PHPK Technologies : News and Events : Cryogenic and High Vacuum Equipment Piping Insulated Filters Assemblies Valves Cryocoolers Cryopumps Pumps vacuum insulated pipe


Vacuum Insulated Piping (VIP) has been widely used for over 40 years in cryogenic systems. Originally specified for only critical applications where maintaining a liquid state was absolutely imperative, the use of VIP has evolved into a long term economic means of transferring liquid cryogens in all related industries. Since vacuum insulation was first invented by Sir James Dewar in 1892 it has been used for insulating everything from sub-cooled liquid helium at near absolute zero to hot coffee in a Thermos bottle. The performance and economic advantages of vacuum insulation have been realized in many industries and applications for decades yet the LNG industry has been very slow to embrace this "new" technology. Extensive and unnecessary boil-off gas, pipeline insulation maintenance and repair, and running and maintaining large compressors and/or reliquefiers have been a common burden and expensive cost to LNG plant and terminal operation that has simply been accepted. Furthermore, when considering all aspects of the plant design and cost of using VIP versus mechanically insulated piping the initial capital investment can be lower with VIP. So why is VIP not more widely used and accepted in the LNG industry? With all the LNG Liquefaction facilities and regasification plants being built and planned only a very few are using VIP by only one EPC. Perhaps it is the perceived complexity of vacuum insulation or possibly that until recently there has been only one qualified supplier of large diameter, long length VIP with direct seaport access. Or maybe VIP is viewed as a "new" technology reserved for laboratories or other controlled environments. Whatever the reason(s) for VIP not being used in all LNG transfer applications the fact remains that manufacturing, installing and maintaining VIP for LNG industry applications is a far simpler and more economical than many people realize. A shop fabricated VIP pipe section or spool piece is simply constructed of an inner carrier pipe, normally stainless steel, which is wrapped with multiple, separated layers of a reflective material such as aluminized mylar to insulate from radiant heat transfer. A jacket pipe is centered over the carrier line, also stainless steel or a coated carbon steel material, using low heat conductive "spacers" and sealed at each end with a low heat conductive end closure. The jacket pipe also contains a convoluted "expansion joint" in each straight section to compensate for the contraction of the carrier pipe when LNG is being transferred. Each section has a chemical gettering system added to the vacuum space and then is	leak tested and evacuated to a level of 10-4 torr through an evacuation port on the jacket pipe. Although this may sound over simplified, for experienced manufacturers of vacuum insulated equipment and piping systems such as LINDE and PHPK Technologies, this is an every day process that we have performed and perfected over many years. As in any process piping system additional considerations must be taken into account and therefore a thorough analysis must be performed by the manufacture to assure the required extended life of the piping system. The installation of the VIP is also a simple process that can reduce construction time considerably. With prefabricated pipe sections, including elbows and tees, coming in lengths up to 30 metres the number of field welds can be reduced by more than 75% and each joint made in the field can either be mechanically insulated or vacuum jacketed in a matter of hours. The jacket pipe material is sufficient to support the weight of the spool so supports, guides and anchors are also simple and easy to install. Additionally the outside diameter of VIP is approximately 150mm less than the mechanically insulated pipe which can reduce the size and/or number of piping supports throughout the plant. The LINDE/PHPK team can also manufacture the VIP in prefabricated, self contained modules that include trusses, supports, expansion loops, and other process piping for spanning between jetty pilings. The heat leak performance of VIP is a minimum of one tenth that of mechanically insulated piping. This not only significantly reduces the boil-off gas (BOG) in a steady state operating condition but also results in much faster cool-down time and allows transfer of LNG over much greater distances. Less BOG in the piping transfer system can reduce the number and size of compressors or reliquefiers needed to keep pace with loading or off-loading operations at liquefaction and regasification facilities. This saves a tremendous amount of money in capital investment, maintenance costs and energy costs throughout the life of the plant. Maintenance of VIP is also a strong point when compared to mechanically insulated piping. Once a VIP system is installed and operational it can remain maintenance free for many years. Mechanically insulated pipe is prone to loss of its vapor barrier causing moisture and ice to build up and deteriorate the insulation resulting in an increased heat leak and more BOG. Maintaining a large mechanically insulated system sometimes requires a full time crew.
New Innovations: LINDE/PHPK has recently introduced to the LNG Industry the Vacuum Insulated Thermal Compensation Guide (TC Guide). The LINDE/PHPK Thermal Compensation Guide is a durable and economical way to compensate for thermal contraction and cycling in any cryogenic piping system. Comprised of two internal hinged joints in a single vacuum jacketed spool section, the TC Guide will allow up to 4 ½ degrees of deflection (9 degrees when installed in a reverse deflection) with virtually no stress on the elbows. This technology has also been around for many years and has been used extensively with great success in the Aerospace Industry by NASA and other US government contractors. The use of TC Guide spools can greatly reduce or eliminate the need for costly expansion loops in any LNG piping system. In a typical large diameter LNG piping system the TC Guide spool can allow for nearly four times the offset movement of a conventional rigid pipe expansion loop. This would allow for spacing of expansion loops on a straight piping run to be increased by more than three times the distance. Also, for configurations that have	a natural change of direction and/or branches the use of TC Guides can allow for a simpler routing design and reduced nozzle stresses on connecting equipment. In addition to reducing the costs of expensive expansion loops the TC Guide will reduce the overall system pressure drop. This would allow for a lower initial loading or offloading pressure of the LNG which will result in less flashing of LNG to gas due to the lower amount of pressure drop. In some systems the reduced pressure drop also allowed for a reduction in carrier line size. In one particular sample case, use of TC Guide spools in an actual LNG import terminal where two parallel 30" LNG transfer lines were running over two kilometers each, the use of TC Guide spools would eliminate 12 expansion loops with a total of 92 elbows and 850 metres of piping. In addition to eliminating the piping materials, labor and associated supports, the overall pressure drop for each 30" line was reduced by over 25% at a transfer rate of 30,000 GPM.