With more than 800 LNG-fuelled ships in the global fleet, the Society for Gas as a Marine Fuel (SGMF) has issued a technical guidance note (TGN) supporting best practices for filling and loading LNG fuel tanks
Called LNG Fuel Tanks – Loading/Filling Limits and Level Instrumentation: Considerations and Recommendations, the TGN provides clarity for those partaking in, monitoring or managing LNG bunkering operations.
“Our overall purpose was to provide effective guidance on the rules for filling and loading and to explain why the loading limit may vary for each bunkering operation due to LNG temperature, pressure and composition,” said SGMF general manager Mark Bell. “The crew can then maximise the amount of fuel that can be safely loaded by following established bunkering procedures and using the available instrumentation,” he added.
The inherent properties of LNG, in particular its cryogenic nature and behaviour, differ significantly from those of conventional marine fuels. This means the quantity of fuel that can safely be loaded into fuel tanks on gas-fuelled vessels will depend not only on the size and capacity of the tank itself but also on the temperature and pressure of the LNG to be bunkered.
Statutory safety limits on filling and loading LNG fuel tanks are set out in codes and regulations, most notably the International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels (IGF Code). However, the methods by which the filling and loading limits should be calculated for LNG fuel tanks have been interpreted differently by some vessels in operation and under construction, depending on the tank type, shipyard or classification society.
These differing interpretations have led to some vessels applying a lower loading limit, reducing the amount of LNG in tanks. Despite safety not being affected, the fact that less LNG is being carried clearly has an impact on the vessels’ autonomy and inservice operations.
This new publication provides practical recommendations that go beyond the statutory requirements to ensure vessels do not only operate safely, but also efficiently and in an environmentally responsible way.
Also included in this guidance are lessons learned to promote best practices and form a basis for common understanding between the main stakeholders involved. Gas-fuelled vessels and bunkering facility owners and operators, as well as LNG tank and fuel system designers, should consider the recommendations when defining and developing vessels’ specific systems, equipment and LNG bunkering operational procedures.
An example of operational levels and thresholds that might be used as reference for an LNG fuel tank is provided, along with sample loading tables and detailed information about the types of LNG fuel tank, their calibration, level instrumentation and functionality.
Carnival Corp LNG project director Stuart Carpenter, who was TGN’s working group chair, emphasises the real-world expertise that has fed into the guidance, noting it draws “on a vast repository of operational and inservice experience from our working group members (who included vessel operators, tank manufacturers and system designers).”
Such guidance based on real-world experience is valuable, as LNG bunkering is expected to continue to grow to support the rapidly expanding global fleet. Some 100 ports globally currently offer LNG bunkering.
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