Heat recoverable metallic coupling

A generally tubular article comprising a heat recoverable metallic material above its transition temperature, the article being maintained in a radially expanded, heat-unstable state by a constrained member within its bore, the article being capable, without the application of external force, of expanding radially when cooled to the transition temperature so as to free said member from constraint.

A method of forming a heat recoverable metal article comprising forming said article in a desired configuration from a material capable of having the property of heat recoverability imparted thereto, cooling said article to below the transition temperature of said material, expanding said article while below said transition temperature to an enlarged configuration, said expansion being sufficient to introduce stresses into said material due to non-thermally recoverable plastic deformation, and maintaining said article in an enlarged condition while heating said article to above the transition temperature.

A method of forming a butt joint between two pipes, which comprises expanding a tubular metallic member formed of a material capable of having the property of heat recoverability imparted thereto, expansion occuring at or below the transition temperature of said material to an extent which causes both thermally recoverable and non-thermally recoverable plastic deformation, inserting a mandrel within the member, raising the temperature of the member above the said transition temperature whereby the member shrinks about the mandrel, cooling the member to or below the transition temperature of said material whereby the member spontaneously expands, removing the member from the mandrel, positioning said member about the pipes at their junction, raising the temperature of the member above the transition temperature of said material to cause said member to heat recover on said pipes and maintaining said member above said transition temperature.