Welded and seamless steel pipes
This standard covers the standardization of the dimensions of welded and seamless rolled steel pipes for high, low, and various pressure applications. The term "pipe" used is different from the term "tube" and is applicable to commonly used tubular products of pipeline and pipe system sizes. The outer diameter of pipes with "PIPE" specifications less than or equal to NPS12 (DN300) is larger than their corresponding dimensions. On the contrary, the outer diameter values and corresponding dimensions of the tube "TUBE" are the same for all specifications.
The dimensions of all pipes are identified by the nominal pipe diameter.
The production of tubes NPS ⏵ (DN6) through NPS 12 (DN300) (including NPS 12) is based on a standardized outer diameter (OD). This OD was initially selected to facilitate a standard outside diameter pipe having a wall thickness with periodic characteristics, which would have an inside diameter (ID) approximately equal to the nominal pipe diameter. Although there is no such relationship between the current standard thickness and the outer diameter and nominal pipe diameter, these nominal pipe diameters and standard OD continue to be used as "standards". The production of pipes larger than and equal to NPS 14 (DN350) is based on OD corresponding to the nominal pipe diameter.