What type of pipe must be utilized for carbon steel liquid lines?

The correct choice highlights the appropriate standards for carbon steel liquid lines. Specifically, A106 and A333 are both specifications for seamless and welded carbon steel pipes that can withstand high-pressure applications and are suitable for various services involving liquids.

ASTM A106 is particularly known for its use in high-temperature service, while A333 is typically used for low-temperature applications, ensuring that the piping maintains integrity under different conditions. Thus, using pipes manufactured to these specifications ensures safety and performance standards in high-pressure liquid service, making them ideal for carbon steel applications.

In contrast, the other options consist of pipes that may not be suitable for high-pressure carbon steel liquid lines. API 5L generally covers line pipe for pipelines and might not meet the specific requirements for liquid services in all cases, while API 5CT is related to casing and tubing for oil and gas wells and is not focused on liquid transport at high pressures. Lastly, PVC and CPVC piping are plastic materials that are inappropriate for high-pressure applications and are not made of carbon steel, disqualifying them as a viable option for this specific requirement.