LNG 추진 선박 및 LNG 유조선의 안전 규정에 관한 연구. 본 연구에서는 LNG 추진선과 LNG 운반선의 안전성을 강화하고 관련 규정을 검토하였다. 첫 번째 연구에서는 IGC 코드와 IGF 코드의 안전 규정에 대한 비교 분석(Gap 분석)을 수행했습니다.
Introduction
Background
On the other hand, people can hide the fact that LNG is a more dangerous substance that can be fired or exploded if given the opportunity to ignite. Due to these characteristics of LNG, regulations on LNG powered ships and gas carriers have played a crucial role in covering the risk created by LNG. As several regulations have recently been developed, we must not only ensure a greater degree of commonality between the diverse regulations we have today, but also verify that applied regulations have been properly developed.
Aim and objectives
The type of fire and explosion may depend on the surrounding conditions whether they are open or closed. Given the risk that can be expressed as a combination of probability and consequence, the safety issues associated with the transportation or use of LNG for marine purposes must be properly understood and addressed. To improve the understanding of LNG safety in the maritime domain, as well as to undertake a critical review of the current regulatory framework.
Literature review
- IGC Code
- IGF Code
- Harmonization between IGC code and IGF Code
- Revised requirement on filling limit in LNG Carrier
Moreover, different working groups in IMO were so dedicated to each code that the safety requirements of the two codes were considered to be different. Much of the new IGC code is reflected in best practice applied to the latest LNG carriers in the marine industry. Such an improvement of the new IGC code was originally borrowed from IACS recommendation 109 developed in 2009.
Methodologies
Research method applied in gap analysis between the IGC Code and the
Approach applied in the study on the adequacy of the revised regulation
In this chapter, a gap analysis is provided that identifies the differences or inconsistencies between the safety requirements for LNG ships and LNG-powered ships in accordance with the IGC and IGF codes. According to IGF Code 5.4, LNG-powered ships must meet one of the two machinery concepts: either 'gas-proof machinery space' or 'ESD-protected machinery space' (IMO 2015c). Meanwhile, a regulatory difference was identified: while both engine spaces are applicable to LNG-powered ships based on the IGF Code, the IGC Code only accepts the gas-proof engine space concept for LNG ships.
Also, the IGF code 9.7 limits the pressure of the gas fuel supply system for gas engines in the ESD-protected machinery space to 10 bar. The tank connection space concept described in the IGF Code is compared with the equivalence of the IGC Code in Table 5. Regulatory imbalances are also reflected in the safety requirements for the application of the duct and double-walled pipes shown in Table 10.
Therefore, the LNG-powered ships are subject to a number of different regulations for ventilation inlets of the double-walled pipes and the canal (IMO 2016b). In this study, a gap analysis was carried out to identify the differences or discrepancies in the safety requirements for LNG ships and LNG-powered ships in accordance with the IGC and the IGF codes. This study examined a regulatory discrepancy regarding the LNG cargo tank filling limit between the original and the new IGC code.
Working Group Report, Amendments to the IGF Code and Development of Guidelines for Low Flash Point Fuels.
Study 1: Regulatory gaps between LNG carriers and LNG fuelled ships
Gap analysis between IGF Code and IGC Code
- Risk assessment
- Machinery space concept
- Fuel containment system (LNG storage tank)
- Tank location
- An arrangement of tank pipe connection
- Arrangement of pressure relief system
- Control of tank pressure and temperature
- Safety systems
- Piping design
- Water spray system
- Duct and double wall pipes in machinery space
- Duct and double wall pipes outside machinery space
- Ventilation
- Cargo manifold / bunkering station
- Miscellaneous systems
- Temperature indicator
- Gas detection
In the concept of the gas-proof engine room, a single fault must not cause a gas leak in the engine room. Unlike the gas-proof engine room, gas leakage can be released into the engine room under the concept of the ESD-protected engine room in the event of such an accident. On the other hand, the ESD-protected engine room is focused on the post-treatment of the initial gas leak.
Alternatively, the probabilistic approach to the distance of the LNG tank can be used more flexibly without compromising the safety aspect. In this context, the IGF Code 5.3.4 alone introduced the probabilistic approach to determine the safety distance using the concept of damage stability analysis in accordance with SOLAS II-1 (IMO 2013a; IMO 2014a, 2014b). Pipes mounted on the head of the LNG cargo tank must be installed above the highest LNG level in the tanks (IGC code 5.5.2.1); When using a type C fuel tank with tank connection space, the pipes can be connected below the highest liquid level according to IGF code 6.3.5.
It therefore considered that the level of safety requirements of the IGF Code should be linked to a risk-based approach rather than to the size of the ship. According to IGF Code 6.9.1.1, the pressure and temperature of LNG fuel tanks must be monitored and maintained for a minimum of 15 days after the initial activation of these safety systems. However, the IGF Code additionally requires that piping systems with a maximum working pressure of 1.0 MPa or higher, regardless of design temperature, be subject to such an analysis (IMO 2015c).
On the other hand, the IMO Subcommittee on Carriage of Cargoes and Containers (CCC) was of the opinion that the interpretive text for IGF Code is not necessarily compatible with the IGC Code. The installation of the vapor return line is considered optional for LNG powered ships, while it is mandatory for the vessels subject to the IGC code as described in Table 13. Given the fact that the IGC code for LNG carriers, or related standards , do not specify the need of the safety zone for LNG cargo transfer, the safety requirements on the LNG bunkering can be considered strict.
Result and discussion
Openings for the ventilation inlets and outlets of the twin pipes to the engine room are accepted. The main basis of the IGF Code for ships using LNG as marine fuel is the experience and knowledge of similar LNG ship systems. Therefore, in particular, they need to be reviewed and revised based on a proper systematic risk assessment of LNG-powered ships.
In this context, this study is believed to provide a useful guide in increasing a general understanding of the similarities and inconsistencies between the two Codes. Vapor bag occurrence: In this study, only double hull damage (no cargo tanks) was considered when considering the vapor bag scenario. Environmental condition (opened or clogged condition): The condition of the leakage from the ventilation tower was considered as “opened condition”.
Since the total cost of the alternative case is higher than that of the base case, it can be said that the base case is more desirable than the alternative scenario. It can be assumed that this statement confirms the inadequacy of the new requirements of the IGC Code on the filling limit. MSC 83/INF.3 FSA - Liquefied Natural Gas (LNG) Carriers Details of the Formal Safety Assessment London, London: International Maritime Organization.
Comments on the Report of the Correspondence Group for the Development of the Draft International Code on the Safety of Gas-Fired Ships (IGF Code).
Study 2: Investigation on the adequacy of the revised regulation of filling
Case Study
- Step 1: scenario identification
- Step 2: Analyses
- Economic analysis
- Environmental analysis
- Risk analysis
- Step 3: Integration
- Step 4 - Evaluation of the best scenario
In this context, this study assumed that the alternative scenario would require one more trip to transport the remainder. The relevant data for these accident scenarios was based on MSC 83/INF.3 "FSA-Liquefied Natural Gas(LNG) Carriers Details of the Formal Safety Assessment". Cargo hold damage or not: Regarding the possibility of vapor pockets, list condition is more critical than trim condition due to the shape of the tank.
An LNG leak from a cargo tank has a significantly higher risk than a vent mast leak due to a vapor pocket. As stated above, an isolated vapor pocket shall not form in a cargo tank under the liner and list specified in 8.2.17 of the IGC Code if a fill limit greater than the 98% limit is permitted. In light of this, the assumption that the chance for the base scenario (98%) of the occurrence of an isolated vapor pocket in the case of an overtilt or trim condition was considered zero in this study, while 100% for the alternative scenario (98.5%) .
Nevertheless, a conservative assumption was made that "if an isolated vapor pocket is created, overflow from the vent column always occurs". However, in this analysis, we have taken a conservative view where assuming all random frequencies for the vapor pocket may result in the release of LNG. Given that all impacts have been converted into monetary values, the result plots represent the total costs for each scenario.
However, other vessels, which had more than 30 days for a single trip, revealed that the total cost of alternative scenario is higher than the base one.
Discussion
The results are believed to provide stakeholders with insight into the demonstration of the inadequacy of the new regulation. This paper concluded that the LNG fill limit should be reset to 98.5% as it shows the holistic benefits of such a scenario. Therefore, it revealed that the over-regulation to be considered could impose serious commercial, financial and administrative burdens on national authorities and industry.
Therefore, it can be assumed that the appropriate level of regulation is essential to avoid negative effects on the sustainable development of shipping and trade. Through the gap analysis, it was found that the LNG powered ships are generally subject to a higher level of safety under the IGF Code compared to the equivalents for LNG ships in the IGC Code. However, it should be noted that at least the same level of security requirements must be applied where the same systems and arrangements are used.
In particular, the following parts in the IGC Code and the IGF Code were proposed to go through a rigorous revision to bridge the safety requirement gaps for the engine room system: the machinery space concept (chapter 3.1.2), the analysis of stress in system piping (chapter 3.1.4.1) and safety requirements for ducts and double-walled pipes (chapter 3.1.4.3) and ventilation (chapter 3.1.4.5) discussed in this study. Finally, it is important to note that the use of the proposed multi-criteria decision-making process is expected to contribute to the strengthening of the future regulatory process towards a probabilistic and realistic evidence-based path rather than a deterministic one. International Code of Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code), Resolution MSC.370(93) adopted on 22 May 2014.
Editorial clarifications necessary to ensure uniform application of risk assessment in relation to part A-1 of the draft IGF Code, MSC95/3/15 (China, Germany, Japan, Republic of Korea, Spain and CESA).
