Ship to ship transfer of LNG

Gutteling, a Dutch manufacturer of flexible composite hoses, and Exmar, a Belgium based shipping company that operates various LNG vessels, took the challenge to justify the safe and reliable operation of a hose system for offshore LNG transfer. TNO is appointed to define the qualification program for their system and to execute a complete test program.

Worlds  first STS LNG transfer - 2006, Gulf of Mexico- © Exmar – Gutteling B.V.
Worlds first STS LNG transfer - 2006, Gulf of Mexico- © Exmar – Gutteling B.V.

Vessels transport Natural Gas in liquid state (LNG) at cryogenic temperatures from the source to entrance points of gas distribution networks near to consumers. Therefore harbors have facilities to regasify LNG. Due to the high investments and safety issues related to building and operating such harbor LNG-terminal, for some areas LNG is regasified near shore on transport vessels equipped with regasification units. To expand this market and add flexibility to the supply chain it is preferred to operate conventional transport vessels and dedicated gasification vessels. This solution however requires offshore transfer of LNG from ship to ship. Until recently it was not possible to reliably transfer LNG which is typically done at 3 bar pressure and a temperature of -162°C.

Good design of flow systems is essential to prevent high maintenance cost, reduced safety, increased environmental pollution, excessive energy consumption and poor reliability. The qualification test program is based on the requirements of the guideline pr-EN1474-II, which will be released by the end of this year.

The qualification program

Though this standard EN-1474 specifies the baseline for qualification, many issues need to be detailed requiring breaking new grounds. Not only test methods need to be developed, but rules need to be interpreted and requirements have to be detailed.

Together with the complex behavior of the composite hose, this results in a challenging project that is much more than executing specified tests and comparing results to unambiguous requirements.

TNO proposed a multilevel test program combined with developing models that predicts the behavior of the hose system. Such approach provides a better understanding of the behavior of the hose system under all possible loading conditions and results thus in a higher confidence in the system. In addition, it potentially provides to Gutteling and Exmar a basis to qualify different hose configurations with a reduced program.

Full scale flow test for 8 inch multi composite hose with transducers.
Full scale flow test for 8 inch multi composite hose with transducers.

Multilevel test program

The program covers testing of the composing materials, tests at small hose assemblies (typical length 1 m) and tests on larger assemblies (typical 3 – 6 m) and a full scale test. Wherever possible tests are performed at a small scale. The larger the specimen the fewer tests are performed. The full scale test is performed on one sample. The bridge between each level is formed by predictive models. Moreover flow aspects and structural aspects like strength and fatigue are assessed integrally.

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ir. C.B.P.J. (Bas) van den Beemt
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LNG STS Qualification TNO 331 KB