GTT NO96: Why Insulation Must Carry Loads as Well as Keep LNG Cold

Inside an LNG tank, the metallic surface attracts attention. The less visible structure behind it explains much of how the system works. For an engineer, understanding containment begins with three connected questions: what retains the liquid, what limits heat transfer, and what supports the cargo loads?

GTT describes NO96 as a membrane system with primary and secondary Invar barriers, each 0.7 mm thick. Invar is an iron–nickel alloy containing 36% nickel. The insulation layers support the membranes; the primary membrane contains the cargo and the second provides a further liquid barrier in the event of primary leakage.^S1

The following is a conceptual ordering from cargo toward the inner hull. It is a teaching model, not a construction drawing. Corners, penetrations, joints and local support details are omitted.^S1S3S4

The term insulation assembly matters. It refers to the engineered combination of materials, geometry and interfaces, rather than assuming that every constituent has the same structural function.

Figure 1 — two engineering views of the same wall

The thermal task

Insulation reduces the rate at which heat reaches the cargo. Its performance helps determine the vapour quantity that the ship must manage, but heat transfer is not eliminated.^S2

Choi and colleagues measured thermal conductivity over a range extending from room to cryogenic temperatures and used those properties in insulation-box calculations. They also examined hull temperature in a scenario involving leakage through the secondary barrier. The abstract connects insulation assessment with the protection of the supporting steel structure, rather than treating evaporation as the only concern.^S10

The mechanical task

In the traditional box-based NO96 architecture, the plywood structure has an essential supporting role. The distinction is between the insulating medium and the engineered box assembly: saying that the insulation system carries loads should not imply that loose insulating fill alone forms the structural load path.^S1S5

At a conceptual level, pressure acts on the membrane, its backing supports that pressure, and forces pass through the supporting assembly toward the inner hull. The load distribution depends on the geometry and interfaces. The barrier sequence shown above is therefore a physical ordering, not a claim that every force travels through a single identical route.

Two possible structural responses help explain the distinction:

• Buckling: a supporting member loses stability under compression.
• Crushing: material or a component undergoes compressive failure.

Park’s 2019 study addresses crushing of horizontal members in box-type NO96. Its abstract describes small-scale tests and nonlinear finite-element calculations that also account for bending. Park and Lee’s 2018 work addresses buckling. They are separate investigations of different limit states.^S5S9

Research by Park and Lee investigates buckling capacity in box-type NO96 containment under sloshing loads, using finite-element calculations with temperature-dependent material considerations. Its abstract explicitly treats dynamic response as part of the strength assessment.^S5

Geometry, temperature and loading must be read together

Cha and colleagues tested MUF-resin plywood used in membrane-containment applications. Their experiments varied temperature, specimen thickness and loading direction. They reported changes in mechanical behaviour, including brittle fracture under specified cryogenic test conditions. The work demonstrates why room-temperature strength alone is an incomplete description of a material operating across a thermal gradient.^S6

Figure 2 — the material behind the structural question

What this changes in an engineering discussion

Sloshing assessment concerns more than describing the movement of liquid. DNV’s historical 2014 methodology overview links load assessment with containment strength and the supporting inner hull, including statistical treatment and model-test scaling. It is useful background, not a current class rulebook.^S4

For a box-based NO96 discussion, the Park and Lee study provides a focused example: buckling capacity is assessed against dynamic loading, rather than inferred from a thermal-performance number. Its relevance is the question being investigated: how the supported structure responds to the imposed loading.^S5

Service also matters. GTT explains that FSRU/FSU sloshing assessment considers filling levels, site conditions and mooring arrangements when selecting reinforcement. A system intended for one service cannot be assumed suitable for another simply because both carry the NO96 name.^S7

GTT’s family table distinguishes Perlite, GW, L03 and L03+. The first uses perlite; GW uses glass wool, while the later developments introduce foam into the arrangement. Identify the precise variant before describing its construction.^S1

NO96 Super+ retains the double Invar barriers but uses reinforced polyurethane foam panels in both insulation spaces, with glass-wool joints between neighbouring panels. GTT’s development description assigns these panels both insulating and membrane-support functions.^S2S3

Manufacturer reference BOR values

BOR means boil-off rate; the values below are expressed as percentage of cargo volume per day.^S1S2

Construction descriptions are deliberately at family level. L03 and L03+ require variant-specific drawings to establish the detailed allocation of boxes, panels and interfaces.^S1S2S3

The Super+ value is GTT’s stated guarantee for the identified reference design. These are manufacturer figures, with different reference capacities, not comparable measurements from five ships on the same voyage.^S1S2

For a meaningful comparison, ask:

• Are capacity, tank arrangement and reference conditions comparable?
• Is the number a design reference, contractual guarantee or measured result?
• How is gas generation matched to the ship’s consumers and recovery systems?
• What happens when generation and demand differ?
• Are cargo retention, auxiliary energy and emissions evaluated separately?

This is a framework for comparison, not a calculation of voyage savings. A lower published BOR does not by itself establish lower total fuel consumption, lower emissions or better structural reliability.

Related: explore indicative scenarios in the BOG & Propulsion Economics Calculator.

The following questions connect the design explanation with shipboard awareness. They are an engineering review framework, not operating sequences or alarm settings.

Know the installed configuration

Can the crew identify the containment variant and locate the approved descriptions of its spaces, insulation and support arrangement? Does the training material describe the actual ship, or only a generic NO96 tank?

Read temperature and pressure in context

Which measurements are available, where are they located and what is their intended purpose? Which trends require escalation under the vessel’s procedures? A single reading should not be presented in an educational article as proof of a particular failure mechanism.

Understand barrier-space monitoring

How are the interbarrier and insulation spaces identified on this vessel? Which gas-analysis, pressure and temperature records support an assessment? Public descriptions cannot supply the ship’s nitrogen-control settings or leak-response instructions.

Preserve the condition history

Which inspections, repairs and abnormal observations concern this installation? Are conclusions tied to the actual variant, component and evidence? Generic research should help frame a question, while acceptance and corrective action remain matters for the approved technical process.

Construction sources: S1–S3 and S8. The table explains differences; it does not rank operating reliability, maintenance cost or suitability for a particular trade.

Related: read the GTT Mark III, Flex and Flex+ article.

For engineers, the enduring questions are concrete: which variant, which component, which loading condition and which supporting evidence? Keeping those questions together is the foundation for an informed technical discussion.