The SCAF pipeline encountered by Isaac Clarke and John Carver following their crash-landing on Tau Volantis was (presumably) one of many constructed by the SCAF on Tau Volantis to supply Facility One.
The pipeline is supported by large square stands attached to the ground with large bolts. It appears wide enough for a tram to drive through. On top and below of the pipeline are numerous habitation quarters, presumably for guards and workcrews maintaining the pipeline. Generators in the rooms power equipment, heaters and lights. Lifts and ladders provide access to the top of the pipeline, sections of which are covered with catawalks.
Due to 200 years of exposure to the elements, the pipeline has broken apart in many places and is no longer filled with anything (it is unknown what the pipeline was used to transport, but the design is similar to that of oil pipelines).