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.

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.

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.

Advanced Finite-Element Modeling for Creep Simulation on Flexible Pipe Pressure Sheath

2016 ◽  
Author(s):  
Jérôme Naturel ◽  
Thomas Epsztein ◽  
Thierry Gavouyère
Keyword(s):  
Finite Element ◽  
Full Range ◽  
Sensitivity Study ◽  
Small Scale ◽  
Main Function ◽  
Flexible Pipe ◽  
Creep Tests ◽  
Additional Information ◽  
Fea Model ◽  
Scale Test

Unbounded Flexible pipe used for offshore fields development are usually composed of different layers of polymer and steel, each layer having a specific function during the product service life. This multi-layer characteristic enables to tailor the cross-section of the pipe to meet project-specific requirement, and optimize the cost of the product for each application. In particular, the main function of the thermoplastic pressure sheath is to guaranty the sealing of the product. The material and the thickness of this pressure sheath mainly depend on the pressure and temperature of the bore, and the design choice is driven by the creeping of the sheath in the interstices of the pressure vault: it must be limited with regard to sheath thickness reduction, as per API17J design requirement. Consequently, when developing new material for pressure sheath application, the early prediction of the creep performance over the full range of the targeted application is crucial. For this reason, before any full-scale test, a test campaign is required to evaluate the creeping of the material on small-scale material sample. In this development context, the use of advanced finite-element simulation for predicting the creeping behavior is quite useful to amplify the benefit of tests campaign results, and to give additional information on material performances. As far as the modelling is validated by correlation with small-scale tests, the numerical tool is used to multiply virtual creep tests configurations. This paper will focus on the numerical challenges for developing such creeping simulation, based on ABAQUS commercial software. Firstly, the identification of the viscoelastoplastic parameters for polymer material law will be presented. This material law is a nonlinear viscoelastoplastic model consisting of multiple networks connected in parallel. The number of parameters of such law is not limited, but a compromise between law precision and identification robustness must be found. Then, the correlation process between small-scale test and finite-element results will be detailed. In particular, the influence of the experimental protocol has to be determined. Finally, a sensitivity study of the most influent parameters, based on parametric FEA model, will be presented to highlight the benefice of such model. The benefice of such model does not only consist on correlation with small-scale test. As the material modeling is intrinsic, it is also possible to use the same law for studying the creep behavior on very different geometrical configurations.

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.

Computational analysis of creep in ice and frozen soil based on Fish's unified model

1993 ◽  
Vol 20 (1) ◽  
pp. 120-132 ◽  
Author(s):  
U. G. A. Puswewala ◽  
R. K. N. D. Rajapakse
Keyword(s):  
Finite Element ◽  
Frozen Soil ◽  
Creep Model ◽  
Finite Element Code ◽  
Creep Tests ◽  
Frozen Soils ◽  
Uniaxial Creep ◽  
Media Interaction ◽  
Load Tests ◽  
Experimental Findings

The ability of the creep model of Fish to simulate the observed behaviour of ice and frozen soils in multiaxial stress-strain fields is investigated. The generalization of the original uniaxial creep model is made through the use of several assumptions and the multiaxial model is implemented in an iterative, time-incrementing finite element code. Sample creep parameters for the model are evaluated using previously reported uniaxial creep tests on ice and frozen silt. The finite element code is used to demonstrate the ability of the model to predict different stages of creep deformation in frozen media, by re-simulating some uniaxial creep tests on ice. Pressuremeter tests, plate load tests, and laterally loaded rigid cores (piles considered in cross section) in frozen media are simulated to demonstrate the similarity between the global response of ice and frozen soils predicted by the model and the reported experimental findings. Redistribution of stress predicted by the model is also investigated. The model is seen to possess validity in situations of attenuating as well as accelerating creep of ice and frozen soils. Key words: creep, ice, frozen soils, finite elements, structure–frozen media interaction, numerical prediction.

Analysis of the non-linear load and temperature-dependent creep behaviour of thermoplastic composite materials

2016 ◽  
Vol 30 (3) ◽  
pp. 302-317 ◽  
Author(s):  
Christian Brauner ◽  
Axel S Herrmann ◽  
Philipp M Niemeier ◽  
Konstantin Schubert
Keyword(s):  
Composite Materials ◽  
High Performance ◽  
Creep Behaviour ◽  
Full Range ◽  
Climatic Conditions ◽  
Thermoplastic Composite ◽  
Raw Material ◽  
Creep Model ◽  
Creep Tests ◽  
Non Linear

Fibre-reinforced thermoplastic composite materials can be manufactured rapidly using a thermoforming process. The assortment of thermoplastic matrix systems is manifold and starts from bulk plastic like polypropylene (PP) up to high-performance systems like polyether ether ketone. High-performance thermoplastic polymers have durable properties but relatively high raw material costs. For structural application, engineering methods are needed to ensure the availability for use over the full range of the life cycle of parts. This equates to at least 15 years under exposure to varying climatic conditions for an automobile component. Bulk plastics have complex viscoelastic behaviour, which means that advanced methods are needed to ensure the long-term behaviour of both the pure plastic or fibre-reinforced materials with such a matrix system. In the following study, the creep behaviour of a glass fibre-reinforced PP material is investigated using different uniaxially loaded creep tests at different load and temperature levels. Starting from this empirical base, two characteristic creep functions are derived using a modified Burgers approach. To transfer the results of uniaxial creep situations to a three-dimensional multiaxial stress state, a method to interpolate the experimental creep curves is presented. This developed creep model is integrated into the implicit non-linear finite element program SAMCEF/Mecano and used to predict the creep behaviour of a complex laminate. The results are then validated against the performed experiments.

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.

Periodic and Fixed Boundary Conditions for Multi-Scale Finite Element Analysis of Flexible Risers

2016 ◽  
Author(s):  
M. T. Rahmati ◽  
G. Alfano ◽  
H. Bahai
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Element Model ◽  
Small Scale ◽  
Flexible Pipe ◽  
Element Analysis ◽  
Time Saving ◽  
Flexible Risers

In this paper the implementation of two types of boundaries, periodic and fixed in-plane boundaries, for a detailed finite-element model of flexible risers is discussed. By using three-dimensional elements, all layer components are individually modelled and a surface-to-surface frictional contact model is used to simulate their interaction. The approach is applied on several riser models with various lengths and layers. It is shown that the model with periodic boundaries can be effectively employed in a fully-nested (FE2) multiscale analysis based on computational homogenization. In fact, in this model only a small fraction of a flexible pipe is needed for a detailed nonlinear finite-element analysis at the small scale. The advantage of applying periodic boundary conditions in capturing the detailed nonlinear effects and the efficiencies in terms of significant CPU time saving are demonstrated.

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.

scholarly journals On the interpretation of results from small punch creep tests

2010 ◽  
Vol 45 (3) ◽  
pp. 141-164 ◽  
Author(s):  
T H Hyde ◽  
M Stoyanov ◽  
W Sun ◽  
C J Hyde
Keyword(s):  
Finite Element ◽  
Creep Behaviour ◽  
Test Material ◽  
Complex Nature ◽  
Small Punch Test ◽  
Creep Tests ◽  
Linear Processes ◽  
Small Punch ◽  
Punch Test ◽  
Uniaxial Creep

The small punch creep testing method is highly complex and involves interactions between a number of non-linear processes. The deformed shapes that are produced from such tests are related to the punch and specimen dimensions and to the elastic, plastic, and creep behaviour of the test material, under contact and large deformation conditions, at elevated temperature. Owing to its complex nature, it is difficult to interpret the small punch test creep data in relation to the corresponding uniaxial creep behaviour of the material. One of the aims of this paper is to identify the important characteristics of the creep deformation resulting from ‘localized’ deformations and from the ‘overall’ deformation of the specimen. Following this, the results of approximate analytical and detailed finite element analyses of small punch tests are investigated. It is shown that the regions of the uniaxial creep test curves dominated by primary, secondary, and tertiary creep are not those that are immediately apparent from the displacement versus time records produced during a small punch test. On the basis of the interpretation of the finite element results presented, a method based on a reference stress approach is proposed for interpreting the results of small punch test experimental data. Future work planned for the interpretation of small punch tests data is briefly addressed.

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