Mooring Failures and What to Do about Them

Mooring ChainMooring failures are one of the most critical events in offshore asset integrity. Between 2001-2011, there were 23 mooring failures detected on offshore assets. Fatigue and corrosion are the most frequent causes for failure. Failure and premature replacement are costly and force operators to ask questions, such as:

  • How can we avoid mooring line failure and premature mooring replacements?
  • How do we ensure we stay compliant throughout the life of the asset?
  • How should we manage the mooring system so that it’s still compliant if we want to extend the life of the asset?
  • Should we increase the frequency of inspection?

To answer these questions, maintain production from existing facilities, and manage new developments more efficiently, operators need to develop a Mooring Integrity Management Plan. An MIM plan means that the operators:

  • Know the present & future status of their assets through inspections and monitoring:
    • Regular inspections show weakened / damaged mooring components
    • Analytical modeling helps identify and evaluate critical / high risk components
    • Life expectancy of the asset can be estimated, based on the actual condition (measurements), degradation rates (inspection records), known metocean conditions, anticipated loading conditions, and resulting and expected fatigue damage
  • Are prepared to take necessary actions to maintain production:
    • Develop mooring repair procedures for readily available or spot market installation vessels (e.g., Anchor Handler Vessels, Construction Support Vessels, etc.)
    • Identify long lead items, capable installation vessels, installation aid requirements, staging and mobilization locations, import and export restrictions, etc.
    • Procure, fabricate, store, and maintain spare mooring components needed to repair or replace failed moorings.
    • Perform preliminary installation analyses to identify critical aspects of offshore operations
  • Take action to document as-built / baseline inspection information and maintain, repair, and replace moorings:
    • Plan and allocate the right personnel to perform inspection, maintenance and repair work
    • Stage and mobilize inspection equipment and / or spare components for offshore operations
    • Implement the Mooring Repair Plan that is already in place if necessary
  • Provide evidence of good IM practices and data management to satisfy safety and insurance requirements for on-going production operations and earn life extension approval from regulatory bodies:
    • Provide baseline / as-built information and equipment certifications
    • Demonstrate a well-planned and documented inspection and maintenance plan
    • Provide results and findings from regular maintenance and inspection work
    • Estimate degradation rates (e.g., corrosion, abrasion, wear, etc.) based on base-line and regular inspection results
    • Identification of any critical / high-risk components that should be monitored or measured more frequently
    • Demonstrate preparedness for mooring system damage or failure

Mooring failures are not inevitable. A detailed mooring integrity management plan can help identify potential maintenance needs, make necessary inspection schedule recommendations, and enable an operators’ preparedness to ultimately reduce costs from any unforeseen circumstances.

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