A duct coupling system has a first duct with and end having a threads thereon, a second duct having an end with threads thereon, and a coupler having a first end threadedly engaged with the threads of the first duct and a second end threadedly engaged with the threads of the second duct. The ducts and the coupler are each integrally formed of a polymeric material. A plurality of tendons extend through the interior passageways of the ducts of the coupler.