Cross-linked polyethylene piping is commonly called “pex pipe”. It is the material used for water supply in domestic plumbing. The Uponor/Wirsbo sprinkler systems and the Kwench fire sprinkler systems in NFPA 13D fire sprinkler systems use this 1/2″ pex pipe in interconnection with the domestic plumbing.
NFPA 13 requires that fire sprinkler system piping be listed for no less than 175 psi, and be able to withstand a hydrostatic test of 200 psi for 2 hrs, and in some cases slightly more than 200 psi. To meet the listing for 175 psi pipe, the pipe must be able to withstand a burst pressure of 5 times the listing, which is 875 psi. If the fire sprinkler system is interconnected with domestic plumbing, then the fire sprinkler portion of the piping must be listed at no less than 130 psi. The reason for a lower listing in this case is because domestic plumbing will not be able to withstand much more than 130 psi. To meet the listing for 130 psi piping, the pipe must be able to withstand a burst pressure of 5 times the listing, which is 650 psi.
Pex pipe can easily pass the 650 psi burst test at room temperature, but it does not quite meet the 875 burst test. If it did, then it could be used in fire sprinkler systems that are not interconnected with plumbing.