Setting the Stage for a Novel Mooring Chain Integrity and Design Assessment Practice: The Partial SCF and Hot-Spot S-N Curve Approach

Abstract Mooring chain's integrity is vital for offshore floating production units since their function ensures the required station keeping ability of the unit and protects the unit and associated critical assets such as risers. The decision of when to keep or replace a corroded chain is important for operators in the offshore oil and gas industry. While this topic has been a subject of several studies, actual fatigue consumption of a mooring chain due to corrosion, in-service loads and predicting the remaining fatigue life of the same chain in permanent floating structures remains a challenge. Incidents of premature mooring line failure has raised concerns on validity of mooring chain reliability in Industry Standards. This paper investigates the probability of failure of mooring chains based on available failure statistics, and its implication on current design and life extension practice. A partial SCF approach is proposed to assess fatigue life of corroded mooring chains. The approach was developed and validated through Fatigue of Corroded Chains (FoCCs) Joint Industry Project (JIP). In addition to the FoCC JIP validation, this paper presents application of the proposed approach on two recent corroded chain fatigue tests to predict its cycles to failure without FEA assessments.