I have a questions about the black steel pipe for sprinklers, i´m using black steel pipe A795 sch 40 welded, my doubt, why the pipe sch 40 A795 is not UL/FM? and the sch 10 is UL/FM.
Having the UL listing and/or FM approval will depend on the manufacturer. Since the listing/approval cost a lot of money, manufacturers are unwilling to start the process unless they are sure they'll have a return for their investment (ie. increased sales, charge extra, etc.). Since NFPA does not require piping to be listed if they comply with ASTM A53, A135 or A795, you shouldn't have any problem as long as they are sourced from a reputable manufacturer.
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