Application of Actual In-Service Spectrum to SCR Girth Welds

Fatigue is normally the limiting design criterion for Steel Catenary Risers (SCRs) and it represents its major engineering challenge. As a consequence, design of this component generally trusts on a very good fatigue resistance. A common practice, widely adopted in oil recovery industry, is to certify that specific welding procedures have proper fatigue strength equal or better than the one adopted in design; such fatigue strength is commonly evaluated under constant amplitude loading. However, SCRs are subjected to complex loading spectrums which are characterized by a wide range of loading amplitudes induced by different sources that include the overall system response of the barge. Therefore, interest arises in verifying the component response to representative loading spectrums of the actual SCR in-service conditions and determining if actual riser components qualification, under constant amplitude loading, presents discrepancies with their resistance under in-service fatigue conditions. This situation has motivated full scale fatigue performance evaluation of SCR girth welds under constant and variable amplitude loading spectrums. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results were compared and the accuracy of Miner’s linear cumulative damage rule has been evaluated. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results have been compared and the accuracy of Miner’s linear cumulative damage rule [1] has been evaluated.

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Development of Fatigue Testing of Full-Scale Girth Welded Pipes Under Variable Amplitude Loading

10.1115/omae2011-49942 ◽

2011 ◽

Cited By ~ 2

Author(s):

Yan-Hui Zhang ◽

Stephen Maddox

Keyword(s):

Fatigue Limit ◽

Fatigue Damage ◽

Fatigue Testing ◽

Full Scale ◽

Cumulative Damage ◽

Constant Amplitude ◽

Variable Amplitude ◽

Testing Procedures ◽

Fatigue Design ◽

Damage Rule

In service the great majority of structures and components are subjected to stresses of variable amplitude (VA). The fatigue design of welded joints in such structures is based on fatigue data obtained under constant amplitude loading, used in conjunction with a cumulative damage rule to estimate the damage introduced by cycles of varying magnitude in the service stress history. There are two major concerns with fatigue design of deepwater steel catenary risers (SCRs): the validity of cumulative damage rule and the damaging effect of stresses below the constant amplitude fatigue limit (CAFL). It is known that SCRs can experience very high numbers of low stress cycles due to vortex induced vibration (VIV) with the result that the choice of method for accounting for the fatigue damage due to stresses below the constant amplitude fatigue limit can be highly significant in terms of the estimated fatigue life. These two fundamental issues have been addressed in a recent group sponsored project. By successfully establishing a loading spectrum representative of that experienced by risers and developing the testing procedures for VA loading using the resonance testing rigs, the fatigue performance of full-scale girth welded pipes under VA loading were investigated. These loading spectra had the same peak/maximum stress histograms but different minimum stresses. Many tests lasted over 108 cycles to investigate the fatigue damage of small stresses in these spectra. This paper describes the development of the method by which fatigue testing of full-scale girth welded pipes under VA loading had been successfully performed.

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In-Service Fatigue Performance of SCR Girth Welds Installed by Reeling

Volume 6: Materials Technology; Polar and Arctic Sciences and Technology; Petroleum Technology Symposium ◽

10.1115/omae2012-83465 ◽

2012 ◽

Author(s):

Philippe P. Darcis ◽

Eduardo Aguilar ◽

Emma Erezuma ◽

Israel Marines-Garcia ◽

Eduardo A. Ruiz ◽

...

Keyword(s):

Time History ◽

Cumulative Damage ◽

Fatigue Performance ◽

Variable Amplitude Loading ◽

Variable Amplitude ◽

Failure Initiation ◽

Service Conditions ◽

Girth Welds ◽

Damage Rule ◽

Loading Spectrum

Interest arises on verifying the SCR girth welds fatigue response to a more representative loading spectrum of the actual in-service conditions and after reel-lay deformation. It is important to determine if the actual riser component’s qualification, without pre-straining and under constant amplitude loading, evidences discrepancies with in-service conditions, in terms of fatigue strength. This situation has motivated the full scale S-N fatigue performance evaluation of SCR girth welds under constant and variable amplitude loading, and after reel-lay simulations. A CMn steel X65 pipe 10.75” outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure developed for girth welds manufacturing involved the use of the Lincoln STT® process for the root pass and the GMAW process for the fill and cap passes. Reeling trials were performed at Stress Engineering Services, Houston, U.S.A.. A dedicated commercial software was used to simulate the variable amplitude loading spectrum, which is representative of a SCR Touch Down Point (TDP) in West of Africa at a water depth of 1,200 m (3937 ft) and a FPSO as production platform. The experimental approach was focused on estimating the damage introduced by reeling and by loading cycles of various magnitudes in the riser service time history. Results of strained and unstrained specimens, tested at constant and variable amplitude, have been compared, and the cumulative damage rule typically used by Riser fatigue designers has been evaluated (i.e. Miner’s linear cumulative damage rule). Systematic fractographic investigations were performed on all the samples after testing to identify their fatigue failure initiation causes.

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Free-Span Flowlines Resistance to In-Service Fatigue Loading

Volume 5B: Pipeline and Riser Technology ◽

10.1115/omae2015-42034 ◽

2015 ◽

Author(s):

Francesco Iob ◽

Elisabetta Mecozzi ◽

Luigi Di Vito ◽

Philippe Darcis ◽

Israel Marines-Garcia ◽

...

Keyword(s):

Sensitivity Analysis ◽

Complex Loading ◽

Fatigue Loading ◽

Product Line ◽

System Response ◽

Reference Scenario ◽

Span Length ◽

Constant Amplitude ◽

Line Pipe ◽

Variable Amplitude

Offshore petroleum fields frequently pass over areas with uneven seafloor. In such cases the pipeline may have free spans due to depressions crossing and are subjected to complex loading spectra. A major source for dynamic stresses in free span pipelines is vortex induced vibrations (VIV) caused by steady current since wave induced velocities and accelerations will decay with increasing water depth. The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (line pipe and its girth welds). Centro Sviluppo Materiali and Tenaris for some years are involved in the study of in-service variable amplitude fatigue loading of risers trough numerical calculations and comparison of the actual fatigue loading experienced by free span system with constant amplitude qualification typical loading. Two papers [1, 2] have been already presented in previous OMAE conferences. The present work reports a study dedicated to the free-span flow lines. The flow line analyzed is composed by OD 273.05 mm × WT 25.4 mm pipe lying on the uneven seabed. In particular the attention is focused on the analysis of VIV and its effect on fatigue life of the line. The Ormen Lange field, located at 120 km northwest of the Mid-Norway, was selected as reference scenario for the study. One of the most important factors influencing the pipeline response to the VIV is the free-span length. A sensitivity analysis about the influence of different parameters (free span length and fluid velocity) on system response and consequent fatigue damage has been performed. A case study has been selected among the cases considered in the sensitivity analysis, to produce the loading spectra to be considered in a laboratory fatigue testing campaign on strip specimens. The fatigue performance of these samples has been compared to analogous samples subjected to constant and variable amplitude loading available from previous works [1, 2] on riser systems (Steel catenary riser and Hybrid riser).

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Cumulative Damage Under Constant Amplitude and Variable Amplitude Loading: Some New Physical Aspects

Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials ◽

10.1007/978-94-009-3459-7_7 ◽

1987 ◽

pp. 49-54 ◽

Cited By ~ 1

Author(s):

K. Middeldorf ◽

H. Nowack ◽

A. Fischer ◽

H. Harig

Keyword(s):

Cumulative Damage ◽

Constant Amplitude ◽

Variable Amplitude Loading ◽

Variable Amplitude

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Fatigue Characteristic of Designed T-Type Specimen under Two-Step Repeating Variable Amplitude Load with Low-Amplitude Load below the Fatigue Limit

Journal of Marine Science and Engineering ◽

10.3390/jmse9020107 ◽

2021 ◽

Vol 9 (2) ◽

pp. 107

Author(s):

Jin Gan ◽

Di Sun ◽

Hui Deng ◽

Zhou Wang ◽

Xiaoli Wang ◽

...

Keyword(s):

Stress Ratio ◽

Type Specimen ◽

Fatigue Tests ◽

Cumulative Damage ◽

Cyclic Loads ◽

Constant Amplitude ◽

Type Specimens ◽

Variable Amplitude ◽

Non Linear ◽

Low Amplitude

In order to investigate the non-linear fatigue cumulative damage of joints in ocean structural parts, one type of low carbon steel Q345D was employed to prepare designed T-type specimens, and a series of fatigue experiments were carried out on the specimens under two-step repeating variable amplitude loading condition. The chosen high cyclic loads were larger than the constant amplitude fatigue limit (CAFL) and the chosen low cyclic loads were below the CAFL. Firstly, the S-N curve of designed T-type specimen was obtained via different constant amplitude fatigue tests. Then, a series of two-step repeating variable load were carried out on designed T-type specimens with the aim of calculating the cumulative damage of specimen under the variable fatigue load. The discussions about non-linear fatigue cumulative damage of designed T-type specimens and the interaction effect between the high and low amplitude loadings on the fatigue life were carried out, and some meaningful conclusions were obtained according to the series of fatigue tests. The results show that fatigue cumulative damage of designed T-type specimens calculated based on Miner’s rule ranges from 0.513 to 1.756. Under the same cycle ratio, the cumulative damage increases with the increase of high cyclic stress, and at the same stress ratio, the cumulative damage increases linearly with the increase of cycle ratio. Based on the non-linear damage evaluation method, it is found that the load interaction effect between high and low stress loads exhibits different damage or strengthening effects with the change of stress ratio and cycle ratio.

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Hybrid Riser Resistance to In-Service Fatigue Loading

Volume 6B: Pipeline and Riser Technology ◽

10.1115/omae2014-24023 ◽

2014 ◽

Author(s):

Francesco Iob ◽

Elisabetta Mecozzi ◽

Luigi Di Vito ◽

Philippe Darcis ◽

Israel Marines-Garcia ◽

...

Keyword(s):

Cross Flow ◽

Complex Loading ◽

Fatigue Loading ◽

Fatigue Performance ◽

Variable Amplitude Loading ◽

Variable Amplitude ◽

Riser Pipe ◽

Wide Range ◽

Girth Welds ◽

Loading Spectrum

Riser systems are subjected to complex loading spectra. A wide range of amplitude loading are induced by naturally complex sea states. The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (riser pipe and its girth welds or threaded connections). The present paper reports numerical calculations and a comparison of the actual fatigue loading experienced by different riser systems, Steel Catenary Risers (SCR), Lazy Wave Riser (LWR), Hybrid Risers (HR). For the Hybrid riser system, a good fatigue resistance, due to the vessel and wave first motion decoupling, is obtained. On the other hand, the phenomenon of cross flow vibration induced by Vortex Induced Vibrations (VIV), could significantly affect the hybrid riser fatigue performance. In this case, a sensitivity analysis has been performed to evaluate the influence of different parameters, on the applied fatigue loading, like: riser tension, hydro diameter (i.e. external pipe diameter including coating), riser wall thickness, current velocity. The HR variable amplitude loading spectrum, derived from in-service conditions, referred to Gulf of Mexico scenario, has been calculated and applied in laboratory tests on girth welds of X65, 10.75″ OD, 25.4 mm WT riser. Furthermore, the fatigue performance of these tests has been compared to analogous tests on samples subjected to constant and variable amplitude loading available from previous work on SCR system[1].

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RC Beam Bridge’s Fatigue Cumulative Damage Rule Research

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.787.829 ◽

2013 ◽

Vol 787 ◽

pp. 829-832

Author(s):

Hong Bing Zhu ◽

Bo Xia ◽

Yao Zhao

Keyword(s):

Fatigue Damage ◽

Fatigue Tests ◽

Cumulative Damage ◽

Rc Beam ◽

Constant Amplitude ◽

Advantages And Disadvantages ◽

Damage Theory ◽

Theory Research ◽

Beam Bridge ◽

Damage Rule

Fatigue damage is the RC beam bridge is facing a big problem, for the RC beam bridge fatigue tests and fatigue cumulative damage theory research is very meaningful. Summarizes the research achievements of the RC beam bridge fatigue test, from constant amplitude fatigue, luffing fatigue and stochastic fatigue, etc, are discussed in this paper. Analyses the existing linear, nonlinear and probability fatigue cumulative damage theory and its applicable conditions, advantages and disadvantages. RC fatigue tests were discussed and the problems that exist in the fatigue cumulative damage theory research.

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