Last month, we discussed “nominal diameter” as the term (incorrectly used by drillers) relates to augers, sonic pipe, casing, bits and borehole diameters. When we discuss casing or pipe, “nominal diameter” can be even more confusing; however, it is the origin (and correct use) of the term, taken from the “Nominal Pipe Size” or “NPS” standard sizing system.
Within the NPS system, pipe is described by a nominal diameter (NPS designation) and some dimensionless unit that correlates to wall thickness. Most of the confusion that stems from pipe sizing relates to the wall thickness. So let’s start with the simple, slightly less confusing part: