LNG Tanks: Composite Barriers

Natural gas accounts for a large proportion of our energy consumption (1). In the U.S., natural gas accounts for 34% of energy consumption, almost on par with petroleum (2). Cooled to about -270°F (-160°C), natural gas shrinks to approximately 600 times its normal size. Thus, it is easier to store and transport via marine shipments.

Ever since the Methane Princess delivered its first commercial cargo in October 1964, manufacturers and shipbuilders have scrambled to build larger LNG (Liquefied Natural Gas) tankers, with some tankers reaching capacities of 267,000 m3 - ten times those of the Methane Princess (3).

As the worldwide trade in LNG intensifies, equipment manufacturers and shipbuilders are naturally concerned about containment systems for LNG tanks (4). To ensure LNG is transported safely and efficiently, manufacturers need new technologies, such as composite barriers for LNG tanks. Composite barriers are an ideal lightweight composite solution for the oil and gas industry.

Types of LNG Tanks

There is a wide variety in the design and operation of gas carriers according to the type of cargo they carry (5). The International Maritime Organization defines five main cargo containment systems: integral tanks, membrane tanks, semi-membrane tanks, independent tanks, and internal insulation tanks (6).

Independent tanks are self-supporting and do not form part of the ship's hull (7). There are three basic designs - Type A, Type B, and Type C.

About 360 tankers have been certified to transport LNG gas to date. LNG is natural gas that has been cryogenically cooled to -270°F (-160°C), so it's easier to transport and store (8). It is primarily composed of methane but can contain up to 10% ethane and propane.

LNG tanks need to bear high pressures while maintaining low inner temperatures. In this instance, lightweight composite barriers provide high-performance tensile and thermal capabilities.

Type A Tanks

Type A tanks are non-pressurized and operate at near atmospheric pressure. They're prismatic and shaped from flat surfaces. Originally designed to carry liquid petroleum gas, they have also been approved for LNG transport. Type A tanks are not resistant to the propagation of cracks. Since LNG needs to be cooled to -160°C, a complete secondary barrier surrounds the tank with insulating material. This presents a prime area of consideration for composite barriers.

Type B Tanks

Type B tanks are spherical (Kvaerner Moss) or prismatic (IHI SPB) in shape (9). They are also non-pressurized. A drip tray forms a partial secondary barrier. This is designed to detect leaks long before the tank experiences complete failure. Again, this is an area of consideration for composite barriers.

Type C Tanks

Type C tanks are partially or fully pressurized. They're cylindrical, bi-lobe, or tri-lobe in shape. Because of the limited risk of structural failure, Type C tanks do not require a secondary barrier.

Composite Barriers in LNG tanks

Despite a lag in commonly agreed standards, the global composites industry is a $25 billion burgeoning market (10,11). With a wide range of applications in oil and gas, lightweight composites in the form of composite barriers are the ideal solution for the safe operation of LNG tanks (12).

ECTFE film is made from ethylene-chlorotrifluoroethylene resin. ECTFE is a partially fluorinated polymer designed to provide chemical resistance in corrosion-heavy environments. Composite barriers fabricated from ECTFE display the outstanding characteristics of fluoropolymer film.

ECTFE composite barriers retain their properties well below the -160°C required for transporting LNG, operating from -200°C (-328°F) to 165°C (330°F). Composite barriers from ECTFE also have low surface energy, allowing excellent self-cleaning capabilities. The high resistance to abrasion of composite barriers makes them ideal for insulating methane-rich environments.

Additionally, LNG hoses support the operational rigors of bunkering and LNG transfers. Ultra-high molecular weight polyethylene (UHMW-PE) films operate at ultra-low temperatures with continuous service temperatures rising to 200°C (392°F). The size and chemical stability of polyethylene molecules imbue UHMW-PE films with a low coefficient of friction and excellent resistance to a wide variety of chemicals and solvents. UHMW-PE composite barriers are ideal for the safe completion of LNG transfers.

Overall, composite barriers are an excellent lightweight composite solution for varied oil and gas applications.

Saint-Gobain's ECTFE film's excellent electrical, thermal, and mechanical properties make it ideal for composite barriers in LNG tanks. For more information, take a look at our barrier films page.

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