Abstract: A tubular housing made up of a pair of sections forms a tubular inner compartment of a cross dimension larger than the outer diameter of a pipe in which water is to be frozen. The housing has opposite flanges arranged to be abutted together and bolt fasteners are provided in the flanges for releasably securing the housing sections together for installing and removing them laterally on a pipe. The end walls of the housing have openings arranged to fit around the pipe on which the housing is mounted and such openings have seals to provide a sealed engagement with the pipe. An inlet for freezing material extends into one side of the housing adjacent one end of the latter and an outlet for gas from the freezing material extends from the housing on the same side as the inlet and adjacent the other end of the housing. The two housing sections are symmetrically constructed whereby the inlet will be in one of the sections and the outlet will be in the other section.