FSRUs and FSUs provide a fast and flexible approach to developing gas terminal infrastructure, explains BV global market leader tankers & gas carriers Carlos Guerrero
Operators considering a floating terminal approach to meeting LNG import infrastructure requirements have a number of options to consider:
- Conversion or newbuild?
- Near-shore or offshore location?
- Preference for a fixed location?
- FSRU/FSU – a ship or a regasification/storage barge?
- Storage only?
These operational options need to be enabled and supported by the best technical insight and, vitally, compliant with appropriate regulatory regimes and standards.
From our perspective, the fundamental issue is whether to follow a ‘marine’ approach to addressing risk, akin to the risks addressed through classification ship rules and under SOLAS, or to adopt a risk approach more like that of the offshore industry.
“Class and statutory rules for ships could be too conservative for operations in very mild weather areas and inadequate in others”
Simply put, the marine approach would be suitable for an LNG carrier which, with some modification, could be used as a floating reception and storage terminal. However, at the offshore end of the spectrum, a floating storage and regasification unit (FSRU) or floating storage unit (FSU) newbuilding might have no propulsion capability and a non-hydrodynamic hull form. It would effectively be a floating barge envisioned, and intended, to be moved only very seldom and designed to be moored in very sheltered waters.
Location is important for the design and regulatory options, as well as operational requirements. Trading LNG carriers are designed to sail either in a fully laden condition – from the export to the import gas terminal – or almost empty, with a slight ‘heel’ of LNG to keep tanks cool and to provide bunker fuel when they return to load. LNG carriers do not generally sail with cargo tanks partially filled. Loading and discharging are performed at sheltered gas terminals where the ship is stationary.
But a regasification LNG carrier acting as an FSRU will normally be expected to operate with tanks at all ranges of fill level. The sloshing of the cargo may generate huge impact loads on tank bulkheads, containment system boundaries and pump towers, which must be designed and reinforced accordingly.
And the further away the mooring is from the shore, the more exposed the ship is to significant sea states and wave conditions. In the calm, protected environment of a port, transferring liquefied gas by flexible hoses from one ship to another is certainly not a picnic party; but it is no more complicated than discharging to an onshore LNG terminal.
The crew of an LNG carrier is well trained for the ship-to-ship (STS) transfer operation and fully aware of the potential dangers, not only for the people on deck, but also the risks of leaking liquefied gas which, at -160˚C, which may cause severe damage to the steel deck structure.
Class and statutory rules for ships could be too conservative for operations in very mild weather areas and inadequate in others. Class rules for offshore units usually allow design optimisation against actual site and operational conditions.
Seen from the perspective of the shipowner, there might be an opportunity to save unnecessary steel weight or to gain cargo capacity. Terminal siting and mooring are specific areas of expertise that require expert support and modelling, combining analysis of location, weather and sea conditions, marine traffic and geophysical conditions.
With one leg in ‘marine’ and one in ‘offshore’, most FSRU/FSU projects raise technical, regulatory, operational and environmental issues and questions - from all stakeholders.
Carlos Guerrero will be speaking at the LNG Ship/Shore Interface Conference Europe, held in London on 22-23 November 2018. For more information, please visit https://www.lngshippingconference.com/index.htm