Liquefied natural gas (LNG)

Gas as an energy/heating source is a need in many countries. The distance between the gas fields and the final user is generally large. This makes transport through pipe lines unpractical and cost inefficient.

Transportation by car, train or ship, requires that the gas is cooled down to minus 162 °C. This transforms the gas into liquid with a volume which is 1/600 of the original gas volume. The volume reduction makes transport by, for instance, ships possible. Special designed LNG ships are made for this purpose. After arrival to the destination / port, the LNG is heated and hence transformed into gas, which is delivered to the gas customers through local pipe lines.

Natural gas

Natural gas may be present as dry gas, wet gas and LNG. Natural gas is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the earth throughout millions of years. The gas may be composed of several chemical components with different characteristics. Most of the compositions are composed of hydrogen and carbon atoms. Therefore they are called hydrocarbons.

Dry gas

Dry gas means gas that does not contain liquid components at atmospheric temperature and pressure. Mainly it consists of methane, but often also of ethane and smaller amounts of heavier hydrocarbons, and carbon dioxide (CO2). Such gas is also called sales gas and is transported in pipe lines to the customers.

Wet gas

Wet gas consists of both dry gas liquid phase hydrocarbons, as ethane, propane, butane and heavier. By atmospheric temperature and pressure the wet gas is partly liquid and partly gas. Dry gas is achieved by separating the liquid phase from the gas phase. The gas phase is then sold as pure components (methane, ethane, propane, butane).

LNG

LNG is an abbreviation for Liquefied Natural Gas, which means natural gas made liquid by cooling down to minus 162 Deg C. Usually transport to the customers is carried out by ship.

Due to the characteristics of facilities containing LNG, special care must be taken into account when working with insulation systems for the LNG- piping, containers and equipment. With regard to design, the following aspect is important to consider in this connection.

Compressive strength

It is important to choose insulation materials with high compressive strength, as building and maintenance often is carried out adjacent to, or directly on the existing insulation. Insulation damage due to stepping is therefore likely to occur. Such mechanical damage can be avoided by using insulation materials with high compressive strength and with the ability to absorb point load, caused for instance by steps. In addition, a high compressive strength is required for pipe supports, as the weight load may damage the insulation in areas with the need for pipe support.

Flammability

Fire protection is often required for LNG insulation systems. The materials, including caps/jacketing and tension straps shall be fire classified. The cap/jacketing and the tension straps shall be made of stainless steel.

Additional materials

It is important to use correct additional material for LNG insulation. Because LNG insulation is critical and costly, all additional material must be tested and documented, so that specified requirements are met.

Intrusion of humidity

To prevent intrusion of humidity, a vapour barrier is generally included in an insulation system. This is crucial for LNG insulation. Intrusion of humidity into a cold insulation system will cause icing and hence risk of damage to the insulation system. A cold insulation system, which is not diffusion tight, therefore requires a vapour barrier. Vapour barrier materials have high diffusion resistance. The vapour barrier shall be installed at the warm side of the insulation system.

For long term operation it is important that the vapour barrier is correctly installed. If, for instance, 1 volume % of humidity is added to mineral wool, the thermal conductivity of the mineral wool will increase with approximately 20 volume %. If 5 volume % humidity is added to a material with closed cells, the thermal conductivity will increase with approximately 5 volume % .

This is especially important to have in mind for insulation systems to be installed on pipes containing cryogenic liquids.

A cryogenic liquid is defined as a liquid with a boiling point below -90˚C.

Argon, Helium, Hydrogen, Nitrogen and Oxygen are the most common industrial gasses that are being transported and stored at cryogenic temperatures.

The use of diffusion tight insulation types as cellular glass, plastic or aluminum foils are commonly used, but it is the the workmanship that is most important for the quality of the final insulation system.

Moisture barriers often consist of mastics based on plastic or asphalt. Plastic laminated barriers and metal foils are also used. Some insulation products are delivered with attached moisture barrier.

A cap /jacket on top of a diffusion tight material does not always indicate that a moisture barrier is established, as possible movements of the cap/jacket may cause the joints to crack.

Cellular rubber has some diffusion resistance, and is often installed without an extra moisture barrier on cold piping and equipment.

Cellular glass is diffusion tight, but the joints represent a weakness in that respect.

Icing

Intrusion of humidity/water in the insulation, followed by icing, reduces the insulation capacity and hence increases the operational costs. Icing may be a result of a defect vapour barrier or insufficient insulation thickness. The ice weight may cause damage to the insulated equipment if it exceeds its load capacity.

Pipe supports

Pipe supports must be properly insulated to prevent thermal bridges and the formation of ice, and must be able to withstand movements as contractions at start up of the pipe system. A relative short part of a LNG pipeline may contract up to 2 - 3 cm.

Fire risk

LNG always represents a risk of fire. Offshore installations and Floating Production, Storage and Offloading (FPSO) units are especially exposed. It will always be required that the insulation systems of such facilities is able to withstand the fire loads that possibly may occur.

The insulation system must be constructed so that the outermost layer has the necessary fire capacities. Stainless steels, most often with 0,7 to 0,9 mm thickness, are typically used for cap/jacketing.

The insulation materials meant for LNG facilities should have the following characteristics:

• Low thermal conductivity
• Ability to carry loads
• Ability to resist mechanical damage.
• Low weight
• Unaffacted by vapour / humidity

Commonly used materials

Newer systems, also used

• Cabot, aerogel beads (Nanogel®)
• Aspen Aerogels, aerogel blankets
• (Pyrogel® and Spaceloft®)
• Sordal, polyimide foams (SOLREX®)
• Inspec Foams, polyimide foams (SOLIMIDE®)
• TAI, pipe insulation panels
• NASA, Layered Composite Insulation (LCI)
• NO
• MARK III

To illustrate typical LNG insulation systems and solutions, the two most frequently used insulation systems is discussed below.

To meet the special LNG insulation requirements, cellular glass is a convenient alternative. There are several reasons for why. One of the reasons is that cellular glass insulation is a “foam” of sodium silicate with impenetrable cell walls, an important aspect with regard to the risk of vapour/humidity intrusion in the insulation system.

As mentioned earlier, the pipes being used in LNG facilities, contract at start up of the facilities. Thermal expansion occurs when a material change its volume due to temperature change. Since the thermal expansion coefficient for cellular glass is about the same as for steel, the cellular glass will contract about the same as the steel pipe.

Figure below shows cellular glass, installed as ground cover inside a huge storing tank.

A typical build up of the bottom of an insulation system based on cellular glass, is three layers of 20 cm thick load-bearing cellular glass insulation blocks with a bituminous membrane between the layers of insulation and at top and bottom of the insulation system. After installation of the final layer of insulation, a layer of fire sand is added on top of the insulation system before installing the bottom plates. The sand protects the insulation system during the welding operation of the the bottom plates.

When cellular glass insulation is used for LNG facilities, a typical procedure is to use two layers cellular glass. It is important that the insulation work follow the build up of cold insulation. Care must be taken when mounting the cap /jacketing at the outside of the insulation system. To avoid possible puncturing of the vapour barrier, caused by screws and pop rivets, an extra layer of insulation between the vapour barrier and the cap / jacketing is recommended. Drainage shall not be installed in LNG insulation systems, due to the risk of thermal bridges and ice formation.

The build up of a two-layer insulation system shall provide that all joints in the second layer are shifted compared to the joints in the first layer.

It is important to mount the vapour barrier (vapour stop) correctly. If it is not tight, condensation and icing is a probable result. The ice will damage the isolation.

Pipe supports are another critical aspect in piping systems.

Mounting details of a layer of insulation on pipes

By insulating LNG pipes and tanks, or by cold insulation in general, it is of high importance to secure that all the insulation is tight and that the vapour barrier is correctly mounted.

At temperatures down to -167°C LNG insulation problems may be expensive and dangerous. Accuracy during mounting is crucial, and even small deviations may cause great problems at start up of the LNG facilities. It is challenging to shut down the facilities for repair works.

Nowadays most of the insulation work of pipes and tanks is usually carried out outside the LNG facilities. Lower costs is the reason for this practice. However, poor insulation workmanship may be experienced, because the insulation entrepreneurs sometimes lack the proper competence. It is therefore of high importance that the customer carries out frequent inspections during mounting of LNG insulation systems.

The following photos, show some typical defects observed during an inspection.

Space between piping and insulation must be avoided

Space through the insulation. Risk of icing

Hole in the vapour barrier (bolt) Risk of icing

Large holes in the insulation

Large opening in the insulation

Conclusion

A daily independent inspection and follow up at the construction site (for instance carried out by a FROSIO inspector) may contribute to problem prevention and cost savings.

Cryogel® Z is a flexible material,p which gives a minimum of weight and thickness. It is a convenient insulation material for LNG facilities. It is available in two thicknesses with an integration of a vapor barrier, preventing intrusion of humidity.

The flexibility and the very low thermal conductivity of Cryogel Z eliminates the need of complex and expensive need for expansion joints and simplifies the installation work. In addition to the cold insulation capacity, Cryogel Z has beneficial acoustic and fire engineering characteristics.

Process temperature: -162 °C
Insulation system: 2 lag (20mm) Cryogel-Z over PIR

International  standards used fir insulation of LNG systems.

ASTM Standards

• ASTM C552 Standard Specification for Cellular Glass Thermal Insulation
• ASTM C795 Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel
• ASTM C1639 Standard Specification for Fabrication of Cellular Glass Pipe insulation
• ASTM C1729 Standard Specification for Aluminum Jacketing for Insulation
• ASTM C1767 Standard Specification for Stainless Steel Jacketing for Insulation
• ASTM E136 Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C

EN Standards

• EN 1473 Installation and equipment for liquefied natural gas. Design of onshore installations
• EN 13468, Thermal insulating products for building equipment and industrial installations
• EN 14305, Thermal insulation products for building, equipment and industrial installations. Factory made cellular glass (CG) products.
• EN ISO 1182, Reaction to fire tests for building products — Non-combustibility test

International Organization for Standardization (ISO)

• ISO 9001: Quality management systems — Requirements
• ISO 9002: Quality systems. Modelled for quality assurance in production, installation, and service

United States Coast Guard International Maritime Organization

• Coast Guard Approval Number: 164.109/55/0

British Standards (BS)

• BS 4370-1-4 Method of test for rigid cellular materials

German Standards (DIN)

• DIN 4102-1 Fire Behavior of Building Materials and Building Components.