riser pipe vs riser main

riser pipe and riser main both are nouns.

Word	Noun	Adjective	Verb	Adverb
riser pipe	Yes	No	No	No
riser main	Yes	No	No	No

As nouns, riser pipe and riser main are synonyms defined as:

Other synonyms of riser pipe include riser, riser pipeline.

riser pipe (noun)	riser main (noun)
a vertical pipe in a building	a vertical pipe in a building