NPS Pipe Size

NPS Pipe Size

Defining the size of a pipe may at first seem rather simplistic, and initially it was. About 100 years ago, pipes were sized according to their iron pipe size (IPS). If a pipe had an internal diameter of approximately 6 inches, it was classed as an IPS-6 size pipe. The wall thickness of all pipes was standardised (standard (STD)), as was -consequently- their outside diameter.

The IPS system continued to develop as service pressure and temperature ranges increased. To cater for these increased service demands, pipe walls were made progressively thicker and categorised as extra strong (XS)  or double extra strong (XXS). It became obvious to engineers working with the IPS system that continuing to triple extra strong (XXXS) or quadruple extra strong (XXXXS) was illogical, especially since advancements in material science (newly developed alloys etc.) made thinner pipe walls possible. To solve the issues piping engineers were encountering, a nominal pipe size (NPS) system was developed to better suit the constantly changing piping industry