Mitsubishi Heavy Industries, Ltd. (MHI) has completed development related to floating production, storage and offloading units for liquefied natural gas (LNG-FPSO), and has obtained two kinds of approval in principle (AIP) from major international ship classification societies. In tandem with intensified activity in medium- and small-scale offshore gas field development, demand for LNG-FPSOs, a new method of gas production offering movable capability, has been increasing globally. Boosted by the new recognition of the safety and reliability of its proposed units, MHI will now begin aggressive marketing activities toward construction of the world's first LNG-FPSO.

The first AIP is for an LNG-FPSO concept that adopts MOSS type spherical storage tanks, whose safety and reliability have already been confirmed through wide use in LNG carriers; it was obtained from Lloyd's Register of Shipping (LRS) of the UK. MHI plans to propose LNG-FPSOs incorporating the MOSS type tanks to medium-scale gas-field development projects with 1 to 2 million tons per annum (MTPA) production capacity, a sector where large demand is expected.

The MOSS type tank has been generally considered unsuitable for LNG-FPSOs due to its hemispherical shaped dome, which impedes providing enough space for the topside plant on the deck. MHI has solved this problem by enlarging the tank size and reducing the number of tanks required so that enough flat deck space for the topside plant can be secured.

The other API is for an independent prismatic tank categorized as International Maritime Organization (IMO) Type B*1, which satisfies international rules applied to gas carriers (IMO Gas Code); it was obtained from three classification societies: LRS, American Bureau of Shipping (ABS) and Nippon Kaiji Kyokai (ClassNK) of Japan. MHI expects solid demand for this type of LNG-FPSO mainly for gas fields with more than 3 MTPA production capacity. Although the independent prismatic tank type B LNG-FPSO is considered costly than the MOSS type or membrane type, in which the ship hull itself functions as the tank's supporting structure, it is capable of providing more deck space for the topside plant than the MOSS type. Like the MOSS type, independent prismatic tank type B is free from possible liquid sloshing inside the tank, a potential problem with membrane type tanks, where impact pressure can generate liquid motion, or traveling waves, inside the tank, resulting in the damages to the tank.

An FPSO is a floating unit equipped with facilities for production, storage and offloading of oil and gas. Although oil FPSOs have already been built and delivered by MHI and other companies, winning solid acclaim for their reusability due to their ability to be moved from one oil field to another, to date the construction of LNG-FPSOs has remained in the planning stage.

Generally, LNG has been produced from large-scale gas fields on land or near shore and production has been handled by a gas liquefaction facility on land. However, as the development of such gas fields approaches the saturation level, development of large-scale sea-bottom offshore gas fields and small- and medium-scale offshore gas fields has been drawing attention. "Stranded" gas reserves, i.e. natural gas fields that have been discovered but remain untapped, are said to account for 40 to 60% of confirmed recoverable gas reserves, and it is for this reason that the LNG-FPSO has come into the spotlight.

Leveraging its expertise garnered through its experience in constructing oil FPSOs, numerous LNG carriers and offshore structures, and boosted by collaboration with BW Offshore Limited, one of the world's leading FPSO contractors, for the MOSS type LNG-FPSO, MHI will actively engage in business expansion in the ocean resource development and exploration field, especially LNG-FPSOs including the larger size ones utilizing independent prismatic tank type B as well.

Note: IMO Type B: According to the rules of the International Maritime Organization (IMO), a gas carrier's independent tanks must be of one of three types -- Type A: tanks which are designed primarily using recognized standards of classical ship-structure analysis procedures; Type B: tanks designed using model tests, refined analytical tools and analysis methods to determine stress levels, fatigue and crack propagation characteristics; or Type C: tanks which meet pressure vessel criteria.