High pressure CO2 systems require Schedule ___ or ___ pipe, depending on the pipe size.

• A. Schedule 20 or Schedule 40
• B. Schedule 60 or Schedule 120
• C. Schedule 10 or Schedule 20
• D. Schedule 40 or Schedule 80

Answer: (D)

Pipes use schedule numbers to denote wall thickness and the corresponding pressure rating for a given material. In high‑pressure CO2 systems, you must choose a pipe that can safely handle the internal pressure for the specific diameter. Schedule 40 provides the needed strength for many smaller CO2 lines, while Schedule 80 has a thicker wall to meet higher stress requirements on larger-diameter lines. This pairing of 40 or 80 covers the standard ranges you’ll encounter for high‑pressure CO2 piping, which is why it’s the correct choice. The other options either reflect wall thicknesses that are too thin for high pressure or combinations not typically used in these systems.