What type of pipes would use the Standard Dimension Ratio?

The Standard Dimension Ratio (SDR) is typically applied to pipes that are used in specific applications, particularly in the context of irrigation systems. It is a measure that indicates the relationship between the pipe’s diameter and its wall thickness, which helps in determining the pipe's ability to withstand internal pressure.

In irrigation, where systems often deal with varying pressures due to water flow, the SDR provides a standardized way to ensure the pipes are suitable for the operational requirements. This is crucial for maintaining the efficiency and longevity of irrigation installations.

While SDR can indeed be relevant to other types of pipes, such as those designated for high-pressure applications or general plumbing, the question specifically highlights pipes in irrigation systems as the most relevant context for its use. Thus, the focus on irrigation makes it clear why this answer is the most appropriate.