Method of constructing and installing a direct smelting unit comprising a smelting vessel (11). The vessel is prefabricated off site in three modules (11A, 11B, 11C) which are then transported to the installation site where they are hoisted by a crane and deposited sequentially on top of one another and joined together by welding to form a unitary vessel. The vessel modules are prefabricated so as to be internally lined with water cooling panels connected to water inlet and outlet connectors (62) on the exterior of the circumferential wall sections of those modules. A vessel access tower is formed in modules brought together to envelop the tower and carrying water supply and return piping which is connected to the water inlet and outlet connectors (62) of the cooling panels.