For butt-weld fittings the only exception to this is; when there is an overall dimension requirement that is greater than the combined total dimensions of the two fittings.    From Wordnik.com.  [CR4 - Recent Forum Threads and Blog Entries] Reference

One such case showed a common control valve station (manifold) which had 11 (eleven) extra and unnecessary "Pup" pieces where butt-weld fittings could have and should have been welded together.    From Wordnik.com.  [CR4 - Recent Forum Threads and Blog Entries] Reference

It is just a butt-weld and if I cannot make a butt-weld between these two round, beveled-end, schedule 40 carbon steel (fitting) objects what if I need to join two other round, beveled-end, schedule 40 carbon steel pipes.    From Wordnik.com.  [CR4 - Recent Forum Threads and Blog Entries] Reference

This specific statement is totally incorrect when applied to 3 "(80mm) and larger butt-weld fittings.    From Wordnik.com.  [CR4 - Recent Forum Threads and Blog Entries] Reference

I suspect that someone, somewhere was listening to instructions about the make-up of piping assemblies for 2 "(50mm) and smaller screwed or socket weld piping and then mistakenly applied the instruction to all piping including large-bore butt-weld piping.    From Wordnik.com.  [CR4 - Recent Forum Threads and Blog Entries] Reference