Model-Based Safety Analysis and Design Enhancement of a Marine LNG Fuel Feeding System

Konstantinos Milioulis,Victor Bolbot,Gerasimos Theotokatos

doi:10.3390/jmse9010069

Konstantinos Milioulis, Victor Bolbot + Show 1 more

Open Access

https://doi.org/10.3390/jmse9010069

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Abstract

Recent regulatory requirements for shipping emissions control have led to the adoption of Liquefied Natural Gas (LNG) as a marine fuel and the design of LNG-fuelled vessels. Considering the potential safety implications due to system failure/unavailability, this study aims at the safety analysis of a low-pressure LNG fuel feeding system using a novel model-based methodology. The proposed methodology is based on the functional system modelling, leading to the failure diagrams development, and combines the use of Failure Modes, Effects, and Criticality Analysis (FMECA) and Fault Tree Analysis (FTA), which are performed in MADe™ and PTC Windchill software environments. The FMECA results are employed to identify the investigated system critical components and failures as well as specifying the top events for the subsequently performed FTA, which evaluates the top events failure rates. The system critical components identification leads to the system design modification targeting reduced safety metrics. This study results demonstrate that the evaporator, pressure build-up unit, sensors, and cryogenic valve assemblies are the most critical components of the investigated system, whilst the enhanced system design exhibits a failure rate reduced by 69% in comparison to the baseline system. This study reveals the advantages of the developed methodology along with some limitations of the employed tools and contributes to the quantitative safety analysis and design of ship complex systems.

Highlights

More than 500 vessels fuelled by Liquefied Natural Gas (LNG) have been in operation by 2020, which is mostly attributed to the lower natural gas prices in comparison to past and the global sulphur cap imposed in the same year [7]
The main advantage of MADeTM is the effective development of the system functional model that allows for the investigation of the system failure propagation, supporting the identification of the system critical components and their failure end-effects
This study proposed a novel methodology for the ships systems quantitative modelbased safety analysis, which combines the system functional modelling, the failure propagation analysis, FMECA, and Fault Tree Analysis (FTA)

Summary

Introduction

Liquified Natural Gas (LNG) has become an attractive and cost-effective solution that reduces a ship’s environmental footprint, ensuring compliance with existing and forthcoming legislation [1]. The LNG feasibility and comparative assessment to other alternative fuels and after-treatment technologies were demonstrated by various studies [1,2,3,4,5]. Ships that use LNG as their primary fuel vary both in type and size. Recent engine developments allowed for the use of dual-fuel engines of both the low- and high-pressure types [6]. More than 500 vessels fuelled by LNG have been in operation by 2020, which is mostly attributed to the lower natural gas prices in comparison to past and the global sulphur cap imposed in the same year [7]

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