Baring codes and all that they bring with them, let me add my three cents.
From a complete installation view.
I have always used threaded pipe and fittings for my drains, relief lines et cetera. And always will.
A few years back I was on a project where the foreman wanted to use grooved couplings instead of unions on the floor control drain line to the gang drain connections. I thought it didn't look as professional, nor did it give it the rigidness a union does. While easier to install and repair it just did not look right.
Shortly after on another project the foreman wanted to use CPVC on the packing drip lines and relief line on the fire pump, saying it was easier to unclog the lines if and when that were required. (No glue, just dry fit.)
Yes it was easier to install, but it just did not look right. I guess maybe I am olde school or just too particular (and/or anal retentive).
All the trim and drains on MY projects have been done in steel piping with cast fittings (even the gang drains on CPVC systems), and I have always been quite pleased and proud of the results.
Some consideration should be given to what conditions and stresses these pipes will be under. Be it corrosiveness or incompetent people stepping on them.
Shouldn't the ultimate goal be to give the customer an exceptional quality fire protection system which will operate properly in any situation?
If it cost's my company a few dollars to make me confident that I have done the best job that I could, I am quite satisfied. And may I add, I am proud of all of the job I have installed.
As far as water motor gong piping, I would NEVER, EVER, use CPVC. Even if it were listed and approved by the AHJ, State and Federal Fire Marshal.
But I digress.
As far as code requirements are concerned, cdafd and SD2 have been right on in posts I have seen here and have my utmost respect.
Because ultimately, we are here to save lives and property.
If we all agreed, we would be Communists. - Me