads to different tensile and compressive creep through the cross section, which contradicts the current design approach that assumes that tensile and compressive creep are identical. The proposed model also predicts accurately the long-term behaviour of tests on reinforced concrete elements available in the literature. This study contributes towards further understanding of the long-term behaviour of concrete structures, and towards the development of advanced creep models for the design/assessment of concrete structures.

Creep behaviour of a buffer material for nuclear fuel waste vault

1985 ◽  
Vol 22 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Raymond N. Yong ◽  
Prapote Boonsinsuk ◽  
Demos Yiotis
Keyword(s):  
Finite Element ◽  
Nuclear Fuel ◽  
Host Rock ◽  
Creep Behaviour ◽  
Creep Model ◽  
Secondary Creep ◽  
Full Size ◽  
Waste Container ◽  
Buffer Material ◽  
Nuclear Fuel Waste

In the Canadian nuclear fuel waste disposal concept currently under study, one of the prime candidate procedures is the borehole emplacement technique. Each fuel waste container will be placed in a 1.1 m diameter hole in the floor of a disposal vault in deep plutonic rock. The container will be surrounded by buffer material consisting of a mixture of clay and sand. This study examines the creep behaviour of the buffer material in the borehole during interaction with the waste container and the host rock. It simulated the buffer – container – host rock interaction through a small-scale physical model using the loading pressures anticipated in the full-size system. The results from the model tests were compared with those predicted by a finite element analytical model. The creep behaviour of the full-size system was then predicted using the analytical model.From the results, it is evident that the creep behaviour of the buffer material depends significantly on interaction within the container – buffer – host rock system, overburden pressure, and water uptake. At relatively low overburden pressures, the waste container might settle, causing a separation between the buffer material and the container top. However, this could be alleviated by the swelling properties of the buffer material. The secondary creep rates are negligible, and creep in the buffer material is primarily governed by the primary creep stage. Key words: creep, model test, swelling soil, soil deformation, unsaturated soil, finite element analysis.

Helical Wire Behavior of Unbonded Flexible Pipes Under Bending

2015 ◽  
Author(s):  
Yutian Lu ◽  
Huibin Yan ◽  
Yong Bai ◽  
Peng Cheng
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Axial Strain ◽  
Bending Moment ◽  
Element Model ◽  
Flexible Pipe ◽  
Slip Mechanism ◽  
Flexible Pipes ◽  
Bending Behavior ◽  
Unbonded Flexible Pipes

The bending behavior of unbonded flexible pipe is governed by the response of the helical wires in the tensile armor to bending. The behavior of the helical wire, especially the axial strain, is influenced by the slip mechanism as a result of an increasing curvature under bending. In the present paper, two limit curves are considered with a certain curvature. A 3-D finite element model using ABAQUS is developed to simulate the practical behavior of the helical wires under bending. By comparing the FEA and theoretical results, a basic conclusion about the real slip path of the helical wire between two limit curves is introduced. A hysteretic bending moment-curvature relationship induced by the slip mechanism is obtained from the finite element model as well.

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

2017 ◽  
Author(s):  
Leilei Dong ◽  
Qi Zhang ◽  
Yi Huang ◽  
Gang Liu ◽  
Zhiyuan Li
Keyword(s):  
Finite Element ◽  
Lateral Displacement ◽  
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 lateral displacement of the wire, which is determined by minimization of the energy functional 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 validated with a finite element simulation. Comparisons between the model predictions and the finite element results in terms of the change in helical angle and transverse bending stress show good correlations. The validated 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.

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