The introduction of restrained joint ductile iron is rapidly gaining acceptance as an alternative pipe material for municipal engineering applications using horizontal directional drilling (HDD). The boltless restrained connection offers flexibility, ease of assembly, and positive restraint against endwise axial separation due to pulling during trenchless installations. The main area of concern is the potential corrosive effects on the pipe from the bentonite-based drilling fluid used in the installation. This paper discusses the results of a field testing program to evaluate the performance of restrained joint ductile iron pipe installed by horizontal directional drilling. The research involved assessment of the installation durability and effectiveness of two combinations of externally applied, loose wrapped, polyethylene encasement to provide a protective barrier. The pipe was excavated immediately and at time intervals of four months, nine months, and thirty-four months post-installation to evaluate pipe material integrity over various time horizons. The study concluded that employing 0.02mm (8mil) linear low-density polyethylene encasement provided the best protection to the ductile iron pipe against corrosion from drilling fluid and soils with low resistivities.