The Ontario Building Code | Steel Pipe
220.127.116.11. Steel pipe
(1) Except as provided in Sentences (2) and (3), welded and seamless steel pipe shall not be used in a plumbing system.
(2) Galvanized steel pipe may be used in a drainage system or a venting ="http://thehandyforce.com/interior/bathroom-renovations/" title ="Toronto Bathroom renovation inspiration">venting system above ground inside a building.
(a) in buildingsof industrial occupancy, or
(b) for the repair of existing galvanized steel piping systems.
(4) Galvanized steel pipe and fittings shall conform to ASTM A53/A53M, "Pipe, Steel, Black and Hot Dipped, Zinc-Coated Welded and Seamless".
(5) Where galvanized steel pipe is used in a drainage system, it shall be used with drainage fittings.
(6) All steel pipe of 4 in. size and smaller shall be schedule 40 or heavier and fittings of less than 2 in. size shall be galvanized screw fittings.