Double-containment thermoplastic pipe assembly

A restraint coupling for a double-containment pipe assembly, said pipe assembly comprising a pair of spaced apart axially aligned inner carrier pipes of a first diameter and a pair of spaced apart axially aligned outer containment pipes of a second diameter, said second diameter being greater than said first diameter such that a generally annular space exists between the inner and outer pipes, said restraint coupling being formed from a thermoplastic material of unitary construction and comprising a continuous generally cylindrical containment portion defining a diameter substantially equal to the second diameter and having opposed axial ends for end-to-end axial alignment with the containment pipes, a generally cylindrical carrier portion defining a diameter substantially equal to the first diameter disposed within and generally parallel to said containment portion, said carrier portion having opposed axial ends for end-to-end axial alignment with the carrier pipes, and a connecting portion rigidly extending between and connecting said containment and carrier portions, said containment and carrier portions having longitudinal lengths greater than the length of said connecting portion, said carrier portion extending in opposed axial directions from the connecting portion distances that are at least equal to distances by which the containment portion extends axially from the connecting portion, whereby the carrier portion and the containment portion of the restraint coupling can be fused in end-to-end relationship with carrier and containment pipes of the double-containment pipe assembly.