A double-containment piping assembly has two anchor supports, and at least one elbow fitting with an outer elbow section and an inner elbow section received within the inner elbow section. A first leg having a first inner pipe received within a first outer pipe is coupled between an anchor support and the elbow fitting. A second leg having a second inner pipe received within a second outer pipe is coupled between the other anchor support and the other side of the elbow fitting. First flexibility supports are mounted on either side of the elbow fitting, and permit axial and lateral movement of the inner pipe relative to the outer pipe in the areas of the elbow. First axial-guiding supports, which permit axial movement of the inner pipe relative to the outer pipe, but prevent lateral movement of the inner pipe, are each mounted a minimum distance from the elbow fitting between the inner and outer pipes. Any differential expansion of the inner and outer pipes relative to each other accumulates at the elbow fitting, and is absorbed by movement of the inner elbow section relative to the outer elbow section.