Piping in hot oil systems that is 25.4 mm (1 in) in diameter or smaller should be classified as which schedule?

In piping systems, especially those dealing with high temperatures such as hot oil systems, the schedule designation refers to the thickness of the pipe wall and its pressure rating capabilities. For pipes that are 25.4 mm (1 inch) in diameter or smaller, Schedule 80 is recommended for applications that require both durability and resistance to higher pressures and temperatures.

This schedule provides a thicker wall compared to Schedule 40, which offers ample strength but may not be sufficient for all hot oil applications, particularly under higher operational pressures. The increased thickness helps prevent failures due to thermal expansion, potential corrosion, and pressure surges which are important factors in hot oil systems.

The other schedules, including Schedule 10 and Schedule 20, provide even thinner walls and are better suited for lower-pressure applications, which might not withstand the operational demands of a hot oil system effectively. Therefore, Schedule 80 is correctly identified as the appropriate choice for smaller diameter piping in such high-temperature environments due to its superior strength capabilities.