Measurements on the cell gas composition of old district heating pipes insulated with carbon dioxide-blown polyurethane foam and still in use, are reported. The pipes had been in use for up to more than eight years at the latest date of measurement. The effective permeability coefficients for carbon dioxide in the district heating pipes at room temperature were calculated to be in the range 1.5 to 5.3·10−16 mole m−1·s−1·Pa·−1. For carbon dioxide, the major part of the resistance to diffusion was found in the polyethylene casing. The influence of the dimension of the district heating pipe and the temperature of the polyethylene casing is discussed.
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