Hirofumi Takano
ClassNK Tokyo
Floating liquefied natural gas (FLNG) promises to revolutionize the LNG industry, but it also poses huge challenges for shipyards, equipment manufacturers, and class societies.
Although the majority of LNG developments are onshore, FLNG is expected to provide an economical option to building onshore liquefaction facilities. If successful, FLNG systems also could avoid the land rights and environmental concerns raised by onshore LNG development.
Topside arrangements and cargo storage equipment must not compromise safety onboard LNG FPSOs.
At the same time, FLNG requires less capex than onshore developments and therefore will allow development of stranded medium and small gas fields that would not have been possible to develop previously. In order to make this happen shipyards will need to establish practical methods to develop the high value-added systems required for these projects. At the same time, plant makers and other equipment manufacturers will need to devise smaller, highly efficient, and highly reliable systems for use on these facilities.
Classification societies will need to develop new systems to analyze the safety of floating structures, as well as new tools to better support shipyards and planners in the FLNG design process. And, as the majority of FLNG facilities will need to be registered with a flag administration, classification societies will have an important role to play in ensuring the safety and security of such institutions.
ClassNK is addressing these challenges through its recently established Resources & Energy Development Project Team that supports the entire range of energy development activities including upstream exploration, midstream transportation, and downstream receiving and storage.
Key issues include the lack of a track record for natural gas production on marine floating structures directly exposed to waves; unproven reliability of new offloading systems; increased difficulty in responding to incidents at sea due to limited accessibility; and limited access for maintenance.
To address these issues, ClassNK is working proactively with manufacturers, shipyards, and operators to analyze the current development environment, and, via joint industry projects and other projects, is striving to formulate workable solutions. For example, the group is working on several projects which have great potential to solve some of these difficult challenges, including development of a highly accurate ship motion analysis system, as well as new inspection and survey schemes which use simple monitoring tools.
From the development of new cargo hoses to effective inspection systems for use during operation, there is a great demand for new technologies and equipment to ensure the safety of FLNG facilities and operations. ClassNK hopes that through these new technologies, as well as related regulations and guidelines, it can help contribute to FLNG development.
Risk analysis
In the new guidelines for FLNG released at the end of February 2011, ClassNK proposes a fatigue and coating condition monitoring scheme using well-proven monitoring sensors or coupons. These would allow owners and operators to track the condition of their floating facilities in either real-time or at predetermined intervals. The society also champions the use of risk assessment as an essential tool to ensure safety, as well as environmental and asset protection.
The containment system is an area of particular interest. Requirements for FLNG facilities differ from those of LNG carriers. Some issues, such as sloshing, are of greater concern for FLNG than for LNG vessels. At the same time, others factors such as rapid cool down time are of less importance.
Structural integrity is paramount to ensure the overall safety of FLNG cargo containment. By combining the latest condition monitoring tools with the results of the latest research and cutting-edge fatigue strength assessment, the structural safety of FLNG is constantly maintained.
As the storage tanks of FLNG facilities are very similar structurally to the highly reliable systems found on LNG vessels, in some aspects the containment requirements are similar. However, there are three important additional factors to address for FLNG facilities.
Unlike LNG vessels, FLNG facilities operate in partially loaded conditions in various sea states for extended periods of time. As such, it is essential to use designs which are reliable in the face of sloshing loads. As it is difficult for FLNG facilities to enter dry dock for repair, the FLNG facility needs to be able to be maintained while moored and be robust enough not to require serious repairs for extended periods of time.
Thirdly, efficient topside arrangements require a large amount of deck space. So, care needs to be taken in the choice of cargo storage equipment, as well as the overall topside arrangement, to balance safety concerns with ease of maintenance. The importance of these factors is recognized throughout the FLNG industry and, efforts are under way to develop new technologies to address these problems.
Key technical issues that remain to be addressed include:
- Topsides: Due to limited space, topside equipment needs to be as small as feasibly allowed. At the same time, however, as this equipment is being installed on a floating structure, risks need to be reduced as much as possible, and equipment needs to be fully functional even in rough conditions.
- Hull: Extended periods without docking need to be considered in almost every aspect of hull design, including determination of initial dimensions, fatigue strength confirmation, implementation of fire resistant/fire preventive design elements and systems, and development of maintenance procedures.
- Mooring: Mooring systems must not interfere with production and offloading operations, and must be able to separate in the event of an emergency.
- Offloading: Offloading systems must cope with the movement of two floating structures and, at the same time, systems designs must take into account the limited track record and experience with LNG ship-to-ship (STS) transfers.
