I know the question has been answered already but for information table 121.5 of ASME31.1-2001 gives the following suggested span for pipes in water service for pipes of standard thickness or heavier with operating temperatures up to 400C
NPS inches span in metres
1 2.1
2 3.0
3 3.7
4 4.3
6 5.2
8 5.8
12 7.0
16 8.2
Regards
athomas236