| 摘要 |
<p>To produce a more flexible heat- insulated conduit, consisting of two concentric pipes 1, 3, of which at least the outer pipe is a corrugated metal pipe, a heat-insulation layer 2 of foamed plastics based on polyurethane is situated between the pipes, the polyurethane foam having closed pores and an elongation at break of at least 25%. Further, the wall thickness S of the heat- insulating layer 2 is less than 30% of the average diameter D of the outer pipe, the corrugated depth t of the outer pipe 3 is greater than 0.05 D and the distance a between two corrugation crests of the outer pipe 3 is smaller than three times the value of the corrugated depth t. The wall thickness (s, Fig. 2 not shown) of the outer pipe 3 is smaller than 0.2 times the value of the corrugated depth t. A plastics jacket 4, helical spacer 6 and a bituminous layer 5 are also provided. Figs. 5 and 6 (not shown) illustrate terminal and through connections which involve the use of a helical spring (9) to achieve a connection for the outer pipe 3 and brazing at a connection 10 or 15 to join the inner pipes. <IMAGE></p> |
