scholarly journals A Theoretical Approach to Predict the Fatigue Life of Flexible Pipes

2012 ◽  
Vol 2012 ◽  
pp. 1-29 ◽  
Author(s):  
José Renato M. de Sousa ◽  
Fernando J. M. de Sousa ◽  
Marcos Q. de Siqueira ◽  
Luís V. S. Sagrilo ◽  
Carlos Alberto D. de Lemos
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Cross Section ◽  
Time Domain ◽  
Theoretical Approach ◽  
Flexible Pipe ◽  
Stress Effects ◽  
Flexible Pipes ◽  
Counting Methods ◽  
Mean Stresses

This paper focuses on a theoretical approach to access the fatigue life of flexible pipes. This methodology employs functions that convert forces and moments obtained in time-domain global analyses into stresses in their tensile armors. The stresses are then processed by well-known cycle counting methods, andS-Ncurves are used to evaluate the fatigue damage at several points in the pipe’s cross-section. Finally, Palmgren-Miner linear damage hypothesis is assumed in order to calculate the accumulated fatigue damage. A study on the fatigue life of a flexible pipe employing this methodology is presented. The main points addressed in the study are the influence of friction between layers, the effect of the annulus conditions, the importance of evaluating the fatigue life in various points of the pipe’s cross-section, and the effect of mean stresses. The results obtained suggest that the friction between layers and the annulus conditions strongly influences the fatigue life of flexible pipes. Moreover, mean stress effects are also significant, and at least half of the wires in each analyzed section of the pipe must be considered in a typical fatigue analysis.

Fatigue Analysis of a 6” Flexible Pipe With Broken Tensile Armor Wires

2012 ◽  
Author(s):  
José R. M. de Sousa ◽  
Fernando J. M. de Sousa ◽  
Marcos Q. de Siqueira ◽  
Luís V. S. Sagrilo ◽  
George Campello ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Mechanical Behavior ◽  
Fatigue Damage ◽  
Cross Section ◽  
Substantial Reduction ◽  
Fatigue Analysis ◽  
Flexible Pipe ◽  
Simple Set ◽  
Flexible Pipes ◽  
Counting Methods

This work focuses on a methodology to predict the fatigue life of flexible pipes with wires broken in their tensile armors. Initially, the mechanical behavior of these pipes is discussed. Relying on this discussion, a simple set of equations is proposed in order to calculate the stresses in the armors of these pipes. These equations employ pre-estimated linear coefficients to convert forces and moments that act on the pope into stresses. These stresses are then processed by well-known cycle counting methods and S-N curves are finally used to evaluate fatigue damage at several points in the pipe’s cross section. The use of this methodology is exemplified by the assessment of the fatigue life of a 6” flexible pipe in which 0 up to 5 wires of its outer tensile armor are broken. The results indicate a substantial reduction in the fatigue life of the pipe with the increasing number of wires broken.

A Theoretical Method to Estimate the Fatigue Life of Tensile Armors of Flexible Pipes

2018 ◽  
Author(s):  
Kaien Jiang ◽  
Yutian Lu ◽  
Yong Bai
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Theoretical Method ◽  
Mean Stress ◽  
Flexible Pipe ◽  
Friction Coefficients ◽  
Flexible Pipes ◽  
Damage Theory ◽  
Rainflow Counting

This paper mainly focuses on a theoretical methodology to calculate the fatigue life of tensile armor of flexible pipes. This approach employs the local model of flexible pipe that converts forces and moments obtained in time-domain global analyses into stresses in the spiral tendons of tensile armor layer. The stresses are then processed by rainflow counting methods, and S-N curves are adopted to evaluate the fatigue damage of tensile armors. Finally, Miner linear cumulative damage theory is used in order to calculate the accumulated fatigue damage. A case study on the fatigue life of a flexible pipe employing this methodology is presented, and the fatigue life of flexible pipe is obtained. The main points addressed in the study are the effect of mean stress and friction coefficients. The results indicate that the inner tensile armor at suspension point is the most prone to fatigue damage, in addition, mean stress correction and friction coefficients strongly influence the fatigue life of flexible pipes.

Fatigue Assessment of Concrete Members Strengthened by FRP Materials

2014 ◽  
Vol 617 ◽  
pp. 221-224 ◽  
Author(s):  
Alena Čavojcová ◽  
Martin Moravcik
Keyword(s):  
Fatigue Damage ◽  
Cross Section ◽  
Theoretical Approach ◽  
Material Properties ◽  
Beam Cross Section ◽  
European Standard ◽  
Fatigue Assessment ◽  
Concrete Members ◽  
Damage Structure ◽  
T Beam

Fatigue and fatigue damage leads to a change in material properties that can lead to the element failures. Generally, it is necessary to verify the influence of the fatigue effects on the concrete members according to European standard EC2, [1]. FRP materials have been possibly used for the fatigue damage structure rehabilitation. There we can apply the condition of the limit boundaries stress on concrete and limit force in FRP material theoretical approach. Fatigue assessment will be analyzed for T-beam cross section with reinforcement and strengthened FPR material in this paper.

Time Domain Fatigue Life Analysis of Offshore Jacket Structure

2019 ◽  
Author(s):  
Yan Wei Wu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time Domain ◽  
Offshore Wind ◽  
Support Structure ◽  
Structural Fatigue ◽  
Long Time ◽  
Fatigue Life Analysis ◽  
Stress Concentration Factors ◽  
The Time Domain

Abstract Offshore wind system encountered wind, wave, current, soil, and other environmental loads. The support structure is randomly loaded for a long time, which is more likely to cause fatigue damage. In this paper, the NREL 5MW wind turbine and OC4 jacket support structure is selected to perform the time domain fatigue analysis. Commercial software Bladed and SACS are used to perform the required structural responses and fatigue strength calculations. The Stress Concentration Factors (SCF) and S-N curves for the stress calculations of tubular joints are adopted based on the recommendation of DNV GL guidelines. The magnitude of the stress variation range and the corresponding number of counts are obtained by using the rain-flow counting algorithm. Finally, the Palmgren-Miner’s rule is adopted to calculate the cumulative damage ratio and the fatigue life can then be estimated. Fatigue damage ratio and structural fatigue life of each joint during 20 years of operation period are evaluated.

An Experimental and Numerical Investigation of the Effect of Axial Thermal Gradients in Flexible Pipes

2017 ◽  
Author(s):  
Dag Fergestad ◽  
Frank Klæbo ◽  
Jan Muren ◽  
Pål Hylland ◽  
Tom Are Grøv ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Cross Section ◽  
Measurement Techniques ◽  
Full Scale ◽  
Model Complexity ◽  
Flexible Pipe ◽  
Element Analysis ◽  
Flexible Pipes ◽  
Full Scale Testing

This paper discusses the structural challenges associated with high axial temperature gradients and the corresponding internal cross section forces. A representative flexible pipe section designed for high operational temperature has been subject to full scale testing with temperature profiles obtained by external heating and cooling. The test is providing detailed insight in onset and magnitude of relative layer movements and layer forces. As part of the full-scale testing, novel methods for temperature gradient testing of unbonded flexible pipes have been developed, along with layer force- and deflection-measurement techniques. The full-scale test set-up has been subject to numerous temperature cycles of various magnitudes, gradients, absolute temperatures, as well as tension cycling to investigate possible couplings to dynamics. Extensive use of finite element analysis has efficiently supported test planning, instrumentation and execution, as well as enabling increased understanding of the structural interaction within the unbonded flexible pipe cross section. When exploiting the problem by finite element analysis, key inputs will be correct material models for the polymeric layers, and as-built dimensions/thicknesses. Finding the balance between reasonable simplification and model complexity is also a challenge, where access to high quality full-scale tests and dissected pipes coming back from operation provides good support for these decisions. Considering the extensive full scale testing, supported by advanced finite element analysis, it is evident that increased attention will be needed to document reliable operation in the most demanding high temperature flexible pipe applications.

A Fast and Practical Method for Predicting the Fatigue Life of Offshore Wind Turbine Jacket Support Structures

2017 ◽  
Author(s):  
Chaoshuai Han ◽  
Yongliang Ma ◽  
Xianqiang Qu ◽  
Peijiang Qin ◽  
Binbin Qiu
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Time Domain ◽  
Practical Method ◽  
Computational Effort ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Support Structures

Fatigue assessment is a very important part in the design process of offshore wind turbine support structures subjected to wind and wave loads. Fully coupled time domain simulations due to wind and wave loads can potentially provide reliable fatigue predictions, however, it will take high computational effort to carry out fatigue analysis of the simultaneous wind and wave response of the support structure in time domain. For convenience and reducing computational efforts, a fast and practical method is proposed for predicting the fatigue life of offshore wind turbine jacket support structures. Wind induced fatigue is calculated in the time domain using ANSYS based on rainflow counting, and wave induced fatigue is computed in frequency domain using SACS based on a linear spectral analysis. Fatigue damage of X-joints and K-joints under combined environmental loads of wind and wave is estimated by using the proposed method. To verify the accuracy of the proposed formula, fatigue damage based on time domain rainflow cycle counting is calculated and can be considered as a reference. It is concluded that the proposed method provides reasonable fatigue damage predictions and can be adopted for evaluating the combined fatigue damage due to wind and wave loads in offshore wind turbine.

Prediction of Burst in Flexible Pipes

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins ◽  
Celso Pupo Pesce ◽  
Christiano Odir C. Meirelles ◽  
Eduardo Ribeiro Malta ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Cross Section ◽  
Plastic Material ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Material Model ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Equivalent Ring ◽  
Cross Section Profile

Usually when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded, as the first internal pressure resistance is given by the internal polymeric layer that transmits almost all the loading to the metallic pressure armor layer. The last one must be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. This paper presents three different numerical models and an analytical nonlinear model for determining the maximum internal pressure loading withstood by a flexible pipe without burst. The first of the numerical models is a ring approximation for the helically rolled pressure layer, considering its actual cross section profile. The second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The last numerical model is a two-dimensional (2D) simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The analytical model considers the pressure armor layer as an equivalent ring, taking into account geometrical and material nonlinear behaviors. Assumptions and results for each model are compared and discussed. The failure event and the corresponding stress state are commented.

scholarly journals On the Significance of the Higher-Order Stress in Riser Vortex-Induced Vibrations Responses

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Jie Wu ◽  
Decao Yin ◽  
Halvor Lie ◽  
Carl M. Larsen ◽  
Rolf J. Baarholm ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Flexible Pipe ◽  
Third Order ◽  
Higher Harmonics ◽  
The Third ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Vortex Shedding Frequency ◽  
Order Stress ◽  
The Impact

Vortex-induced vibrations (VIV) can lead to fast accumulation of fatigue damage and increased drag loads for slender marine structures. VIV responses mainly occur at the vortex shedding frequency, while higher harmonics can also be excited. Recent VIV model tests with flexible pipes have shown that higher harmonics in the crossflow (CF) direction can contribute to the fatigue damage significantly due to its higher frequency. Rigid cylinder experiments show that the CF third-order harmonics are more pronounced when the motion orbit is close to a “figure 8” shape and the cylinder is moving against the flow at its largest CF motion. However, there is still lack of understanding of when and where higher harmonics occur for a flexible pipe. Therefore, significant uncertainty remains on how to account for fatigue damage due to higher harmonics in VIV prediction. In the present paper, representative VIV data from various riser model test campaigns are carefully studied and analyzed. The key parameters that influence the magnitude of the third-order harmonic stress are found to be the bending stiffness, the reduced velocity, and the orbit stability. The experimental data are analyzed in order to assess the impact of each parameter on the third-order harmonic stress. A preliminary empirical response model to estimate the maximum CF third-order harmonic stress based on these identified structural and hydrodynamic parameters has been proposed. The results of this study will contribute to reduce the uncertainty and unnecessary conservatism in VIV prediction.

Corrosion Fatigue Behavior of Flexible Pipe Tensile Armor Wires in a CO2 Environment

2013 ◽  
Vol 758 ◽  
pp. 77-82 ◽  
Author(s):  
Fabio Santos ◽  
Fabio Pires ◽  
Richard Clements ◽  
Judimar Clevelario ◽  
Terry Sheldrake ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Corrosion Fatigue ◽  
New Technologies ◽  
Fatigue Behavior ◽  
Flexible Pipe ◽  
Vital Importance ◽  
Aggressive Environment ◽  
Flexible Pipes ◽  
Fatigue Life Reduction ◽  
Fatigue Experiment

The new offshore areas being explored in Brazil presents higher concentration of CO2 compared with most existing offshore fields. The presence of these more aggressive environments has led to the development of new technologies. Due to the construction characteristics of flexible pipes, any increase in CO2 concentration in the conveyed fluid will, in turn, increase the CO2 concentration in the pipe annulus, subjecting the metallic armor layers to a more aggressive environment. Evaluation of the CO2 effects of corrosion fatigue behavior in tensile armor wires is therefore of vital importance. A comprehensive corrosion fatigue experiment for tensile armor wires in environments up to 10 bar of CO2, has been established and the experimental results have shown a fatigue life reduction in the tensile amour wires due to higher levels of CO2.

Sign in / Sign up

Export Citation Format

Share Document