When conveyants must be maintained at a specified temperature, steam jacketing is used frequently, often in lieu of electric tracing.
Traced assemblies are similar in concept to jacketed assemblies in that there is an inner, smaller diameter hose encased by a single large diameter hose. Where jacketed assemblies surround the media with heat or cold, traced assemblies have the media surround the hose containing the heating or cooling element. The tracer, or inner hose, may also be installed in a long 'U' shaped loop within the outer hose, with the steam inlet and outlet at the same end of the assembly.
Use of an external flexible armor protects metal hose from abuse due to rough handling, abrasion and bending below it's limits. Often a rubber cover can accomplish this as well as armor if temperatures will permit
If high conveyant velocities are required, use of an internal flexible metal liner will prevent damage and reduce abrasion problems.