We usually describe the different pipe classes and materials in very basic sizing terms (for example: ½”, 2”, 6”, sched 40 or DR 11). Sometimes, we clarify by saying metric or IPS, but do we really appreciate the nuances of what we are saying? Do we really understand how the thickness, type of material, or even size, impacts the performance of a system?

What’s the big deal? Well, if you choose another material for a particular application, instead of steel, then you need to know more than the nominal pipe size to judge flow rates, velocities, and pressure drops. Just saying 2” PVC doesn’t give you all the information you need. You still need to know if it’s a schedule 40 or schedule 80. Similarly, you need to know if PP-RCT is SDR 9 or SDR 11. In these cases, the wall thickness, adjudicated by either pipe schedule or SDR, will affect the ID and therefore the flow characteristics. For example, PEX tubing, has an ID of 2” but will the material be sufficient for the system requirements?

Read more here.