rørirør

Rör i rör, or coaxial piping, is a pipe-in-pipe arrangement in which a smaller inner tube runs concentrically inside a larger outer tube, forming an annular space. This enables an inner fluid to be carried while the annulus acts as a jacket, insulation, or secondary flow path.

Variants range from non-insulated coaxial lines to insulated or vacuum-insulated configurations. In insulation versions the annulus contains insulation or is evacuated to minimize heat transfer. Joints are typically welded or flanged, and the assembly requires careful alignment and support.

Applications include cryogenic transfer lines, district heating or cooling networks with supply and return in one unit, chemical processing where leak containment and purge capability are desirable, and certain heat-exchanger or solar thermal systems.

Advantages include reduced heat loss, compact routing, and integrated containment; disadvantages include higher cost, greater fabrication complexity, and potential moisture or contaminant buildup in the annulus if seals are compromised.

Materials vary with service, typically steel or stainless steel for both pipes, with insulation types such as mineral wool, polyurethane, or aerogel. Design follows applicable piping codes and standards, focusing on concentricity, expansion allowances, valve interfaces, and leak/pressure integrity.