Risk-based corrosion assessment and refurbishment of marine structures

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This paper outlines a holistic, risk-based approach to managing the service life of existing liquefied natural gas (LNG) and liquefied petroleum gas (LPG) marine structures in Western Australia. The structures have been in service since 1989 (LNG) and 1995 (LPG) and are nearing the end of their original design life. The objective of this approach is to extend the design life for an additional 20 years to 2040. The risk-based assessment (RBA) process is composed of three main steps undertaken in sequence to identify and quantify refurbishment requirements for the timeframe. A two-campaign approach was considered, the first being in 2019 (Phase 1) and the second in 2030 (Phase 2). The RBA process combines innovative and conventional inspection techniques with a detailed desktop structural assessment of the remaining life of the structures’ individual components to enable an informed decision to be made on the refurbishment requirements for each campaign. The results of the stepped RBA process demonstrate the effectiveness of the approach to define and manage a refurbishment program that achieves the required extended service life of the structures to 2040. The RBA process enabled the first campaign’s scope to be minimised through detailed analysis and calculation of residual design life of each critical member, deferring most of the refurbishment scope to the second campaign in 2030. The study has recommended implementation of a corrosion rate trial to verify the assumed corrosion rates for the jetty structures. Environmental monitoring stations and test coupons installed on the jetty for a five-year period will confirm the actual deterioration rates specific to the jetty structures. Confirmation of actual deterioration rates may reduce uncertainty in the values over those currently assumed in the study and positively affect the identified Phase 2 refurbishment scope.