As a key driver of degradation in mooring chains, the phenomenon of wear is particularly important to the offshore floating production sector. Severe wear in the vicinity of the fairlead has been implicated in the loss of mooring lines.
While significant wear is already being observed in short term moorings, as operators look for more value from their fields, extending service life beyond 15 years, wear can become the governing factor of mooring system degradation.
Existing Guidance
The current level of codification regarding wear on anchor chains is rudimentary. Current practice allows for an average annual loss of chain due to the combined effects of corrosion and wear.
- Implicit wear allowance in design codes: 0 to 0.6 mm/year.
- Predicted wear rates from preliminary full-scale lab tests: 0.6 - 1.8 mm/year.
Over the lifetime of long term mooring systems, costly intervention actions may be required to counter higher than anticipated wear rates.
State of Knowledge
- No validated analytical model exists to accurately predict wear in varying conditions.
- Some models work well within a specific range of conditions, but are not practically applicable for predicting wear in mooring lines under realistic loading conditions.
- Preliminary chain wear experiments, undertaken in the SCORCH JIP, provided useful insights into the process of mooring chain wear.
- Further testing of chain required under a range of conditions is required to provide a practical and robust framework for the prediction of wear
Proposal
It is proposed that a Chain Wear JIP be established to develop a more robust methodology for predicting wear which will enable JIP participants to:
- Reduce operational costs through the minimization of costly unplanned mooring repairs
- Increase the level of safety and reliability of their systems
The broad objectives of the JIP are to:
- Derive a proven methodology to assess chain wear as a function of various external factors (load duty, interlink motion, chain grade, chain size, etc.)
- Build models for predicting wear allowances under a broader spectrum of practical in-service parameters
- Issue guidance for predicting wear allowances
The Chain Wear JIP will be of direct relevance to:
- Offshore oil and gas companies
- Floating production and storage facility operators
- Floating facility designers
- Classification societies
- Safety regulatory authorities
- Chain manufacturers
Work Breakdown Structure
- Test Matrix Development
- Test System Selection
- Analysis of Typical Mooring Configurations
- Wear Test Matrix Specification
- Wear Tests
- Large Scale Wear Tests
- Small Scale Wear Tests
- Extended Test Programs
- Design Guidelines
- Design Wear Model Characterisation
- Application to Typical Mooring Configurations
- Benchmark Against Field Recovered Chains
- Class Society Independent Review
- Class Guidance Note
AMOG Capability For The JIP Management Role
Proven Track Record in Mooring Integrity and JIP delivery
- DeepStar Mooring Integrity Management development of model code and guidelines
- SCORCH JIP - development of predictive models and design guidance for the uniform and pitting corrosion of steel mooring chains and wire rope mooring lines
- Currently managing CHAIN FEARS JIP (Finite Element Analysis of Residual Strength) to develop predictive models and guidance for assessing residual strength and fatigue of heavily degraded mooring chains addressing MIC pitting corrosion and wear
- Application of Mooring Integrity Management philosophy to existing FPSO moorings
- Mooring system criticality assessments and detailed inspection plan development
- Inspection report review and interpretation and inspection strategy work plan development based upon inspection findings
- Planning, design analysis and execution support (including attendance) for emergency repairs and remediation of degraded mooring systems
- Mooring system emergency response planning assessments
For further information, contact:
Mr. Kanishka Jayasinghe
Phone: +61 3 9542 3700