AN INSULATED FLUID DUCT

摘要

A duct or duct section (1) comprises an inner pipe (3) for conveying a fluid such as steam generated by a steam plant and an outer pipe (2) enclosing the inner pipe (3). There is a vacuum in the space (4) between the inner pipe (3) and the outer pipe (2) to provide thermal insulation for the inner pipe (3). With this arrangement, there is no need to provide thermal insulation material around the outer pipe (2) and so the duct or duct section is suitable for use in clean environments. An indicator (12) is provided on the outer pipe (2) to indicate failure of the vacuum in the space (4). The indicator may comprise a coating of a heat sensitive material which changes appearance, for example by changing colour, in the event of a rise in the temperature of the outer pipe caused by failure of the vacuum.