Cellular Insulating Materials for Pipelines Carrying Liquefied Natural Gas

Abstract

More detailed development of equipment designs for liquefied natural gas (LNG) and, among other things, pipelines for its transport is required in connection with expansion of the production of LNG in Russia and growth of the gas business. Pipeline design is determined by the type of insulation employed. Essentially all existing forms of low-temperature insulation for LNG equipment are described in the technical literature. Technical production, operational, and cost requirements for insulating material, which are inconsistent one with the other, however, make it very difficult to prioritize one form over the others. The following cellular materials have come into widespread use and are considered more promising: synthetic foam rubbers, foamglass, and foam plastics, which possess a closed-cell structure; this reduces migration of water vapor into the internal spaces of the insulated articles. Foamglass and foam plastics are distinguished by a rigid structure; this simplifies the creation of vapor barriers and the installation of a jacket. Incombustibility in air is a critical requirement for the insulating materials. In terms of chemical composition, foamglass is an incombustible material. Many forms of synthetic foam rubbers and foam plastics are becoming fire-resistant owning to the introduction of special additives. Comparison of characteristics of different forms of cellular materials for the insulation of LNG pipelines is of interest. The construction of an insulated LNG pipeline is shown schematically in Fig. 1. The pipeline is insulated by three layers of cellular insulation (foamglass or foam plastic). During production, the insulation is formed into shells, and is assembled by securing shell segments onto the pipeline, or on previous layers of insulation. The shells have a tolerance (not shown in the fi gure), which compensates for shrinkage of the insulation during freezing. The pipeline possesses thermal-shrinkage joints, and longitudinal and transverse vapor barriers. The latter are required to prevent migration of moisture through the longitudinal faces of the shells. An overflow opening exists in the lower portion of the jacket for extremely humid atmospheric air. Table 1 presents characteristics of various forms of cellular materials as applies to the pipeline design under consideration. Also shown for comparison are characteristics of the synthetic Armaflex rubber produced by the Armstrong Co. [1], the insulating technology of which differs somewhat from that shown in the figure. The Kingspan Niflam material is a product of Kingspan Industrial Insulation Ltd. (Great Britain), and in terms of chemical composition, is a polyisocyanurate containing basic properties of foam polyurethanes, but characterized by a lower combustibility. The Kingspan Niflam material has been used on a number of large-scale projects for the insulation of LNG equipment and pipelines. Requirements for the insulation procedure and construction of the insulation using rigid foams as the basic insulating material are as follows: