Fatigue Tests on Corroded Mooring Chains Retrieved From Various Fields in Offshore West Africa and the North Sea

Abstract When an aged mooring system seeks a life extension, it is necessary to assess the remaining fatigue life of the corroded mooring chain. This paper summarizes the results of fatigue tests performed on mooring chain samples retrieved from six different fields in West Africa and North Sea. The impacts of corrosion on fatigue life on the samples were researched. The tests were managed under a Joint Development Project, “Fatigue of Corroded Chains (FoCCs JDP)”. The objectives of the JDP are (1) to derive a methodology for assessing the remaining fatigue life of corroded chain, (2) to develop guidance for performing reliable FEA of chain links to assess remaining fatigue life, and (3) to provide more rational basis to improve industry guidance on mooring line replacement criteria for life extension. Fatigue test procedure was defined by the fifteen (15) participating members. The procedure specified the testing parameters, including mean tension, tension range, and test frequency. Six sets of fatigue tests have been completed in seawater with the number of cycles to failure recorded. These chain samples were retrieved from floating production and storage units, e.g. FPSOs and FSUs, that were still in service. Fatigue data obtained from the tests were plotted against the design SN curves and results from fatigue testing of new chain. It was found that most of these samples have limited amount of fatigue capacity remained. Most interesting finding is that the sharpness of the surface feature on the corroded chain link has a significant impact on the remaining fatigue life. Another interesting finding is that the surface feature created by corrosion can be quite distinct and unique depending on the geophysical locations where the sample came from. These findings and test results may serve as references for life extension assessment of an aged mooring system.

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Fatigue Assessment of “Corroded” Mooring Chain

Volume 3: Structures, Safety, and Reliability ◽

10.1115/omae2019-96191 ◽

2019 ◽

Author(s):

David A. Baker ◽

Zhen Li ◽

Sue Wang ◽

Xiying Zhang ◽

Yunliang Shao ◽

...

Keyword(s):

Finite Element ◽

Fatigue Life ◽

Fatigue Test ◽

Best Practice ◽

Fatigue Testing ◽

Fatigue Tests ◽

Element Analysis ◽

Cycle Count ◽

Remaining Fatigue Life ◽

Mooring Chain

Abstract Assessment of corroded mooring chain for continued service is a challenging task faced by industry. Current best practice relies heavily on qualitative inspection information collected during inspection campaign. There has been little investigation into this practice and whether it is an appropriate technique or can be improved. To address this issue, the Fatigue of Corroded Mooring Chains (FoCCs) Joint Industry Project (JIP), initiated in 2016 with fifteen (15) participating organizations, including oil majors, chain manufactures, consulting firms, and classification societies, to examine assessment methods for evaluating remaining fatigue life. JIP teams were formed to progress fatigue testing and finite element objectives. One such team, comprised of ExxonMobil, ABS and Asian Star Anchor Chain, has performed an additional series of fatigue tests beyond the core JIP work effort. A fatigue test was conducted to 1) demonstrate the utility of finite element analysis in the assessment of fatigue life and 2) demonstrate performance of simulated damage. This unique fatigue test program was conducted on mooring chain with manufactured “corrosion pits” of different dimensions. All chain surface features were digitally recorded and converted into finite element models. These models were subsequently analyzed to compare with test results — both cycle count and failure location. This paper presents the findings from these fatigue tests and finite element analyses and how they can be utilized for assessment of remaining fatigue life.

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Applying Digital Technologies Beyond Design Life

10.2118/207776-ms ◽

2021 ◽

Author(s):

Luiz Paulo Feijo ◽

Suqin Wang ◽

Christiane Machado

Keyword(s):

Fatigue Life ◽

Service Life ◽

Digital Technology ◽

Predictive Analytics ◽

Life Extension ◽

Structural Behaviour ◽

Structural Evaluation ◽

Design Service Life ◽

Remaining Fatigue Life ◽

Extension Process

Abstract This paper focuses on Floating Production Installations, which are assets designed based on site-specific environmental conditions to determine their design service life. The longevity of these assets depends on the fatigue aspects related to the structural elements and mooring systems. Among the challenges involving the continued services of ageing assets is the integrity of these elements. When an asset reaches its end of design service life, Operators often decide to undergo a life extension process for safe continued operations. Alife extension process generally includes three phases: investigation, determination and implementation. Following a baseline inspection to determine the present conditions of the structures, engineering assessments are to be carried out to evaluate the fatigue damage through the lifecycle of the installation and therefore determine the remaining fatigue life. Collecting information to execute these assessments is challenging and can be automated with the use of digital technology. Digital tools allow an accurate collection of data, providing a continuous evaluation of the remaining fatigue life and supporting an informed decision-making process. Observing the operation of several aging assets and their structural behaviour, the parameters to be measured during the installation's lifecycle have been identified along with other aspects that also contribute to the determination of its continued service. The recommended data acquisition for relevant measurements is summarized in this paper. The application of sensors and monitoring systems on the installations allows measuring these parameters on a continuous basis, and consequently, Operators are able to determine the degradation pattern that the structure is subject to. An estimation of the remaining fatigue life can be achieved by using predictive analysis, which, along with insights of the future expected corrosion, provides Operators the necessary basis to implement corrective measures and mitigations to avoid the occurrence of a failure. This paper offers an innovative, forward-looking technology that allies physics-based processes with digital technology, supported by predictive analytics and continuous structural evaluation, to assess the integrity of an offshore asset in support of safe continued services.

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Specimen Size Effect on Fatigue Properties of Surface-Micromachined Al-3%Ti Thin Films

First International Conference on Integration and Commercialization of Micro and Nanosystems, Parts A and B ◽

10.1115/mnc2007-21280 ◽

2007 ◽

Cited By ~ 1

Author(s):

Jun-Hyub Park ◽

Man Sik Myung ◽

Yun-Jae Kim

Keyword(s):

Thin Film ◽

Fatigue Life ◽

Fatigue Strength ◽

Evaluation Method ◽

High Cycle Fatigue ◽

Test Procedure ◽

Fatigue Tests ◽

Test Method ◽

Fatigue Properties ◽

Cycle Fatigue

This paper presents high cycle fatigue properties of an Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone and also describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film developed by authors. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile and fatigue tests were performed to obtain mechanical and fatigue properties. The specimen was made with dimensions of 1000μm long, 1.0μm thickness, and 3 kinds of width, 50, 100 and 150μm. High cycle fatigue tests for each width were also performed, from which the fatigue strength coefficient and the fatigue strength exponent were found to be 193MPa and −0.02319 for 50μm, 181MPa and −0.02001 for 100μm, and 164MPa and −0.01322 for 150μm, respectively. We found that the narrower specimen is, the longer fatigue life of Al-3%Ti is and the wider specimen is, the more susceptible to stress level fatigue life of Al-3%Ti was.

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Environmental Assisted Cracking of High Strength Subsea Material due to CP

Volume 4: Materials Technology ◽

10.1115/omae2019-96685 ◽

2019 ◽

Author(s):

Agnes Marie Horn ◽

Erling Østby ◽

Viggo Røneid ◽

Finn Kirkemo

Keyword(s):

Fatigue Life ◽

North Sea ◽

Fatigue Testing ◽

Research Work ◽

Design Guidelines ◽

Life Extension ◽

External Loading ◽

Test Program ◽

The North ◽

The North Sea

Abstract Several of the offshore fields in the North Sea are approaching the end of their design life and a cost-effective solution to maximize production is to document that life extension is feasible for an asset. A trend the resent years [1] is that the BOP become larger, hence the required fatigue life increases. One way to meet the increased fatigue life and external loading is to use higher strength steel to meet the design requirements set by the operators. This has motivated research related to the fatigue performance of the base material connector material both for air and under sea water with cathodic protection (CP) [2,3,4] and possible degradation of ductility and toughness in seawater with CP. However, relevant test data for wellheads material that have been in service is not to the authors knowledge, available, nor recommendations in design guidelines related to possible material degradation to be safely applied for life extension of these assets. To better evaluate life extension of subsea wellheads, a test campaign was initiated by Equinor on a retrieved wellhead in 2015. The wellhead had been in operation since 2000 in the North Sea. The general purpose of the test program was to evaluate if the low alloy steel AISI 8630 modified material had been substantial degraded during 15 years in service compared to design material properties and the materials susceptibility to hydrogen embrittlement. The test program performed consisted of slow strain rate testing (SSRT) to document possible reduction of strength and ductility, CTOD testing to document possible reduction in toughness and S-N testing to establish the fatigue strength reduction due to seawater with CP. The outline of the paper is as follows: first a summary of the latest research and trends within wellhead fatigue and materials are discussed. Next, a detailed description of the test program is given: SSRT, toughness testing and fatigue testing are presented. Finally, recommendations and proposal for further research work are given.

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Hysteresis, Temperature and Resistance Measurements for the Characterization of the Cyclic Deformation Behavior of Metals

Materials Science Forum ◽

10.4028/www.scientific.net/msf.567-568.51 ◽

2007 ◽

Vol 567-568 ◽

pp. 51-56

Author(s):

F. Walther ◽

Dietmar Eifler

Keyword(s):

Fatigue Life ◽

Electrical Resistance ◽

Cyclic Deformation ◽

Defect Density ◽

Fatigue Behavior ◽

Test Procedure ◽

Fatigue Tests ◽

Single Step ◽

Random Loading

Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed for the microstructure-related characterization of the fatigue behavior and for the fatigue life calculation of metals. The proceeding fatigue damage was evaluated using the change of the load-free electrical resistance, which is strongly influenced by the defect density of the individual material state. A new test procedure was applied for the fatigue assessment under random loading on the basis of cyclic deformation curves, similar to single step loading. A physically based fatigue life calculation “PHYBAL” was developed, which requires only three fatigue tests for the rapid and nevertheless precise calculation of S-N (Woehler) and fatigue life curves.

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World First Fatigue S-N Curve for Bonded Reinforcements for FPSO Application

Volume 4: Materials Technology ◽

10.1115/omae2019-96239 ◽

2019 ◽

Author(s):

Hamza Abbad El Andaloussi ◽

Luc Mouton ◽

Firas Sayed Ahmad ◽

Stéphanie Mahérault-Mougin ◽

Stéphane Paboeuf ◽

...

Keyword(s):

Fatigue Life ◽

Fatigue Behavior ◽

Construction Material ◽

Industrial Applications ◽

Fatigue Tests ◽

International Standards ◽

Life Assessment ◽

Life Extension ◽

No Production ◽

Being There

Abstract Steel is the most common construction material in the Oil & Gas industry, and it begins to rust the day it is cast. This observation raises several challenges for the asset integrity and life extension of all offshore units. Therefore, for the ageing FPSOs (>10 years), frequent and costly structural maintenance operations in hazardous environment may be required to repair their hull. While a standard ship can go to dry-dock for “crop and renew” maintenance operations through standard hot works techniques, a permanently moored asset has to be maintained in situ. The challenge is to perform these offshore structural maintenance operations with no production disruption while maximizing safety even for the most stressed areas such as a mid-ship deck plating. COLDSHIELD, a co-development between COLD PAD, TOTAL and IFP Energies nouvelles, has been set up to meet this very challenge. This innovative alternative to “crop and renew” is covered by approval certificate from Class. COLDSHIELD stops the corrosion and restores hull structural strength. Two industrial applications have been performed so far. Among the steps to be taken to demonstrate that such repair can be considered as permanent, it was mandatory to characterize the fatigue behavior of this reinforcement solution. While the fatigue behavior of steel has been an important research topic since the early eighties of the last century, its understanding for bonded composite materials is still at its infancy. Indeed, for the time being there is — to our knowledge — no S-N curve for structural bonded reinforcements. Full scale coupon specimen fatigue tests of the structural bonded reinforcements were conducted by COLD PAD, third-partied by Bureau Veritas and in collaboration with two laboratories (private and public) in order to study the adhesive fatigue. A statistical analysis was performed according to international standards. The resulting S-N curve is fit for industrial fatigue design. It demonstrates a comfortable fatigue strength (S-N curve presenting a slope of 9). This paper presents the results of a fatigue life assessment campaign of COLDSHIELD including the experimental setup, the fatigue test results, and the numerical analyses. It details the reason why the design is compatible with a stress-based approach. It also explains the conclusions that can be derived in terms of fatigue life for a deck repair campaign.

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Estimation of Remaining Fatigue Life for Elbow Pipe Subjected to Cyclic Overload

Volume 9: Rudy Scavuzzo Student Paper Symposium and Competition ◽

10.1115/pvp2012-78205 ◽

2012 ◽

Author(s):

Hisanori Abe ◽

Kazuya Matsuo ◽

Koji Takahashi

Keyword(s):

Fatigue Life ◽

Low Cycle Fatigue ◽

Fatigue Tests ◽

Cycle Fatigue ◽

Displacement Control ◽

Cyclic Overload ◽

Cumulative Fatigue Damage ◽

Remaining Fatigue Life ◽

Total Usage ◽

Damage Rule

Low-cycle fatigue tests for STPT410 elbow pipes were conducted under displacement control with and without an internal pressure of 9 MPa. First, preliminary fatigue tests were conducted under constant displacements of ±15, ±20 and ±30 mm. Next, two-step fatigue tests were carried out in which the elbows were first subjected to cyclic displacements of ±30 or ±20 mm, which correspond to cyclic overload, and then subjected to a second displacement of ±20 or ±15 mm until a fatigue crack penetrated. The total usage factor was 0.8∼1.2. Thus, the remaining fatigue life of a given elbow pipe can be predicted by the cumulative fatigue damage rule.

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