FSRUs, FSUs and small-scale LNG need common standards - Trelleborg Marine Systems

FSRUs, FSUs and small-scale LNG need common standards


Gastech 2017, Andrew Stafford

Trelleborg technical director marine systems operation Andrew Stafford calls for industry standards for floating import vessels and small-scale LNG to make interfaces more compatible 

When managing floating storage and regasification unit (FSRU) operations, the ship-to-shore interfaces for gas output, and interfaces between LNG carriers (LNGC) and FSRUs for liquid transfer are mission-critical.

The ship-shore Link (SSL) is part of the emergency shutdown (ESD) and safety chain across this interface, carrying communications and data between ship and shore or between floating assets. A backward compatible high-speed digital design was developed in 2005-2007 to overcome the limited functionality of legacy SSL systems.

With the implementation of FSRUs and floating storage units (FSUs) in 2007-2008 requiring transfer support for multiple processes, this digital design proved an ideal solution. However, regulatory standards took a while to catch up.

In 2011, an ISO standard was released covering key compatibility aspects of the traditional large scale LNGC ship-shore interface, but still nothing to cover the FSU/FSRU interface.

Compatibility for FSRUs and FSUs

In the absence of relevant standards, new FSRU-FSU projects are being designed in isolation. Arbtrary bespoke interfaces have been developed without thought for wider compatibility. Requirements for ultra-fast Ethernet links via legacy fibre-optic infrastructure, as well as via standard instrument cable, have been seen without regard for feasibility of implementation or compatibility with other applications.

The further development of mooring arrangements for double bank and direct ship-to-ship transfers have introduced the installation of quick release hooks with integrated load monitoring on board vessels.

These require more complex interfacing between the FSRU or FSU and the LNGC, in effect turning an FSRU or FSU ship into a shore, while retaining the flexibility for the FSRU or FSU ship to return to trade as an LNG carrier. Meanwhile, the emergence of small-scale and LNG bunkering is only adding to the debate.

The large-scale LNG marine transfer industry has used linked shutdown systems since the mid-1970s. The primary function of the link is to mutually shut down the connected counterpart system in the case of an ESD condition being raised on the local system.

Several connectors started to offer additional functionality, beginning with telecoms and followed by mooring load with environmental data and more recently Ethernet and process data.

Although the connectors used ended up as standard, the pin configurations within the connectors were open to interpretation by the original system integrators, leading most terminal installations pre-2000 to use bespoke configurations.

Work on standardising ship-shore links was undertaken around 2009, with the publication of the Society of International Gas Tanker & Terminal Operators (SIGTTO) document ESD Arrangements and Linked Ship/Shore Systems for Liquefied Gas Carriers. Then came ISO 28460:2010, which defined standard pinouts for the 37-pin and Miyaki type systems.

These have had a positive influence on newbuild facilities. However, existing terminals have not moved to the standard pin-out, meaning vessels are still required to configure per terminal. What’s more, both publications focus on the transfer of LNG in bulk, and do not directly cover the newer application of FSRU, FSU and small-scale and LNG fuelling.

This means that these newer markets are subject to interpretation of existing guidance plus project-by-project bespoke developments.

FSRU compatibility

The first FSRU vessels were delivered around 2005, installed with traditional SSL equipment. This was more than adequate for the initial applications of FSRU compressed natural gas (CNG) discharge at a jetty, or for offshore buoy with LNG reloading via ship-to-ship transfer, while removed from the jetty.

Increasingly complex operations soon required concurrent and independent discharge of CNG and reloading of LNG. This requirement introduced the concept of dual ESD, which was not possible using existing SSL systems.

Additionally, with FSRU terminals being built by and for domestic utility companies, there was a requirement for gas volumes and qualities to be shared by the FSRU to the terminal.

Newer implementations are now being conceived to simplify the terminal to a simple tie-in location, with the entire process being managed by the FSRU. This started with sending a few shore data values for temperature and pressure at a national grid tie-in point.

More recent discussions concern the level of control the FSRU should have at the jetty; specifications are being written and implemented to allow the FSRU to release both the shore quick-release hooks and the shoreside loading arm powered emergency release couplings.

FSU compatibility

FSU applications typically originate from conversions of existing LNG carriers. During conversion, there is a preference to re-use as much of the pre-existing installation as possible. For ship-shore links, there will be an SSL ship system on board, but techniques used in the original fibre-optic links mean that an LNG carrier link can only ever connect fully to a terminal system.

Historically, the optical fibre has never offered a ship-ship mode for both ESD and telephony due to compatibility issues. As an FSU is, in effect, the storage extension of a shore facility, increased integration between the FSU and terminal is critical.

Existing fibre optic cabling performance must be addressed, as the original SSL fibre optic specification is for a 50/125µm OM2 offering limited bandwidth over distance. User expectations for high speed and long distances need to be managed as it may not be possible to implement this link using existing infrastructure.

Depending on the facility, there may be a requirement for enhanced input/output (I/O) signalling between terminal and vessel. If the signal needs high integrity, such as an additional level of shutdown, then a hardware based I/O channel within the core SONET packet structure can be implemented.

However, for process control I/O, if serial data is not an option, then third-party distributed I/O hardware modules can be implemented with the SONET Ethernet.

Small-scale compatibility

The emerging small-scale LNG applications presented a crossroads for the industry, in terms of ship-shore link compatibilities and functionality. The first option is to retain the bespoke links and allow the small-scale market to inherit existing large-scale system types with their limited functionality.

Alternatively, there is the opportunity to standardise and simplify new vessels by using up-to-date and international standard technologies. This future-proofs the industry and creates flexible trading assets.

Building on the SONET technology, now well-proven in the FSRU market, small-scale shutdown links could integrate the ESD, telecoms and process control functions within a simple link.

Trelleborg Universal Safety Link is installed on some of the leading projects in the sector and offers operators a new level of oversight and control for the LNG-transfer market. Process data for the remotely connected system can be displayed and made available to the local operator and the network link has enabled full control DCS interlink between vessels and terminals.

There are special-case considerations for intermediate vessels that could load from an existing large-scale facility and distribute to smaller customers. In this case, the asset needs to be equipped for connection to the legacy system and the new small-scale systems.

As the small-scale technology is based on that contained in FSRU applications, cost-effective solutions allowing connection to all applications exist.

Conclusions

The proliferation of standards today reflects the piecemeal evolution of the large-scale LNG market – something the industry is still addressing today. Although ISO standards are now in place, there has been no modification to the configuration of existing terminals that do not conform to the standard pin-out.

This is forcing LNG carriers to install complicated configurable systems that could lead to delayed connections.

As newer fleets of FSRU and FSU vessels are constructed, there is no common standard to build to. Although there has been much attention paid to ensuring links have compatible connectors and signal transmission format, application data is being implemented at a local level that does not lead to standardisation. In an industry that requires worldwide compatibility, this represents a major challenge.

The time is right to form an industry working group to look at the requirements of standard data and interfacing to generate a core specification. This core specification could then be adopted as standard practice into future guidelines helping to reduce project timeframes and simplify integration between systems.

This article is also published on:
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LNG Industry (PDF)
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