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  F.1 General. This appendix addresses and regulates the application of plastic piping for outdoor underground service. The plastic piping may be utilized for outdoor direct burial application.
  F.2 Plastic piping design requirements. Plastic piping, either insert or direct burial, may be installed subject to the following restrictions:
  1. Wherever plastic insert piping is used, the existing piping shall act as a mechanical protection between the plastic piping and the surrounding environment. The gas pipe shall be prepared to the extent necessary to remove any sharp edges, projections, or abrasive material which could damage the plastic during and after insertion. Plastic piping shall be inserted into the casing pipe in such a manner as to protect the plastic during the installation. The leading end of the plastic shall be closed before insertion. Care shall be taken to prevent piping from bearing on the end of the casing.
  2. Persons engaged in the installation of the plastic piping shall be formally trained, qualified, and certified by the serving utility company.
  3. Plastic piping shall not extend more than 3 inches (76 mm) beyond the inner face of the building wall, and shall not be exposed inside the building. Plastic piping may extend into the building a maximum of 1 foot (305 mm) horizontally and 4 feet (1219 mm) vertically immediately adjacent to the inner face of the building wall when encased in a metallic sleeve and constructed and vented so that uncontrolled gas cannot escape from the metallic sleeve inside the building.
  4. Joints shall only be either mechanical or heat fusion joints. Each plastic pipe fusion joint must be made in accordance with written procedures that have been proven by destructive burst test to produce joints at least as strong as the pipe being joined.
  4.1. When plastic pipe or fittings of different material specifications are joined together by heat fusion, a thorough investigation shall be made to determine that the materials are compatible for joining purposes. The joining method used must be compatible with the materials being joined. The recommendations of the manufacturer shall be considered when determining the method to be used.
  4.2. When compression type mechanical joints are used, the gasket material in the coupling must be compatible with the plastic. An internal tubular rigid stiffener shall be used in conjunction with the coupling. The tubular stiffener shall reinforce the end of the pipe and shall extend at least to the outside end of the compression fitting when installed. The stiffener shall be free of rough or sharp edges and shall not be a force fit in the plastic. A split tubular stiffener shall not be used.
  5. Changes in direction with plastic piping may be made with bends, elbows and tees. Bends shall be free of buckles, cracks, or other evidence of damage. No miter joints are permitted. The pipe may be bent or deflected provided the radius shall not be less than the minimum recommended by the manufacturer.
  6. The minimum allowable wall thickness for plastic pipe shall be 0.09 inches (2 mm).
  7. Plastic pipe shall be laid, and continuously supported, on undisturbed or well-compacted soil to minimize shear stresses. Backfill material for at least 4 inches (102 mm) over the plastic pipe shall be free from large rocks or sharp objects. The trench shall be backfilled to a height of 12 inches (305 mm) above the pipe in 6-inch (152 mm) lifts which shall be hand compacted. The remaining trench shall be backfilled in 12-inch (305 mm) lifts.
  8. An electrically continuous corrosion-resistant tracer wire (minimum AWG 14) or tape shall be buried with the plastic pipe to facilitate locating the buried gas pipe. The tracer wire or tape shall be yellow in color. One end of the tracer wire shall be brought aboveground at a building wall or riser for easy identification.
  9. Slack for thermal expansion and contraction or for external loading on direct-buried plastic services shall be provided by snaking the pipe from one side of the trench to the other. Where plastic piping is inserted for a distance of 50 feet (15 240 mm) or more allowances shall be made at the end connections to prevent pull out caused by thermal or by external loading.
  10. External sleeves shall be used on plastic service lines at main connections to minimize shear stresses.
  11. Plastic pipe shall not be installed in areas where it may be exposed to temperatures below 20°F (—7°C) or above 140°F (60°C). Plastic pipe shall not be installed within 35 feet (10 688 mm) of an underground steam facility, nor in any vault in which a steam facility is located.
  12. The specific plastic pipe or fitting to be used shall be thoroughly investigated by the user and material serviceability determined for the conditions anticipated. The selected material shall be adequately resistant to the liquids and the chemical atmosphere which may be encountered. Care shall be exercised at all times to protect plastic material from fire, excessive heat, or harmful chemicals.
  13. The design pressure is not to exceed 100 psig (690 kPa gauge) for plastic gas service piping.
  14. The design pressure for plastic gas service piping or the nominal wall thicknesses for a given design pressure shall be determined by one of the following equations:
(Equation F-1)
(Equation F-2)



Specified outside diameter, inches



Design pressure, psi



Long term hydrostatic strength, psi (Determined in accordance with ASTM D2513)



Specified wall thickness, inches



Plastic design factor = .32



Standard dimension ratio

F.3 Inspection and handling provisions. Plastic piping components are susceptible to damage by mishandling. Gouges, cuts, kinks, or other forms of damage may cause failure. Injurious gouges or grooves shall be removed by cutting out the damaged portion as a cylinder and replacing it with a good piece. Care shall be exercised during handling and installation to prevent such damage. The serving utility shall inspect plastic piping and its components to ensure the absence of imperfections in materials, to ensure sound joints are made, and to ensure conformance with applicable state regulations.

  F.4 Plastic pipe sizing. Tables F.4.1, F.4.2 and F.4.3 shall be used to size polyethylene plastic pipes for various inlet pressures and design pressure drops for plastic piping systems.

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