scholarly journals Analysis of fatigue test data of retrieved mooring chain links subject to pitting corrosion

2022 ◽  
Vol 81 ◽  
pp. 103119
Author(s):  
Jorge Mendoza ◽  
Per J. Haagensen ◽  
Jochen Köhler
2014 ◽  
Author(s):  
Emmanuel Fontaine ◽  
Jeremy Rosen ◽  
Andrew Potts ◽  
Kai-Tung Ma ◽  
Robert Melchers

Author(s):  
Gary H. Farrow ◽  
Andrew E. Potts ◽  
Andrew A. Kilner ◽  
Phillip P. Kurts ◽  
Simon Dimopoulos ◽  
...  

Abstract The first phase of the Chain FEARS (Finite Element Analysis of Residual Strength) Joint Industry Project (JIP) aimed to develop guidance for the determination of a rational discard criteria for mooring chains subject to severe pitting corrosion which, based on current code requirements, would otherwise require immediate removal and replacement. Critical to the ability to evaluate the residual fatigue life of a degraded chain, is to have an accurate estimate of the chain in its as-new condition, thereby providing a benchmark for any loss in fatigue life associated with severe corrosion or wear. A large collection of fatigue test data was collated for comparison and to establish underlying trends in as-new mooring chain fatigue response. A non-linear multi-axial Finite Element Analysis (FEA) fatigue assessment method was developed to correlate against available as-new chain link fatigue test data and underlying failure trends as part of the JIP achieving this critical requirement. It was established that the linear FEA fatigue method currently employed in the industry is too simplistic and does not correlate with the fatigue test data, whereas an alternative method of assessing fatigue based on FEA, developed with respect to the DNV B1 material curve, correlates well with the available physical fatigue test data. The FEA method uses a non-linear chain link FEA and multi-axial stress fatigue calculation method to determine an equivalent Stress Magnification Factor (SMF). This method achieves good correlation of predicted utilisations and associated cycles-to-failure with fatigue test data and in respect of critical locations with evidenced failure locations. The method of equivalent SMF calculation accounted for the significant effects on fatigue performance including proof load induced residual stress, mean stress levels and the increase in material fatigue endurance associated with increased steel UTS (i.e. increased offshore mooring chain grade). The analytical method developed in this study achieved a high degree of correlation with as-new chain fatigue test data, and should enable the accurate prediction of fatigue stresses around a link and in particular for irregular geometry associated with corrosion degraded chain links.


Author(s):  
Gary H. Farrow ◽  
Andrew E. Potts ◽  
Eric Jal ◽  
Nicholas D’Arcy Evans ◽  
Andrew A. Kilner

Abstract The first phase of the Chain FEARS (Finite Element Analysis of Residual Strength) Joint Industry Project (JIP) aimed to develop guidance for the determination of a rational discard criteria for mooring chains subject to severe pitting corrosion which, based on current code requirements, would otherwise require immediate removal and replacement. Critical to the ability to evaluate the residual fatigue life of a degraded chain, is to have an accurate estimate of the chain in its as-new condition, thereby providing a benchmark for any loss in fatigue life associated with severe corrosion or wear. A large collection of fatigue test data was collated for comparison and to establish underlying trends in as-new mooring chain fatigue response, and a non-linear multi-axial Finite Element Analysis (FEA) fatigue assessment method was developed to correlate against available as-new chain link fatigue test data and underlying failure trends [1,2] as part of the JIP achieving this critical requirement. This study sought through collation and review of available fatigue test data to: • Identify relationships between chain fatigue performance and the key input parameters of chain type, grade and environmental conditions. • Compare and validate the fatigue test data against the current Code formulations for chain fatigue endurance. • Determine chain nominal stress S-N fatigue endurance curves against which to validate a numerical model developed as part of the Chain FEARS JIP for the assessment of as-new chain link fatigue endurance. The collated fatigue data was separated into groups associated with offshore mooring chain type (i.e. stud and studless), grade (i.e. ORQ, R3, R4 and R5) and environmental conditions (i.e. free corrosion in seawater and in-air) for review. Good correlation occurred between the two standard deviation lower bound of the mean curves and current Code formulation design curves. The mean curves of the collated fatigue test data were considered representative of the overall fatigue performance of chain links and as such formed a good basis for subsequent development and the validation of an FEA model for the assessment of chain fatigue endurance [1,2].


Author(s):  
Jorge Mendoza ◽  
Jacopo Paglia ◽  
Jo Eidsvik ◽  
Jochen Köhler

Mooring systems that are used to secure position keeping of floating offshore oil and gas facilities are subject to deterioration processes, such as pitting corrosion and fatigue crack growth. Past investigations show that pitting corrosion has a significant effect on reducing the fatigue resistance of mooring chain links. In situ inspections are essential to monitor the development of the corrosion condition of the components of mooring systems and ensure sufficient structural safety. Unfortunately, offshore inspection campaigns require large financial commitments. As a consequence, inspecting all structural components is unfeasible. This article proposes to use value of information analysis to rank identified inspection alternatives. A Bayesian Network is proposed to model the statistical dependence of the corrosion deterioration among chain links at different locations of the mooring system. This is used to efficiently update the estimation of the corrosion condition of the complete mooring system given evidence from local observations and to reassess the structural reliability of the system. A case study is presented to illustrate the application of the framework.


Author(s):  
Mahesh Dissanayake ◽  
Tariq Pervez Sattar ◽  
Shehan Lowe ◽  
Ivan Pinson ◽  
Tat-hean Gan

Purpose Mooring chains used to stabilise offshore floating platforms are often subjected to harsh environmental conditions on a daily basis, i.e. high tidal waves, storms, etc. Therefore, the integrity assessment of chain links is vital, and regular inspection is mandatory for offshore structures. The development of chain climbing robots is still in its infancy due to the complicated climbing structure presented by mooring chains. The purpose of this paper is to establish an automated climbing technique for mooring chain inspection. Design/methodology/approach This paper presents a Cartesian legged tracked-wheel crawler robot developed for mooring chain inspection. The proposed robot addresses the misalignment condition of the mooring chains which is commonly evident in in situ conditions. Findings The mooring chain link misalignment is investigated mathematically and used as a design parameter for the proposed robot. The robot is validated with laboratory-based climbing experiments. Practical implications Chain breaking can lead to vessel drift and serious damage such as riser rupture, production shutdown and hydrocarbon release. Currently, structural health monitoring of chain links is conducted using either remotely operated vehicles which come at a high cost or by manual means which increase the danger to human operators. The robot can be used as a platform to convey equipment, i.e. tools for non-destructive testing/evaluation applications. Originality/value This study has upgraded a previously designed magnetic adhesion tracked-wheel mooring chain climbing robot to address the misalignment issues of operational mooring chains. As a result of this study, the idea of an orthogonally placed Cartesian legged-magnetic adhesion tracked wheel robotic platform which can eliminate concerns related to the misaligned mooring chain climbing has been established.


Author(s):  
Torbjo̸rn Lindemark ◽  
Inge Lotsberg ◽  
Joong-Kyoo Kang ◽  
Kwang-Seok Kim ◽  
Narve Oma

Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME), StatoilHydro and DNV established a common project to investigate the reason for the difference between calculated fatigue lives and the in-service experience and to assess the fatigue capacity of stiffener web connections subjected mainly to web frame shear stresses. The main objective of the work was to establish fatigue test data and perform numerical analysis of collar plate connections in order to provide improved confidence in analysis methodology for fatigue life assessment. Large scale fatigue tests of different types of connections were carried out to obtain fatigue test data of collar plate connections. Finite element analyses were carried out for comparison with fatigue test data and with measured stresses on the test model. Based on this work recommendations on fatigue design analysis of connections between stiffeners and web frames have been derived. The background for this is presented in this paper.


2017 ◽  
Vol 105 ◽  
pp. 128-143 ◽  
Author(s):  
Davide Leonetti ◽  
Johan Maljaars ◽  
H.H. (Bert) Snijder

Sign in / Sign up

Export Citation Format

Share Document