Stress Concentration Factors of Damaged FPSO Side Panels Under Cyclic Loads

2013 ◽  
Author(s):  
Ilson Pasqualino ◽  
Bianca Pinheiro ◽  
Carolina Ferreira
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Element Model ◽  
Compression Load ◽  
Life Study ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors

FPSO (floating production, storage and offloading) units can be subjected to mechanical damage in their side panels caused by collision with supply vessels. Even if the ultimate strength of the panel is not significantly affected by small damage, the stress concentration in the collided region may lead to the initiation of fatigue cracks, considering the long period of operation undergone by these vessels. The aim of this work is to evaluate stress concentration factors (SCFs) in damaged FPSO side panels and estimate their effect on the fatigue life through a theoretical study. A finite element model is developed to reproduce a supply vessel collision and evaluate resulting SCFs under in-plane compression load. A parametric study is carried out considering different damage magnitudes and the results obtained are used to develop an analytical expression to provide SCFs as a function of dimensions of damage and panel. SCFs provided by this expression could be used in a theoretical fatigue life study that can estimate the residual fatigue life of collided FPSO side panels and help to forewarn a fatigue failure under the event of an accidental collision.

Stress Concentration Factors of Dented Rigid Risers

2013 ◽  
Author(s):  
Bianca Pinheiro ◽  
Ilson Pasqualino ◽  
Nathália de Azevedo
Keyword(s):  
Stress Concentration ◽  
Fatigue Failure ◽  
Parametric Study ◽  
Element Model ◽  
Steel Catenary Riser ◽  
Life Study ◽  
Analytical Formulae ◽  
Concentration Factors ◽  
Offshore Industry ◽  
Stress Concentration Factors

Rigid risers are widely employed in the offshore industry nowadays, assuming the vertical (riser tower) or catenary (steel catenary riser, SCR) configurations. During operation, these structures undergo dynamic loads generated by the action of currents and waves. Rigid risers can also be subjected to collision from neighboring vessels or impact of heavy objects launched from them, resulting in the introduction of defects. The possibility of a fatigue failure must be addressed since these defects induce high localized stresses in the damaged section. The aim of this work is to evaluate the stress concentration induced by plain dents on rigid risers under combined dynamic bending and constant tension loads. A finite element model is developed to reproduce denting and spring back processes and estimate the stress concentration on the dented riser under combined bending and tension loads. The model is used in a parametric study to evaluate stress concentration factors (SCFs) for varying dimensions of dents and risers. Analytical formulae are developed considering the results from the parametric study to estimate SCFs of dented risers, which can be used in a theoretical fatigue life study, modifying standard S-N curves, and help to forewarn a fatigue failure.

Assessment of Stress Concentration Factors of Dented Rigid Risers under Fatigue Loadings

2021 ◽  
pp. 1-11
Author(s):  
Elvis Santander ◽  
Bianca Pinheiro ◽  
Carlos Magluta ◽  
Ney Roitman
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Element Model ◽  
Dimensional Finite Element ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Three Dimensional Finite Element

Abstract In the development of oil and gas fields, subsea pipes are used in various applications, like pipelines and risers. During operation, risers can be subjected to accidents, such as collisions with other risers, anchors, rocks, or any heavy equipment or objects, which may lead to mechanical damages. These mechanical damages are commonly characterized as dents. The objective of this work is to study the effect of the introduction of plain dents on the fatigue life of rigid risers under fully reversed bending with the conduction of resonant bending tests. A three-dimensional finite element model was developed to estimate the stress concentration on dented risers under bending. Numerical simulations and experimental tests were carried out to evaluate the resulting stress concentration factors (SCFs). These SCFs can be used in the prediction of the remaining fatigue life of dented rigid risers.

3D Roughness Parameters as Factors in Determining the Evolution of Effective Stress Concentration Factors in Fatigue Processes

2012 ◽  
Vol 248 ◽  
pp. 504-510 ◽  
Author(s):  
Valentin Mereuta ◽  
Mihaela Buciumeanu ◽  
Liviu Palaghian
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Effective Stress ◽  
Roughness Parameters ◽  
Machined Surface ◽  
Machined Surface Roughness ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Effective Stress Concentration Factor

The influence of machined surface roughness on the fatigue life of S355JR steel has been investigated. The specimen have been machined with three roughness levels and tested under plane fatigue. The surface roughness parameters were used to estimate the effective stress concentration factors Kt using the Arola-Ramulu model and Neuber model. In this paper it is proposed a modification for both models. Based on the experimental results was obtained the evolution of the effective stress concentration factor for the original Arola-Ramulu and Neuber models and also for the modified ones.

Fatigue Assessment of Dented Rigid Risers

2019 ◽  
Author(s):  
Elvis J. O. Santander ◽  
Bianca Pinheiro ◽  
Carlos Magluta ◽  
Ney Roitman
Keyword(s):  
Stress Concentration ◽  
Structural Integrity ◽  
Three Dimensional ◽  
Element Model ◽  
Oil Fields ◽  
Dimensional Finite Element ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Three Dimensional Finite Element ◽  
Remaining Fatigue Life

Abstract In the development of oil fields, submarine pipelines are used in various applications. These pipelines and risers are subject to accidents that may occur during operation, such as shocks between risers or shocks between a riser and an anchor, rock, or any equipment or heavy object, which may cause mechanical failure, such as dents. The objective of this work is to study of the effect of the introduction of plain dents on the structural integrity of rigid risers under fully reversed bending. A three dimensional finite element model was developed to estimate the stress concentration on dented risers under bending. Several numerical simulations were carried out to evaluate stress concentration factors (SCFs) for varying dimensions of dents and risers, in a parametric study. These SCFs can be used in the prediction of the remaining fatigue life of dented rigid risers.

Fatigue Assessment of Damaged Pipelines After Glass Fiber and Epoxy Matrix Laminate Repairs

2017 ◽  
Author(s):  
Sabrina Regalla ◽  
Bianca Pinheiro ◽  
Ilson Pasqualino ◽  
Luiz Daniel Lana ◽  
Valber Perrut
Keyword(s):  
Stress Concentration ◽  
Internal Pressure ◽  
Epoxy Matrix ◽  
Glass Fibers ◽  
Before And After ◽  
Repair Procedure ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors ◽  
Fatigue Life Enhancement

The aim of this work is to evaluate the residual fatigue life enhancement of damaged pipelines after the execution of composite material repairs made of laminates of epoxy matrix reinforced with glass fibers. In view of structural performance and cost concerns, the more suitable repair thickness should be proposed. The work comprises a numerical and experimental study on the stress concentration of damaged pipes under internal pressure before and after repair. A numerical model is developed, based on the finite element method, to provide stress concentration factors of damaged pipes (plain dent defect), under cyclic internal pressure, before and after applying glass fiber and epoxy matrix laminate repairs with varying thicknesses. Small-scale steel pipe samples are submitted to denting and the resulting stress concentration in the damaged region is estimated under cyclic internal pressure, before and after repair execution. From correlation between numerical and experimental results, the finite element model is calibrated and validated. A parametric study is carried out to evaluate stress concentration factors of dented pipes repaired with varying laminate thickness. Stress concentration factors of dented pipes under internal pressure after repair can be used in a fatigue assessment methodology from correction of S-N curves. The effect of repair thickness on the reduction of stress concentration factors is evaluated in view of the residual fatigue life enhancement of damaged pipes, beside repair procedure costs. Based on results of the parametric study, recommendations about the repair procedure using laminates of epoxy matrix reinforced with glass fibers will be proposed, comprising indications of the more suitable repair thickness, as a function of pipe and damage dimensions, in view of fatigue performance and cost concerns.

The Influence of Corrosion Pits and Cold Expanded Fastener Holes on the Fatigue Life Aluminium 7075-T651

2014 ◽  
Vol 891-892 ◽  
pp. 87-92 ◽  
Author(s):  
Benjamin Withy ◽  
Stephen Campbell ◽  
Glenn Stephen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Air Force ◽  
Fatigue Tests ◽  
Expansion Process ◽  
Cold Expansion ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Corrosion Pits

The Royal New Zealand Air Force (RNZAF) utilised the split sleeve cold expansion process to increase the fatigue life of fastener holes in the wings of the C130 transport fleet. As part of the validation of the fatigue improvements offered by the process the Defence Technology Agency conducted a series of fatigue tests on cold expanded fastener holes in aluminium 7075-T651, including specimens with corrosion induced after the cold expansion process had been performed. This research conducted an analysis of fatigue crack origins and modelled the stress concentration factors generated as a result of the corrosion pits. These results were used to explain the differing fatigue life and s-n curves produced by corroded and non-corroded fatigue specimens and the location of crack initiation sites around corroded cold expanded fastener holes.

Stress Concentration Factors of Dented Pipelines

2006 ◽  
Author(s):  
Bianca de Carvalho Pinheiro ◽  
Ilson Paranhos Pasqualino ◽  
Se´rgio Barros da Cunha
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Numerical Model ◽  
Finite Element Model ◽  
Internal Pressure ◽  
Element Model ◽  
Small Strain ◽  
Small Scale ◽  
Concentration Factors ◽  
Stress Concentration Factors

A nonlinear finite element model was developed to assess stress concentration factors induced by plain dents on steel pipelines subjected to cyclic internal pressure. The numerical model comprised small strain plasticity and large rotations. Six small-scale experimental tests were carried out to determine the strain behavior of steel pipe models during denting simulation followed by the application of cyclic internal pressure. The finite element model developed was validated through a correlation between numerical and experimental results. A parametric study was accomplished, with the aid of the numerical model, to evaluate stress concentration factors as function of the pipe and dent geometries. Finally, an analytical formulation to estimate stress concentration factors of dented pipelines under internal pressure was proposed. These stress concentration factors can be used in a high cycle fatigue evaluation through S-N curves.

Numerical Investigation of Pressure-Cycling Induced Fatigue Failure of Wrinkled Energy Pipelines

2021 ◽  
pp. 1-38
Author(s):  
Navjot Singh ◽  
Sreekanta Das ◽  
Peter Song ◽  
Nader Yoosef-Ghodsi
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Internal Pressure ◽  
Fatigue Failure ◽  
Fatigue Loading ◽  
Element Model ◽  
Pressure Cycling ◽  
Concentration Factors ◽  
Fatigue Life Analysis ◽  
Stress Concentration Factors

Abstract Wrinkle defects can be complex pipeline deformities to assess and can present the potential to initiate a pipeline release incident as a result of fatigue failure due to pressure cycling, if not dealt with accordingly. Specifically, the stress distribution arising due to applied loads such as internal pressure can vary rapidly due to the complex shape along the wrinkle profile, which may introduce complexities in subsequent assessments such as fatigue life analysis. This paper presents a methodology using numerical simulation for evaluating stress concentration factors of wrinkle defects of varying geometries. A nonlinear finite element model is developed to evaluate stress concentration factors induced by wrinkle defects within steel pipelines subjected to internal pressure. Afterwards, data from full-scale laboratory tests for the wrinkled pipe specimens subjected to cyclic pressure fatigue loading is analyzed to evaluate stress concentration factors for comparable wrinkle profiles. Lastly, a comparison between the results of the stress concentration factors evaluated using finite element method and test data is provided, followed with a brief discussion of potential sources of discrepancies between results obtained from these methods.

A Multidimensional FEA Approach for Determination of Hot Spot Stresses in Offshore Jacket Structures

2021 ◽  
Author(s):  
Kris Hectors ◽  
Hasan Saeed ◽  
Wim De Waele
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Hot Spot ◽  
Wave Spectrum ◽  
Wave Direction ◽  
Tubular Joints ◽  
Jacket Structures ◽  
Concentration Factors ◽  
Stress Concentration Factors

Abstract A new fatigue lifetime assessment approach for offshore jacket structures is presented. It combines a previously developed numerical framework for automated determination of stress concentration factors in tubular joints and a multidimensional finite element modelling approach. The approach is explained based on a case study of an OC4 type offshore jacket. To determine the fatigue life, a directional wave spectrum is combined with the JONSWAP spectrum. The fatigue life of the jacket is assessed for two different sea states. Based on the fatigue analysis the most fatigue critical wave direction is identified. The hot spot stresses in one of the most critical joints are determined and compared to stresses obtained with the Efthymiou equations. The shortcomings of these equations are highlighted and it is shown how the numerical framework can be used to improve the current fatigue design philosophy for offshore jackets which relies on the Efthymiou equations for stress concentration factors in the welded tubular joints.

Stress Concentration Factors for Stud-Less Mooring Chain Links in Fairleads

2004 ◽  
Author(s):  
Pedro M. Vargas ◽  
Teh-Min Hsu ◽  
Wai Kong Lee
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fine Tuning ◽  
Mooring Line ◽  
Loop Current ◽  
Parametric Problem ◽  
Chain Link ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Mooring Chain

Mooring chains are critical components of off-shore installations. The fatigue assessment of these components often requires complex calculations to determine the loadings in the mooring chains. Traditionally the loadings can be converted into fatigue lives using S-N curves such as the DnV Posmoor curve, or the API RP2 SK curve. Deep water SPARs undergoing vortex-induced-motion (VIM) in loop current conditions may be subject to higher mean/cyclic loadings with considerably lower fatigue life estimates — compared with earlier installations in which fatigue life estimates were so large that fine tuning fatigue prediction methodologies was only of academic interest. In this case a more accurate evaluation of the fatigue performance of mooring chains is needed. In this study the stress concentration factors (SCFs) of a studless 5.25” (133mm) mooring chain were examined in a seven-pocket fairlead. The chain-fairlead system analyzed in this study had a very tight fit (i.e., was not designed for passing connector links), and the results of this study will, in general, not be applicable to other chain-fairlead combinations without additional study. The computed SCFs of the stud-less link interacting with the fairlead pocket were compared to the corresponding SCFs in a chain link away from the fairlead. The study shows that the maximum SCF ratio is 1.15, significantly less than the upper bound 2.5 value recommended by Det Norske Veritas in OS-E301 in lieu of detailed analyses. This has a significant impact, nearly an order of magnitude, on fatigue life prediction of the chain, justifying the analytical effort. The study also found that the SCF of the chain link in the fairlead is a function of the geometry of the chain and the fairlead. As a result some guidance is provided in this paper with respect to the implications of minimum SCFs on other link and fairlead geometries. This study combines computational efforts from NEL and ChevronTexaco in a two-pronged approach where: 1) NEL provided calculations addressing parametric variations of the chain link angles of the mooring line leaving the fairlead and the chain tension levels, and 2) ChevronTexaco validated simplified modelling assumptions done by NEL to make the parametric problem tractable.

Sign in / Sign up

Export Citation Format

Share Document