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This practice covers the standard materials and installation procedures for polyethylene encasement to be applied to underground installations of ductile iron pipe for water or other liquids. It may also be used for polyethylene encasement of fittings, valves, and other appurtenances to ductile iron pipe systems. Linear low-density and high-density cross-laminated polyethylene films shall be manufactured of virgin polyethylene material, and shall conform to the required group, density, dielectric strength, and volume resistivity specifications. The polyethylene encasement material shall also be in accordance to the tensile strength, elongation, dielectric strength, impact resistance, and propagation tear resistance requirements. The polyethylene encasement shall be installed in such a way that it shall prevent contact between the pipe and the surrounding backfill and bedding material without intending to be a completely airtight or watertight enclosure. The polyethylene film shall be fitted to the contour of the pipe with sufficient slack to prevent stretching the polyethylene bridging irregular surfaces. For installations below the water table or in areas subject to tidal actions, or both, it is recommended that tube-form polyethylene be used with both ends sealed as thoroughly as possible with adhesive tape or plastic tie straps at the joint overlap.