Abstract: An apparatus for hardening an elongated steel pipe by quenching the pipe with a cooling medium, particularly water, which apparatus comprises an elongated container dimensioned to receive a hot pipe to be hardened, means for supporting the hot pipe in a predetermined position in said container, a cooling medium nozzle, having a tip, for introducing cooling medium into the pipe through said tip, means for moving said nozzle between a retracted position in which the tip thereof is spaced from an end of said pipe to allow removal and insertion of said pipe with respect to said container and an expanded position in which said tip lies within said end of said pipe, inlet means for introducing cooling medium into said container so as to pass into said pipe through said tip of said nozzle located in said end of said pipe and also to pass around the outside surface of said pipe and an isolator means in fluid communication with said nozzle, movable to vary the relative proportion of volumes of cooling liquid entering