FLNG market trends: Fluid handling solutions for buoyant FLNG industry

By Vincent Lagarrigue, Trelleborg

Seawater intake risers provide a dedicated solution to cooling process challenges FLNG facilities
Seawater intake risers provide a dedicated solution to cooling process challenges FLNG facilities (photo: Trelleborg)

Over the next few years, the FLNG market is projected to witness significant gains, against a backdrop of increased global gas consumption, energy security programs and a paradigm shift in marine fuel preference. According to an analysis of sanctioned and upcoming projects by Westwood Global Energy Group, global FLNG capital expenditure (capex) is projected to total USD 52.8 billion over the 2019-2024 period.

The growth of the market is underpinned by a number of new FLNG projects, including Exmar’s Tango FLNG, which arrived at its new home in Argentina last month. There it will undergo outfitting and commissioning before producing its first LNG cargo in Q2 2019. As the first floating liquefaction unit to operate in the Americas, the project represents a significant milestone in FLNG’s trajectory to the mainstream, and a reminder of its commercial and technical viability over traditional onshore liquefaction plants. Benefits include a short construction period, cost efficiency, environmental viability, and mobility.

In a bid to remain competitive and attractive to investors, FLNG projects will look for further cost reductions and innovations. However, the need to reduce opex requires detailed attention to every aspect of operations. One of these is fluid handling, an essential part of the safe operation of an FLNG. Used to bring huge quantities of cold water onto floating production platforms to absorb the heat generated when natural gas is compressed and liquified, seawater intake risers are a vital part of any FLNG operation. In some cases, as much as 40,000 cubic metres of water per hour is needed to absorb the calories exhausted, requiring systems with high flow rates and a long lifespan of up to 25 years.

Hybrid seawater intake risers

The SWILINE is a submarine flexible water intake hose for FLNG cooling applications
The SWILINE is a submarine flexible water intake hose for FLNG cooling applications (photo: Trelleborg)

One of the trends that we’re now seeing as a result of this challenging market environment is an increased demand for hybrid seawater intake risers (SWIRs) using a combination of HDPE plastic pipes and rubber hose technology. At the same time, there is an increased demand for SWIR’s to reach a lower water depth, as the cooler water increases performance and improves the global efficiency of the liquefaction process. While hybrid solutions using plastic pipes can offer cost savings in the region of 20-30%, there are a number of risks involved that must be considered when choosing the right solution.

From a technical standpoint, the use of HDPE is particularly challenging due to its buoyant nature and the complex viscoelastic behaviour of the material, particularly when it comes to assessing its fatigue life. As the density of the plastic used is less than seawater, a HDPE riser must be weighted down to stop it floating in the water and to ensure the strainer is at the lowest possible depth. Ballast weighting is also required for stabilising purposes versus current and waves effect. All of this puts a huge amount of stress on the riser, posing a serious risk to both the vessel and the assets on the seabed if the plastic pipes were to break.

Customers also need to be aware of the operational challenges inherent in hybrid systems, particularly when compared with complete rubber hose solutions. For example, our Swiline hoses are designed to be used in lengths of up to 800 metres or even more, enabling the use of seawater from greater depths, which can be up to 25° C (77° F) cooler than water at the surface. Hybrid systems, on the other hand, will operate in much shallower depths, resulting in warmer water being used during the liquefaction process.

Pushing the boundaries
For an effective cooling process, it’s vital that seawater is as cold as possible. Therefore, while hybrid hoses might be cheaper in terms of capex, customers may wish to consider using a solution consisting solely of rubber hoses rather than a hybrid solution to maximise long term performance.

In 2016, Trelleborg Oil and Marine launched its dedicated seawater intake hose solution, which once again pushed the boundaries of technology in the oil and gas sector. Our Swiline hoses are fully certified to the API 17K specification, which certifies up to 30 years’ maintenance-free service life with a safety factor of 10.

SWIR strainer
SWIR strainer (photo: Trelleborg)

Employing a unique design incorporating an integrated bending stiffener with a continuous inner liner and rubber outer cover, the hoses minimise the risk of corrosion while offering optimal thermal insulation. The combination of steel cables in a rubber matrix minimises creep and offers typical tensile strength as high as 1,600 tonnes for 40-inch inner diameter (ID) hose – a key attribute when the higher weights required to maintain the position of the hose in high currents are considered.

Swiline hoses can be easily installed vertically from the FLNG deck. Assembly can take place beside the hull with connection on the intake flange by divers, or in the riser caisson without diver assistance.

Our field-proven solutions have already been used on two FLNG projects worldwide, including the Shell Prelude project – the world’s largest FLNG, located in the Timor Sea, where production commenced late last year.

Loading and offloading
The selection of optimum fluid handling equipment is also essential when it comes to loading and offloading, and many of the same principles apply. Many solutions which could potentially reduce the effect of motion and weather have been considered. However, to date, in the main, traditional LNG loading arms have been adapted to enable LNG ship-to-ship transfers in open water via a side-by-side configuration.

While loading arms are designed to handle both liquids and gases in a wide range of viscosities and temperatures, environmental constraints, such as tidal and wind conditions, and the effect of earth movement can have a significant effect on the performance of loading arms. With the prospect of new FLNG locations being established in sites with substantial gas reserves but where sea conditions can be much more severe, this straightforward equipment might not suffice, resulting in potential safety issues and even in shutdown of the liquefaction plant with costly associated downtime.

For over 20 years, the solution the most widely considered by the oil industry to go beyond the limitations of side-by-side offloading has been the tandem offloading configuration. Whereas side-by-side offloading configuration is merely used in less than 10% of existing FPSO’s in the world, the tandem offloading configuration is extensively used all over the world in the most demanding sea states conditions (e.g. Norway, Australia, Brazil). This can be explained by the strong reliability records compared to other solutions and the perception of lower risks on the safety perspective. Moving the tanker away from the side of the floating production unit significantly decreases the risk of collision between the two vessels and the risk of escalation in case of accident, fire or blast on one of the vessels.

Cryogenic hoses

CRYOLINE – a hose-in-hose concept that consists of a field-proven outer rubber marine hose with an inner LNG composite hose
CRYOLINE – a hose-in-hose concept that consists of a field-proven outer rubber marine hose with an inner LNG composite hose (illustration: Trelleborg)

A viable solution for tandem offloading is the use of cryogenic floating hoses as it significantly relaxes the constraints. The distance between the vessels can be easily increased up to safe distance without impacting the design of the structure. The positioning constraint of the LNG carrier relative to the floating production unit may allow larger sway excursions or tolerate higher fish tailing motions from the LNG facility – a configuration that is similar to the oil tandem offloading practices that the operators are very much familiar with.

Trelleborg’s own cryogenic hose technology – ranging from 150 mm to 500 mm ID – is based on a hose-in-hose concept that consists of a field-proven outer rubber marine hose with an inner LNG composite hose – a configuration that is already well established, in particular for use in LNG ship-to-ship transfer.

Great potential
The FLNG sector has great potential – however, for this to be fully realised it is vital that suppliers act as true consultants and deliver the full value of their expertise as much as their products. Whether looking at seawater intake or LNG loading and offloading, fluid handling companies must act as advisors from the very beginning of a project and help ensure that the equipment selected can minimise risk and opex throughout the complete lifecycle of a project.

Vincent Lagarrigue, director of Trelleborg Oil and Marine
Vincent Lagarrigue, director of Trelleborg Oil and Marine