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.

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.

Evaluating the Coupledness of the Aerodynamics and Hydrodynamics on the Estimation of Fatigue Damage Equivalent Load for a Floating Offshore Wind Platform

2018 ◽  
Author(s):  
Samuel Kanner ◽  
Bingbin Yu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Environmental Conditions ◽  
Offshore Wind ◽  
Coupled Analysis ◽  
Offshore Wind Turbine ◽  
Wave Conditions ◽  
Equivalent Load ◽  
The Waves

In this research, the estimation of the fatigue life of a semi-submersible floating offshore wind platform is considered. In order to accurately estimate the fatigue life of a platform, coupled aerodynamic-hydrodynamic simulations are performed to obtain dynamic stress values. The simulations are performed at a multitude of representative environmental states, or “bins,” which can mimic the conditions the structure may endure at a given site, per ABS Floating Offshore Wind Turbine Installation guidelines. To accurately represent the variety of wind and wave conditions, the number of environmental states can be of the order of 103. Unlike other offshore structures, both the wind and wave conditions must be accounted for, which are generally considered independent parameters, drastically increasing the number of states. The stress timeseries from these simulations can be used to estimate the damage at a particular location on the structure by using commonly accepted methods, such as the rainflow counting algorithm. The damage due to either the winds or the waves can be estimated by using a frequency decomposition of the stress timeseries. In this paper, a similar decoupled approach is used to attempt to recover the damages induced from these coupled simulations. Although it is well-known that a coupled, aero-hydro analysis is necessary in order to accurately simulate the nonlinear rigid-body motions of the platform, it is less clear if the same statement could be made about the fatigue properties of the platform. In one approach, the fatigue damage equivalent load is calculated independently from both scatter diagrams of the waves and a rose diagram of the wind. De-coupled simulations are performed to estimate the response at an all-encompassing range of environmental conditions. A database of responses based on these environmental conditions is constructed. The likelihood of occurrence at a case-study site is used to compare the damage equivalent from the coupled simulations. The OC5 platform in the Borssele wind farm zone is used as a case-study and the damage equivalent load from the de-coupled methods are compared to those from the coupled analysis in order to assess these methodologies.

Fatigue Analysis of Metallic Strips Flexible Pipe

2018 ◽  
Author(s):  
Guowei Sun ◽  
Peihua Han ◽  
Yuxin Xu ◽  
Yong Bai ◽  
Hamad Hameed
Keyword(s):  
Fatigue Life ◽  
Global Analysis ◽  
Element Model ◽  
Dynamic Responses ◽  
Flexible Pipe ◽  
Steel Strips ◽  
Counting Algorithms ◽  
Marine Engineering ◽  
Rainflow Counting ◽  
Specific Working

Metallic strips flexible pipe (MSFP) is widely regarded as an alternative for submarine pipelines. This paper presents a methodology for calculating the fatigue life of MSFP. Firstly, given a specific working condition of MSFP, the dynamic responses of MSFP are calculated through OrcaFlex. The obtained results from the global analysis are then implemented into a finite element model in ABAQUS to determine the stress-history curves of each steel strips layer. The estimated fatigue life is calculated by rainflow counting algorithms, S-N curve and Miner’s rule which are coded in MATLAB. Additional study about average stress correction is carried out, which might be useful for its marine engineering applications.

Finite Element Analysis of Flexible Pipes Under Axial Compression: Influence of the Sample Length

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Eduardo Ribeiro Malta ◽  
Clóvis de Arruda Martins
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Inner Core ◽  
High Sensitivity ◽  
Element Model ◽  
Sample Length ◽  
Flexible Pipe ◽  
Element Analysis ◽  
Flexible Pipes

In order to study the axial compressive behavior of flexible pipes, a nonlinear tridimensional finite element model was developed. This model recreates a five layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape, and a rigid inner core. Using this model, several studies were conducted to verify the influence of key parameters on the wire instability phenomenon. The pipe sample length can be considered as one of these parameters. This paper includes a detailed description of the finite element model itself and a case study where the length of the pipe is varied. The procedure of this analysis is here described and a case study is presented which shows that the sample length itself has no practical effect on the prebuckling response of the samples and a small effect on the limit force value. The postbuckling response, however, presented high sensitivity to the changes, but its erratic behavior has made impossible to establish a pattern.

Direct Calculation of Fatigue Damage of Ship Structure Details

2011 ◽  
Author(s):  
Zhiyuan Li ◽  
Jonas W. Ringsberg
Keyword(s):  
Fatigue Damage ◽  
Time Domain ◽  
Direct Calculation ◽  
Fatigue Analysis ◽  
Fe Model ◽  
Stress Concentration Factors ◽  
Rainflow Counting ◽  
Global And Local

Fatigue assessment of ships using the direct calculation approach has been investigated by numerous researchers. Normally, this approach is carried out as either a global model analysis, or as a local model structural analysis. The current investigation presents a case study of a container vessel where the global and local analyses procedures are combined. A nonlinear time-domain hydrodynamic analysis followed by a global FE analysis is employed to screen for the most severe locations of the global ship’s hull with regard to fatigue damage. Once these locations have been identified, a sub-modelling technique is employed to transfer global loads from the global FE model to local FE models that have high resolution of elements for local structure details. Results from a selection of local FE model simulations are presented. Stress concentration factors at four critical locations are calculated and compared with values recommended by classification guidelines. Results are presented from a short-term fatigue analysis which has been carried out using the rainflow counting method. Finally, a long-term fatigue analysis is performed in time-domain using a designed wave scatter diagram of representative sea states.

Numerical study of fatigue damage under random loading using Rainflow cycle counting

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Tayeb Kebir ◽  
José A.F.O. Correia ◽  
Mohamed Benguediab ◽  
Abilio M.P. De Jesus
Keyword(s):  
Fatigue Damage ◽  
Numerical Study ◽  
Scientific Work ◽  
Stress Effect ◽  
Mean Stress ◽  
Random Loading ◽  
Content Type ◽  
Rainflow Cycle Counting ◽  
The Mean ◽  
Rainflow Counting

PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading, taking into account the mean stress effect on fatigue lifetime and using the Rainflow counting technique to assess the fatigue damage by the Ansys software. The used material is aluminum alloy 6082-T6. A comparison with literature results has confirmed this investigation in this paper.Design/methodology/approachThe study of fatigue under random loading is based on the same concepts as constant loading with the addition of damage summation. The proportion of damage caused by a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsAnalysis of the fatigue damage shows that the number of relative damage due to each cycle.Originality/valueThis paper aims to simulate the fatigue damage under random loading for aluminum alloys.

Bi-Probability Fatigue Life Prediction for Bridge Crane Structures

2012 ◽  
Vol 482-484 ◽  
pp. 736-740
Author(s):  
Xiao Mei ◽  
Da Shan Dong ◽  
Yuan Yuan Teng
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Prediction Method ◽  
Steel Structures ◽  
Fatigue Life Prediction ◽  
Bridge Crane ◽  
Stress Cycle ◽  
Damage Theory ◽  
Rainflow Counting ◽  
Position Probability

Fatigue crack is very dangerous for safely operating of steel structures. To estimate precisely fatigue life of bridge cranes, the randomness of lifted load and trolley’s position should be considered. Therefore, bi-probability fatigue life prediction method, namely load and position probability, is put forward based on the miner linear cumulative damage theory. Stress cycle spectrum is constructed based on real-time monitoring data by rainflow counting method. This method can successfully explain the existence of girder cracks in a typical bridge crane RMG, so it would provide valuable reference for maintenance decision of in-service cranes.

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