Introduction to Vacuum Insulated Piping (VIP) for LNG Service

History of Vacuum Insulated Pipe

VIP has been manufactured for over 45 years as a low heat leak transfer system for many cryogenic fluids. The primary fluid that required the development of VIP was liquid helium. This is the coldest cryogenic fluid at -269°C (-452° F) and has a very low latent heat of vaporization of about 9 BTU/lb. With this low latent heat of vaporization it is impossible to transfer this liquid from one point to another with standard mechanically insulated pipe systems. Liquid helium will boil almost immediately upon entering anything less than a vacuum insulated piping systems. VIP was developed in the early 1950;s by Ohio State University Dr. Herrick L. Johnson predecessor of CVI (now Chart Industries) for transferring of these cryogenic fluids.

Industrial gas suppliers, national laboratories, aerospace companies, NASA, medical facilities, food processing operations, fuel facilities and the entertainment industry have used VIP extensively since that time for cryogenic fluids including liquid nitrogen, liquid oxygen, liquid hydrogen, liquid helium, and liquid methane (LNG).

Hydrocarbon Market

VIP was first used in a LNG production facility in 1998 in Trinidad, Atlantic LNG Train 1 facility. This was a 4" ship cool down line that was about 760 meters long. This proved very successful and is still operational today with no degradation in performance or maintenance requirements. The time to install this entire line ready for LNG operation was less than one week. This product is now being used in other LNG receiving and sending terminals. Some of the terminals include, Distrigas in Everett, MA, Egypt LNG at Idku and Darwin LNG in Australia. Atlantic LNG has added additional VIP to the Train 4 operation in Trinidad. Sizes that are now being built include 1" through 30" VIP.

Advantages of VIP

There are several advantages for using VIP in lieu of other insulation methods that will be discussed in this section including the present insulation methods used before the introduction of VIP for LNG terminals.

   LNG Mechanically Insulated Pipe Systems

Historically, LNG terminals field fabricate all cryogenic piping and then insulate the piping with polyurethane foam, foam glass or other mechanical insulation material. The thickness of this insulation varies from 6" to 12" depending on the pipe size and the client's requirements and insulation type. This insulation is installed in all types of environments near the water that makes it very difficult to control the quality of installation and contamination most generally occurs. The support system for the piping using mechanical insulation is expensive using cold shoes and increases the heat leak into the piping as well as being difficult to seal the vapor barrier at these supports. Over time mechanical insulation degrades and the vapor barrier allows moisture into the insulation space that eventually destroys this insulation and it must be replaced. This degradation is very critical in sending terminals where all vapor is re-condensed and initial sizing of these re-condensers is based on certain insulation values for the piping system. It is also critical in receiving terminal for safety and reduces maintenance and operational costs.

   VIP for LNG Terminals

The following is a list of items that should be reviewed as a benefit to the end user as well as to the EPC selected for installing LNG piping in terminal applications.

• VIP is factory fabricated, currently in spools up to 30 meters long, in all sizes specified for the terminal and the fabrication can be done concurrent with other operations such as LNG tank erection, jetty construction, pipe rack fabrication, etc. being completed on-site.
• VIP minimizes the number of field joints which will reduce time and cost to install LNG transfer piping.
• Field testing is reduced to radiographing one joint every ~30 meters or dye penetrant testing the joint if bayonets are used.
• Heat leak of VIP is in the order of 10 times less than all known mechanical insulated systems. The best mechanically insulated system had a heat leak of about 8 BTU/hr-ft2 (25.2W/m2) and VIP average heat leak is 0.8 BTU/hr-ft2 (2.52 W/m2).
• Reduced heat leak in VIP reduces the size of re-condenser required at sending terminals.
• Reduced heat leak also allows you to run VIP ten times further than can be achieved with mechanically insulated pipe.
• Less time and energy is required to cool down VIP because there is no mechanical insulation to cool down.
• Bowing during cool down is mitigated with VIP due to the lower heat leak and uniform temperature from top to bottom of the pipe.
• VIP thermal performance will not degrade with time as does mechanical insulation.
• No expansion loops are required when using the Chart Patented internal bellows design. This allows the pipe to be run in a straight line to further reduce heat leak, pressure loss and cost.
• No cold shoes are required since the vacuum jacket is supporting the inner pipe
• Support system costs are reduced to using carbon steel since the vacuum jacket is always at ambient temperature.
• The larger diameter jacket acts as a strong back for the inner process piping allowing grater span between supports. In most cases the supports for the piping can be reduced in half if VIP is the only piping on the rack.
• VIP will last the life of the plant with little or no maintenance or degradation of operation over a 30 year period of time.
• The vacuum jacket is either stainless steel or carbon steel and protects the inner process pipe from physical damage.
• The shop fabrication of VIP assures a clean high quality product that will arrive at the site ready to install.
• Installation of VIP will take only about 10 percent of the time that is required mechanically insulated pipe. This advantage allows earlier star up and on-line operation.
• VIP takes up less space than other insulation methods. VIP requires only 2-3" of insulation space around the core pipe for the jacket. An example of 309" diameter pipe will have a 36" diameter jacket. The 3" annular space applies to all pipe sizes.
• All VIP for LNG service is fabricated in Chart's facility in New Iberia, LA with access to the inter-coastal waterway for shipping by barge or ship to ports worldwide.
• The advantages of VIP will make a LNG sending or receiving terminal a higher performing, lower maintenance and safer operating facility. Each terminal has different requirements and will conform to all other safety requirements.

Vacuum Jacketed Pipe Components

All vacuum insulated piping consists of several items that will be described briefly below for overall information so you can better understand this highly efficient insulated piping system.

   Inner Line or LNG Carrier Pipe
The inner pipe is designed in accordance with the customer specifications for the fluid pressure, temperature flow rates In most cases it will comply with ASME B31.3 and NFPA 59A including any other customer specifications. The typical material is ASTM A312, 304/304L stainless steel.

   Jacket Pipe
The jacket pipe will typically be six inches larger in diameter than the carrier pipe. This pipe can be fabricated from carbon steel or stainless steel material and coated to the customer's specifications.

   End Connections
The vacuum insulated pipe will be supplied with long heat path end connections to reduce conductive heat transfer from the inner LNG pipe to the ambient temperature jacket pipe. There are several types of end connections.

• Male and female bayonet connections are presently available for pipe sizes 12" NPS pipe and below. Each application will be reviewed to see if bayonets will meet all design and pressure requirements. The advantage of the bayonet connection is that if further reduces field installation time by requiring a field weld only at each spool connections

• Vacuum insulated field joints are required for pipe sizes above 12" NPS pipe or when the system pressure requirement exceeds the bayonet rating. This joint consists of a butt weld inner pipe connection, insulating and welding a closure over this inner pipe connection and field evacuating this joint. This will take more time to complete in the field versus the bayonet connection but here is only one joint every ~30 meters.

• The field joint may also be mechanically insulated.

   Expansion Joints
Each shop fabricated vacuum insulated pipe spool will be supplied with an expansion joint designed for the thermal contraction of the inner line when it is cooled with LNG The expansion joints may be installed in either the inner or jacket pipe. If installed in the inner pipe the expansion joint is configured in a manner that has the LNG process line pressure on the outside surface of the bellows and the vacuum on the inside surface. Either way the expansion will contract when the inner line is cooled. A Chart patented secondary seal or controlled leak is also provided as part of this expansion joint assembly.

   Vacuum Pump Out Valve
In order to evacuate the annular space a pump out valve is provided on each pipe spool assembly. This valve has an elastomer o-ring for sealing the vacuum in each pipe spool. This valve normally has a vacuum gauge tube provision supplied for monitoring the vacuum space during shop testing, shipping and installation. This vacuum gauge tube is isolated from the vacuum space except when readings are taken.

   Radiation Shielding
The inner line is wrapped with a multi-layer insulation prior to installing in the jacket pipe. This will reduce the radiation heat transfer into the LNG to a very low level. The amount of layers used is based on the fluid temperature in the process line. For LNG applications, typically 16 layers are applied.

Type or Applications using VIP

Vip has a greater diversity than standard mechanically insulated piping and can be used in some applications where mechanically insulated piping can't be used. VIP applications include sub-sea VIP, Underground VIP, and vertical risers up the side of storage tanks. We have presently supplied LNG VIP for underground applications, vertical tank risers and standard above ground piping.

References

Chart has over 45 years of references for VIP and approximately 7 years of references exclusively in applications at LNG terminals.