(Sorry if this was discussed before)
I open this thread because I recently learned that we have route=pipeline
relations. The wiki (1) seems to say that one can expect that the members of
such a relation are pipelines. On the other hand, I find relations with
members that are fences around pipeline=valve nodes or substations, in other
words, objetcs which somehow build the infrastructure of the pipeline. The
general wiki (2) about route relations says
"For pipelines, pipeline markers, and pipeline stations."
I also noted that some use roles like pipeline or substation, some don't.