Nominal Pipe Size NPS (Nominal Pipe Size) is a dimensionless ordinal number used to denote Pipe Size. It is followed by a number indicating the standard pipe. The IPS system was established to distinguish pipe sizes.

Nominal Pipe Size NPS (Nominal Pipe Size) is the North American standard for high/low pressure and high/low temperature pipes. NPS is based on the earlier IPS (Iron Pipe Size) system. The IPS system was established to distinguish pipe sizes. These dimensions represent the approximate inner diameter of the pipe in inches. An IPS 6" pipe indicates that the inner diameter of the pipe is approximately 6 inches. Users began calling pipes two inches, four inches, and six inches. Early tubes had only one wall thickness per size, which was later referred to as standard wall thickness STD. The outside diameters of the pipes were also standardized.

As industry developed to handle high-pressure fluids, thicker pipes began to be manufactured. Gradually came the thickened tube XS (or XH) and the double-thickened tube XXS (or XXH), but the standard pipe OD did not change.

Schedule of pipe wall thickness

As mentioned above, in the IPS era there were only three wall thicknesses for pipes. In March 1927, the American Standards Committee surveyed the industry and added a smaller grade between the two pipe wall thicknesses, that is, SCH to denote the nominal thickness of the pipe. These thickness classes include: SCH5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS and XXS.

Nominal Pipe Size NPS (Nominal Pipe Size) is a dimensionless ordinal number used to denote Pipe Size. It is followed by a number indicating the standard pipe. For example, the outer diameter of the steel pipe represented by NPS 6 is 168.3mm.

The NPS is not quite consistent with the inside diameter of the pipe. Tubes with NPS12 and below have an outside diameter greater than the number of inches attached to the NPS. Tubes for NPS14 and above have an outer diameter equal to the number of inches attached to the NPS.

For a certain pipe, the outer diameter is fixed, the wall thickness increases with the increase of SCH number, and the inner diameter depends on the SCH ordinal number of the pipe wall thickness.

Abstract:

The size of the steel pipe is determined by the following two dimensionless numbers

NPS size

SCH serial number

The relationship between the above two data determines the inner diameter of the steel pipe.

Stainless steel pipe dimensions are determined by ASME B16.9 for outer diameter and wall thickness series. The wall thickness series of stainless steel tubes is followed by the suffix letter S.

The ISO organization uses DN to represent the nominal pipe size. The relationship between DN and NPS is as follows: