Catalog

Outside Diameter

The outside diameters of pipes are described by the “Nominal Pipe Size”, shown in specifications as NPS and often incorrectly called “inches”. In more recent times with the introduction of the metric system and with the usage of the same pipes in Europe, a metric version has been developed called DN, or “Diameter Nominal”, often incorrectly called “millimetres” and also incorrectly referred to as Nominal Bore or NB. The pipe sizing system did originate with an understanding that then standard pipe sizes when used at the then most typical wall thickness gave an internal diameter approximately equal to the nominal size. With the current multiplicity of wall thicknesses available the Nominal Bore concept has long since ceased to be relevant, and in fact is now misleading. All pipe is specified by outside diameter, never by inside diameter.

Wall Thickness

Wall thickness of carbon steel pipe to AS/NZS 1163 is specified to hard millimetre thicknesses. Wall thicknesses of carbon steel and stainless steel pipe are also commonly described by a “Schedule Number”, however this notation is avoided to permit selection without having to reference a schedule table.