An apparatus for injecting gas into a vessel includes a gas flow duct which receives hot gas through a gas inlet structure at a rear end of the duct. The forward end of the duct has an annular duct with an internal cooling water passage. Cooling water supply and return passages are formed within the wall of the duct such that water flows to and from a tip through the supply and return passages. The tip includes a hollow shell and a partitioning structure that has a ring and a plurality of circumferential flanges that project outwardly from the ring to the shell to form a series of water flow galleries, each extending circumferentially around the tip and interconnected for flow of cooling water sequentially through the galleries from the water supply passages to the water return passage. The circumferential flanges also serve as buttress supports for the shell.