Answer :
Final answer:
Plastic pipe and fittings for gas piping must conform to ASTM D 2513 and shall be installed outside underground only. Option D.
Explanation:
Plastic pipes used for gas piping need to adhere to ASTM D 2513 standards and are required to be installed externally underground.
The American Society for Testing and Materials (ASTM) has created standardized specifications for various materials, including plastic piping. ASTM D 2513 specifically covers Polyethylene (PE) gas piping systems.
This standard ensures that the plastic pipes have the necessary material properties to safely transport natural gas, considering factors such as pressure ratings and temperature variations.
Hence, the right answer is option D.