Is schedule 10 piping allowed to be threaded?
The code 'shall' and the annex 'should' seem to be in conflict as you can see below
In the 2016 NFPA 13 it states :
Threaded Pipe and Fittings.
18.104.22.168* Steel pipe with wall thicknesses less than Schedule 30
[in sizes 8 in. (200 mm) and larger] or Schedule 40 [in sizes
less than 8 in. (200 mm)] shall only be permitted to be joined
by threaded fittings where the threaded assembly is investi
gated for suitability in automatic sprinkler installations and
listed for this service.
However in the Annex,
A.22.214.171.124 Some steel piping material having lesser wall thickness
than specified in 126.96.36.199 has been listed for use in sprinkler
systems where joined with threaded connections. The service
life of such products can be significantly less than that of Schedule 40 steel pipe, and it should be determined if this
service life will be sufficient for the application intended.
All such threads should be checked by the installer using
working ring gauges conforming to the “Basic Dimensions of
Ring Gauges for USA (American) Standard Taper Pipe
Threads, NPT,” as per Table 8 of ASME B1.20.1, Pipe Threads,
General Purpose (Inch).