LNG Ship Tank Inspection Priorities from Sloshing Wear History
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Solution Overview
Problem
The existing methods for managing maintenance of liquefied gas tanks on ships are inefficient, as they often require complete tank emptying for inspections, leading to costly immobilization and potential unnecessary downtime, despite the risk of sloshing-induced damage and the challenge of identifying damaged tanks without thorough inspections.
Innovation Solution
A method to determine a 'wear index' for each tank based on historical and real-time sloshing indices, allowing for targeted inspections only when the index exceeds a set threshold, thereby optimizing maintenance operations and reducing unnecessary tank inspections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complete tank inspection is performed, then detection precision of tank damage is improved, but loss of time and productivity deteriorates due to vessel immobilization
Solution Approach 1:
The system performs preliminary monitoring and assessment of tank conditions during normal operation using sensors and data collection. Wear indices are calculated in advance based on accumulated data, allowing the system to identify tanks that truly need inspection before the vessel arrives at port, eliminating the need for routine complete inspections of all tanks.
Solution Approach 2:
Instead of performing complete inspections on all tanks, the system applies partial action by conducting inspections only on tanks whose wear indices exceed predetermined thresholds. This selective approach focuses resources on high-risk tanks while avoiding unnecessary immobilization for low-risk tanks.
2Reliability
If frequent tank inspections are conducted, then reliability of tank integrity is improved, but productivity and operational efficiency deteriorate due to repeated immobilization
Solution Approach 1:
The system continuously monitors tank conditions and calculates wear indices based on accumulated operational data, creating a feedback loop that dynamically adjusts inspection priorities. This feedback mechanism ensures inspections are triggered only when actual wear thresholds are approached, maintaining reliability while optimizing productivity.
Solution Approach 2:
The inspection schedule is made dynamic rather than static. Tanks are monitored continuously and inspection timing is adjusted based on real-time wear index calculations, allowing the system to adapt inspection frequency to actual tank conditions and operational patterns.
3Measurement precision
If comprehensive tank monitoring is implemented, then detection precision of wear patterns is improved, but device complexity and cost increase
Solution Approach 1:
The system uses an intermediary computational model (wear index calculation algorithm) that processes sensor data and operational parameters to generate meaningful inspection priorities. This intermediary layer translates complex multi-parameter data into simple, actionable wear indices that drive inspection decisions without requiring complex real-time analysis infrastructure.
4Reliability
If preventive maintenance is performed on all tanks, then reliability is improved, but loss of time increases due to unnecessary inspections of low-risk tanks
Solution Approach 1:
The system applies local quality by treating each tank individually based on its specific wear index rather than applying uniform maintenance to all tanks. Tanks with high wear indices receive preventive attention while tanks with low wear indices continue normal operation, optimizing the balance between reliability and operational time.
Data Source
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AI summary
The invention relates to a method for managing maintenance for a ship comprising a sealed and thermally insulating tank for transporting liquefied gas. The method comprises the steps consisting in determining 310 a current filling level of the tank, determining 320 a current state of movement of the ship, determining 330 a current sloshing index IBi from the current filling level of the tank and the current state of movement of the ship, taking into account the position and the geometry of the tank, integrating 340 the determined current sloshing index IBi into a wear index lUi that takes into account a history of the sloshing indices. The wear index is then compared to a threshold in order to indicate if the tank needs to be inspected, depending on the result of the comparison.