| 摘要 |
<p>A double-walled pipe, especially for underwater petroleum pipelines, has a self-supporting sheet (7-9) of open-pore microporous material with sufficient flexibility to be wound around the inner pipe (1) in a sealed annular space (5) between the inner and outer pipes (1, 2). A free passageway is left beyond the material, preferably as an annular layer between the sheet and the internal wall of the outer pipe (2), for longitudinal gas circulation to create a reduced pressure (preferably of 0.5-100 mbars) along the annular space. Also claimed is a method of using the above pipe by varying the pressure in the annular space, during the life of a pipeline formed by the pipe, between a level of up to 50 bars and a level of 1-900 mbars for varying the overall thermal insulation coefficient in the range 0.5-5 W/m2.[deg]C between the pipe interior and exterior, the microporous material sheet being 10-14 mm thick and the gas circulation layer having an average thickness of 1-5 mm.</p> |
