Flexible Riser Fatigue Evaluation for FPSO’s in Bi-Directional Sea Spectra

2003 ◽  
Author(s):  
Carlos Alberto Duarte de Lemos ◽  
Murilo Augusto Vaz ◽  
Marcos Queija de Siqueira
Keyword(s):  
Operational Experience ◽  
Flexible Riser ◽  
Mooring Lines ◽  
Directional Spectrum ◽  
Campos Basin ◽  
Calculation Methodology ◽  
Flexible Risers ◽  
Fatigue Evaluation ◽  
Simplified Procedure ◽  
The Impact

The fatigue calculation methodology applied to flexible risers connected to FPSOs, offshore Brazil, is based on a simplified procedure considering a deterministic regular wave approach and a wave heading distribution supported by past operational experience with semi-submersible platforms. However the utilization of deterministic waves approach does not necessarites guarantee the consideration of the worst sea conditions, and the weathervaning capability of those systems are usually not accounted for when non-collinear wave, wind and current are present. A new procedure is being evaluated considering an integrated model for ship, mooring lines and risers to define the distribution of ship headings for fatigue analysis using an irregular bi-directional sea approach. The impact on a flexible riser’s fatigue life will be evaluated when a new ship heading distribution with irregular bi-directional spectrum is presented for the case of a FPSO with bow turret in operation at the Marlin Field offshore Campos Basin.

Nonlinear Analysis of Flexible Risers Using Hybrid Finite Elements

1988 ◽  
Vol 110 (3) ◽  
pp. 197-204 ◽  
Author(s):  
J. F. McNamara ◽  
P. J. O’Brien ◽  
S. G. Gilroy
Keyword(s):  
Mixed Finite Element ◽  
Element Formulation ◽  
Wave Loading ◽  
Flexible Riser ◽  
Mooring Lines ◽  
Static And Dynamic Analysis ◽  
Hybrid Beam ◽  
Offshore Production ◽  
Flexible Risers ◽  
Finite Bending

A method is developed for the static and dynamic analysis of flexible risers and pipelines in the offshore environment under conditions of arbitrarily large motions due to wave loading and vessel movements. A mixed finite element formulation is adopted where the axial force is independently interpolated and only combined with the corresponding axial displacements via a Lagrangian constraint. An advantage of the resulting hybrid beam element is that it may be applied to offshore components varying from mooring lines or cables to pipelines with finite bending stiffnesses. Results are presented for the motions and forces on a flexible riser connecting a tanker to a subsea tower and also on a combined flexible riser and subsea support buoy structure which is part of a floating offshore production system.

Dynamic Flexible Riser Ancillary Equipment—North Sea Asset Integrity Management Experience and Lessons Learned

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Damir Tadjiev
Keyword(s):  
Case Studies ◽  
North Sea ◽  
Oil And Gas ◽  
Lessons Learned ◽  
Operational Experience ◽  
Flexible Riser ◽  
Remotely Operated Vehicle ◽  
Integrity Management ◽  
Flexible Risers ◽  
Ancillary Equipment

Abstract Dynamic flexible risers are complex engineered systems, which provide a connection between topside (normally floating) facilities and subsea pipeline infrastructure on offshore oilfields. Such systems require the use of ancillary equipment to ensure the riser’s correct configuration is maintained throughout the service life. Industry experience shows that the integrity management of riser ancillary equipment is not always comprehensive, and failure of such equipment is one of the causes of premature removal of flexible risers from service. This article presents some case studies from the operational experience of dynamic flexible risers by an operator in the UK North Sea covering a period of approximately 20 years. The case studies look at the anomalies identified in service by general visual inspection (GVI) using a remotely operated vehicle (ROV) and the lessons learned. Some of the anomalies, had they not been identified and addressed promptly, could have resulted in costly repairs, which demonstrates the importance of inspecting the ancillary equipment of flexible risers as a part of the riser integrity management strategy. The challenges associated with integrity management of ancillary equipment of dynamic flexible risers are also discussed. The case studies presented in this article demonstrate that ROV GVI is an effective method for identifying installation and in-service anomalies related to flexible riser ancillary equipment. The purpose of this article is to share lessons learned with the wider offshore oil and gas community. It is also believed that the information presented in this article may provide useful information to other users of dynamic flexible riser systems when developing and/or implementing their subsea pipelines integrity management programs.

Effect of Anti-Wear Tape on Behavior of Flexible Risers

2014 ◽  
Author(s):  
Chongyao Zhou ◽  
Naiquan Ye ◽  
Svein Sævik
Keyword(s):  
Numerical Analysis ◽  
Numerical Model ◽  
Cross Section ◽  
Bending Moment ◽  
Laboratory Measurements ◽  
Flexible Riser ◽  
Bending Loads ◽  
Flexible Risers ◽  
Bending Behavior ◽  
The Impact

The service life of a flexible riser is often dominated by the metallic layers under cyclic bending loads, particularly the tensile armor layers. The effect of the anti-wear tapes is normally omitted during cross section modelling, where a plane-remain-plane assumption is usually used for stick condition. Significant differences have been observed between numerical analysis assuming plane surfaces remain plane and laboratory measurements studying the bending moment versus curvature for a flexible riser which has anti-wear tapes between the two tensile armor layers. A new shear interaction algorithm has been developed in the numerical model to improve the modeling of the anti-wear tapes by taking the thickness and shear modulus of the anti-wear material into account. The impact of these parameters on the bending behavior of the flexible riser is demonstrated by comparing the numerical analysis results with the laboratory measurements.

Flexible Riser Fatigue Procedure Using a Long Term Distribution of FPSO’s Heading Direction

2002 ◽  
Author(s):  
Carlos Alberto Duarte de Lemos ◽  
Murilo Augusto Vaz
Keyword(s):  
Environmental Conditions ◽  
Environmental Data ◽  
Mooring Lines ◽  
Fatigue Design ◽  
Beam Seas ◽  
Heading Direction ◽  
Campos Basin ◽  
Directional Waves ◽  
Flexible Risers

The intensive use of FPSOs in Campos Basin, offshore Brazil, has demanded more attention on the fatigue design of flexible risers. Field experience and a new set of environmental data collected in the last years have shown a large number of swell waves reaching the floating units in quartering and beam seas, which has amplified the motions at the risers’ top connections. Hence, it is necessary to evaluate the occurrence probability of wave heading direction relative to the vessel, especially for beam seas, but also noting the probability increase of quartering seas considering the existence of bi-modal and bi-directional wave spectra. The simultaneous environmental conditions — wind, current and bi-directional waves (sea and swell) — registered in Campos Basin, were condensed in a few hundreds environmental conditions to enable its utilization on a simulation program, where the FPSO, mooring lines and risers were modeled to obtain the mean heading and offsets. This new set of FPSO headings were then used to define a new proposal of load conditions to evaluate the fatigue life of flexible risers. This new procedure was then applied to a case study for the FPSO P-33 employing the tools available at PETROBRAS research center. The results have confirmed the importance of beam and quarter seas, which respectively cause heavy roll and vertical motions at the turret and then, affecting the fatigue of the risers.

Methodology for Determining Remnant Fatigue Life of Flexible Risers Subjected to Slugging and Irregular Waves

2012 ◽  
Author(s):  
Paul Gundersen ◽  
Krassimir Doynov ◽  
Torgrim Andersen ◽  
Rune Haakonsen
Keyword(s):  
Time Series ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
International Standards ◽  
Irregular Waves ◽  
Operational Experience ◽  
Analysis Tool ◽  
Flexible Risers ◽  
Wave Induced ◽  
The Impact

Operational experience has shown that flexible risers producing different combinations of oil, gas and water can be subjected to increased dynamic motions due to slugging — a cyclic accumulation of finite volumes of liquids at a low point of the riser (e.g. sag point of a lazy-S riser) until sufficient pressure is built up behind the slug to push the liquids up through the riser. It has been observed that the slug induced dynamic riser motions can cause riser displacements larger than those generated by moderate and some extreme waves in the absence of slugging. A major impact of the slug induced riser motions is the increased fatigue damage of the tensile wires — the cross-sectional component that most frequently defines the fatigue resistance of flexible riser systems. While international standards like ISO 13628-2 & -11 require and recommend that the effects of slug flow on riser response are considered, they provide no guidance on how to practically incorporate potential slugging effects in pipe design or analysis. A methodology has been developed to determine the remnant fatigue life of a riser subjected to slug induced motions combined with the normally considered vessel motions and wave loading. The methodology is based on using commercially available global and local riser analysis tools. The global analysis tool is used to determine the riser response induced by continuous and regular slug loading combined with loading from different irregular waves, vessel offsets and motions. The slug loading parameters are determined through an iterative process calibrating riser displacements and frequencies with those observed in the field. The local analysis tool is used to determine wire stress transfer functions, which in turn are used to derive wire stress time series from the riser tension and curvature time histories. Stress ranges are identified through rain-flow counting applied on all the calculated stress time series and fatigue performance is estimated using the Palmgren Miner summation of damage using an appropriate wire S-N curve. In a case study, the combined slug and first order wave induced fatigue damage increased by a factor of approximately two compared to the wave induced damage alone. This methodology can be used for: a) riser fitness for service assessments by bounding the impact of slug-induced riser motions observed in the field, and b) new riser design when slugging parameters are adequately bounded by flow assurance calculations.

Riser Top Loads on Turret Moored FPSO

2009 ◽  
Author(s):  
Felipe de Arau´jo Castro ◽  
Carlos Magluta ◽  
Gilberto Bruno Ellwanger
Keyword(s):  
Production Systems ◽  
Wind Waves ◽  
Model Tests ◽  
Structural Damping ◽  
Mooring Lines ◽  
Load Variations ◽  
Campos Basin ◽  
Loading Case ◽  
Flexible Risers ◽  
Important Design

In the Campos Basin, offshore Brazil, catenary flexible risers are extensively used in marine production systems. One of the most important design phases of these systems is the riser extreme top load analysis, which provides results for riser and accessory designs as well as input for structural analysis of platform supports. In addition to the riser’s characteristics (weight, diameter, structural damping, axial and bending stiffness), riser top loads depend on several other factors, such as platform static and dynamic behavior, including the collective effect of lines (mooring lines and risers) drag and damping, platform motion, connection support position and environmental loading cases. This study is based on the results from a model test and numerical analysis of a typical turret moored FPSO system, with catenary risers and mooring lines. This test was programmed to evaluate the consequence of each of the above mentioned parameters on flexible riser top loads. Model tests were performed in the MARIM (Maritime research Institute Netherlands) wave tank to represent the offshore system in 850 meter water depth and included loading case tests combining wind, waves and current in different relative directions (collinear, crossed and transversal). The analysis of the model tests results indicated significant variations in the platform behavior, when the drag and damping generated by the risers and mooring lines were taken into account. Additional analyses were performed, based on numerical simulations of the top load variations (axial, shear tension and moment), induced by movement changes (added drag and damping caused by risers and mooring lines) and to evaluate the influence of vessel heading on top load results.

Safety Factors for Fatigue Analysis of Flexible Pipes Based on Structural Reliability

2012 ◽  
Author(s):  
Fernando dos Santos Loureiro Filho ◽  
Edison Castro Prates de Lima ◽  
Luís Volnei Sudati Sagrilo ◽  
Fernando Jorge Mendes de Sousa ◽  
Carlos Alberto Duarte de Lemos
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Fatigue Analysis ◽  
Design Criterion ◽  
Flexible Riser ◽  
Safety Factors ◽  
Common Procedure ◽  
Flexible Pipes ◽  
Campos Basin ◽  
Flexible Risers

Structural reliability–based methodology [1,2] has been proposed for fatigue analysis of flexible pipes tension armours. In this methodology a design criterion is verified using a standard reliability analysis approach and checking if the fatigue failure probability is equal to or less than a target value. The use of reliability analysis in the every day design practice is not yet a common procedure. Hence, in this paper we present the calibration of safety factors for Brazilian environmental conditions to be used in the standard fatigue analysis of flexible riser tension armours. The calibration is performed in order to guarantee the same target probability of failure. The safety factors are calibrated considering four flexible risers, two connected to FPSOs and the other two to semi-submersibles located in different water depths in Campos Basin offshore Brazil.

USING FIELD DATA FOR THE EVALUATION OF THE IMPACT OF ULTRA-LOW FREQUENCY MOTIONS ON THE FATIGUE OF MOORING LINES

2019 ◽  
Author(s):  
Guilherme Borzacchiello ◽  
Carl Albrecht ◽  
Fabricio N Correa ◽  
Breno Jacob ◽  
Guilherme da Silva Leal
Keyword(s):  
Field Data ◽  
Low Frequency ◽  
Mooring Lines ◽  
The Impact

Static grid carbon factors – Can we do better?

2021 ◽  
pp. 014362442199196
Author(s):  
Jamie Risner ◽  
Anna Sutherland
Keyword(s):  
Carbon Emissions ◽  
Regional Analysis ◽  
Electricity Consumption ◽  
Carbon Intensity ◽  
External Temperature ◽  
Building Regulations ◽  
Calculation Methodology ◽  
Alternative Methodology ◽  
The Uk ◽  
The Impact

The average carbon intensity (gCO2e/kWh) of electricity provided by the UK National Grid is decreasing and becoming more time variable. This paper reviews the impact on energy calculations of using various levels of data resolution (half hourly, daily, monthly and annual) and of moving to region specific data. This analysis is in two parts, one focused on the potential impact on Part L assessments and the other on reported carbon emissions for existing buildings. Analysis demonstrated that an increase in calculated emissions of up to 12% is possible when using an emissions calculation methodology employing higher resolution grid carbon intensity data. Regional analysis indicated an even larger calculation discrepancy, with some regions annual emissions increasing by a factor of ten as compared to other regions. This paper proposes a path forward for the industry to improve the accuracy of analysis by using better data sources. The proposed change in calculation methodology is analogous to moving from using an annual average external temperature to using a CIBSE weather profile for a specific city or using a future weather file. Practical application: This paper aims to quantify the inaccuracy of a calculation methodology in common use in the industry and key to building regulations (specifically Building Regulations Part L – Conservation of Fuel and Power) – translating electricity consumption into carbon emissions. It proposes an alternative methodology which improves the accuracy of the calculation based on improved data inputs.

Cathodic Protection Design Consideration for an Offshore Flexible Riser Connected to an Impressed Current System

2021 ◽  
Author(s):  
Thierry Dequin ◽  
Clark Weldon ◽  
Matthew Hense
Keyword(s):  
Cathodic Protection ◽  
Sacrificial Anode ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Linear Resistance ◽  
Flexible Pipes ◽  
Flexible Risers ◽  
Impressed Current ◽  
Host Structure ◽  
Impressed Current Cathodic Protection

Abstract Flexible risers are regularly used to produce oil and gas in subsea production systems and by nature interconnect the subsea production system to the floating or fixed host facilities. Unbonded flexible pipes are made of a combination of metallic and non-metallic layers, each layer being individually terminated at each extremity by complex end fittings. Mostly submerged in seawater, the metallic parts require careful material selection and cathodic protection (CP) to survive the expected service life. Design engineers must determine whether the flexible pipe risers should be electrically connected to the host in order to receive cathodic protection current or be electrically isolated. If the host structure is equipped with a sacrificial anode system, then electrical continuity between the riser and the host structure is generally preferred. The exception is often when the riser and host structure are operated by separate organizations, in which case electrical isolation may be preferred simply to provide delineation of ownership between the two CP systems. The paper discusses these interface issues between hull and subsea where the hull is equipped with an impressed current cathodic protection (ICCP) system, and provides guidance for addressing them during flexible pipe CP design, operation, and monitoring. Specifically, CP design philosophies for flexible risers will be addressed with respect to manufacturing, installation and interface with the host structure’s Impressed Current Cathodic Protection (ICCP) system. The discussion will emphasize the importance of early coordination between the host structure ICCP system designers and the subsea SACP system designers, and will include recommendations for CP system computer modeling, CP system design operation and CP system monitoring. One of the challenges is to understand what to consider for the exposed surfaces in the flexible pipes and its multiple layers, and also the evaluation of the linear resistance of each riser segment. The linear resistance of the riser is a major determinant with respect to potential attenuation, which in turn largely determines the extent of current drain between the subsea sacrificial anode system and the hull ICCP system. To model the flexible riser CP system behavior for self-protection, linear resistance may be maximized, however the use of a realistic linear resistance is recommended for evaluation of the interaction between the host structure and subsea system. Realistic flexible linear resistance would also reduce conservatism in the CP design, potentially save time during the offshore campaign by reducing anode quantities, and also providing correct evaluation of drain current and stray currents.

Sign in / Sign up

Export Citation Format

Share Document