Fatigue analysis of a steel catenary riser at touchdown zone with seabed resistance and hydrodynamic forces

Abstract This work presents methods for reducing computational costs to estimate fatigue damage in riser structures by simplifying the sea state matrix to be solved in time domain by finite element analyses. Two different methods are proposed: The Equivalent Damage Method (EDM), which is a lump block method with an innovative formulation using vessel linearized response to determine significant sea states; and the Response Surface Method (RSM), which uses results from a few sea states to estimate results for other intermediary scenarios required for the fatigue analysis. Basic assumptions and guidance on how to apply the proposed methods are explained through the text. The methods are used to solve an example of a Steel Catenary Riser (SCR) connected to a Semi-Submersible vessel, resulting in a reduction of almost 80% of the required computing time. Results show accurate values for damage estimates at the top of the riser, and limitations at the touch down zone. Advantages and disadvantages of each method are discussed in detail, demonstrating that they can be used with discretion at early design stages to estimate fatigue damage of risers, umbilicals and mooring lines in general.

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Fatigue Analysis of a Steel Catenary Riser With Uncertain Seabed Parameters

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2011-49880 ◽

2011 ◽

Author(s):

Feng Zi Li ◽

Ying Min Low

Keyword(s):

Random Variables ◽

Fatigue Analysis ◽

Soil Stiffness ◽

Steel Catenary Riser ◽

Surface Method ◽

Reliability Method ◽

Bending Stresses ◽

Steel Catenary Risers ◽

Touchdown Point ◽

Direct Numerical Integration

Steel Catenary Risers (SCRs) are commonly employed in deepwater oilfields. The most problematic aspect of fatigue analysis is the touchdown point, in which the dynamic bending stresses are highest and the uncertainties are most pronounced. From a previous study conducted by the authors, it is found that the fatigue damage is extremely sensitive to several seabed parameters. Thus the uncertainties in the seabed parameters should be properly accounted in order to achieve a reliable and economical SCR design. In this work, reliability analysis is performed with three seabed random variables, namely soil stiffness, soil suction, and seabed trench. The efficient First Order Reliability Method (FORM) is employed in conjunction with the Response Surface Method to yield the probability of fatigue failure. The results are then compared with direct numerical integration. Further, the dependency between the different random variables is investigated.

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A Frequency Domain Approach for Random Fatigue Analysis of Steel Catenary Risers at Brazil’s Deep Waters

23rd International Conference on Offshore Mechanics and Arctic Engineering, Volume 1, Parts A and B ◽

10.1115/omae2004-51104 ◽

2004 ◽

Cited By ~ 1

Author(s):

Claudio Marcio Silva Dantas ◽

Marcos Queija de Siqueira ◽

Gilberto Bruno Ellwanger ◽

Ana Lu´cia F. Lima Torres ◽

Marcio Martins Mourelle

Keyword(s):

Frequency Domain ◽

Fatigue Damage ◽

Time Domain ◽

Oil And Gas ◽

Large Diameter ◽

Water Injection ◽

Domain Analysis ◽

Frequency Domain Analysis ◽

Fatigue Analysis ◽

Steel Catenary Riser

The steel catenary riser was adopted by Petrobras as a cost-effective alternative for oil and gas export and for water injection lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. The installation of the P-18 SCR was a pioneer project of a free-hanging steel catenary riser linked to a semi-submersible [1] and demonstrated the technical feasibility of the concept. Fatigue damage verification is an important issue in SCR design, demanding a high number of loading cases to be analyzed. The random time domain nonlinear analysis is considered an attractive and reliable tool for fatigue analysis as nonlinearities are properly modeled and the random behaviour of environmental loadings is considered. As time domain analysis is high computer time consuming, the frequency domain analysis has been considered as an alternative tool for the initial phases of riser design to be used mainly for fatigue damage verification. This paper presents a methodology developed to perform a linearized frequency domain analysis aiming at fatigue damage verification. Two drilling risers were analyzed with the frequency domain procedure developed. The model of a steel lazy-wave riser was analyzed both in frequency and time domain in order to compare fatigue damage results. The analyses were performed using the Petrobras’s in-house computer codes ANFLEX, ALFREQ and POSFAL developed and implemented as part of projects from CENPES/PETROBRAS with “COPPE/UFRJ -The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”.

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Global and local fatigue analysis of X100 and X60 steel catenary riser girth welds

Journal of Structural Integrity and Maintenance ◽

10.1080/24705314.2017.1354155 ◽

2017 ◽

Vol 2 (3) ◽

pp. 181-189 ◽

Cited By ~ 1

Author(s):

Ronan J. Devaney ◽

Padraic E. O’Donoghue ◽

Sean B. Leen

Keyword(s):

Fatigue Analysis ◽

Steel Catenary Riser ◽

Girth Welds ◽

Global And Local

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Dynamic Response Simulation of SCR in TDZ Considering the Soil Property

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.226-228.1377 ◽

2012 ◽

Vol 226-228 ◽

pp. 1377-1381

Author(s):

Gan Li ◽

Xiao Ping Huang

Keyword(s):

Dynamic Response ◽

Soil Properties ◽

Hot Spot ◽

Bending Moment ◽

Critical Issue ◽

Fatigue Analysis ◽

Stress Variation ◽

Steel Catenary Riser ◽

Touchdown Point ◽

Interaction Problem

The pipe-soil interaction problem is a critical issue in the fatigue analysis of SCR. In this paper, investigation on the initial trench configuration in the touchdown zone (TDZ) of the steel catenary riser (SCR) and factors, which have influence on the trench configuration, such as the amplitude of top end motion were performed firstly. Then the bending moment variation at different points along the trench during the pull up and lay down, the trenches and dynamic response at the touchdown point (TDP) under different soil properties were also investigated. It should be noted that the pipe around the TDZ especially at the TDP, which bears the most drastic bending moment variation and stress variation, is the hot spot in the fatigue analysis of SCR, and the soil properties have big influence on the dynamic stress response amplitude.

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Fatigue Analysis Technique of Deepwater Steel Catenary Risers

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 5, Parts A and B ◽

10.1115/omae2010-20832 ◽

2010 ◽

Cited By ~ 2

Author(s):

Jing Cao

Keyword(s):

Vertical Motion ◽

Fatigue Analysis ◽

Design Criterion ◽

Steel Catenary Riser ◽

Start Up ◽

Analysis Technique ◽

Induced Motion ◽

Steel Catenary Risers ◽

Stress Concentration Factors ◽

Sour Service

With the advances in deepwater offshore industries, Steel Catenary Riser (SCR) offers advantages over others and has been widely deployed worldwide including Gulf of Mexico (GoM), West of Africa (WoA), and Offshore Brazil. SCR concept has been applied to all types of deepwater floaters. Among analyses and design criteria, fatigue is still the number one governing design criterion of the deepwater SCR regardless the floater types (SPAR, TLP, SEMI, and FPSO). Typical SCR fatigue analyses include first order and second order floater motion induced fatigue; vortex induced vibration (VIV), deep draft floater vortex induced motion (VIM) fatigue, floater vertical motion induced VIV, slugging fatigue, start-up and shut-down, installation, and other kinds of dynamic loading imposed to the SCR. This paper presents the state-of-art fatigue analysis requirement and technique of different kinds of fatigue analysis for deepwater SCRs. Detailed discussion is given to different kinds of fatigue damage of SCRs. Focus of fatigue analysis of each type of deepwater floater is pointed out. Detailed discussion is also given to the selection of SN curves, stress concentration factors, influence of sweet and sour service, and post-processing of fatigue sensitive welds. Several examples of SCR fatigue analysis are given to demonstrate the analysis techniques and practices.

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