The Polyethylene Casing as Diffusion Barrier for Polyurethane Insulated District Heating Pipes

Abstract

Most district heating pipes are insulated with polyurethane foam in order to minimise heat losses. A high-density polyethylene (HDPE) casing protects the insulated pipe, and its permeability properties for the polyurethane cell gases, including air, play an important role for the long-term insulating capacity. The permeability of the HDPE casing of a district heating pipe was studied. Two methods were used to determine the permeability: I) by measuring the mass transfer through a sample, and II) by measuring the sorption and desorption of the gas in a sample. The experimental procedures are described. For carbon dioxide a permeability coefficient of about 9·10-16 mole·m-1·s-1·Pa-1 was found by both methods. For oxygen and nitrogen only method I was used and the permeability coefficients found were 1.9 and 0.6·10-16 mole·m-1·s-1·Pa-1, respectively.