What do DN and PN mean on Flanges?(Video)

How are Flanges Classified?

A flange is an external or internal edge, or a rim (lip), for friction, such as an iron plate flange, such as an I-beam or a T-beam; or for attachment to another part, such as a pipe end flange, a steam ring, etc. When fastened to the pipe, a flange may also be a plate or ring to shape a rim at the end of a pipe. A blind flange is a plate that is used to cover or remove the end of a screw. A flange joint is a pipe attachment, where the connecting bits have flanges which lock the components.

A lot of common flange standards are to be found around the globe. These are designed to have standardized dimensions to allow easy interchangeability and functionality. ASA / ASME (USA), PN / DIN (EU), BS10 (British / Australian), and JIS / KS (Japanese / Korean) are General world standards. In 1996 ANSI stopped publishing B16.5 in the USA and the equivalent for this is ASME B16.5.

There are two pipe types of nomenclature: decimal, and metric. In the imperial system, they use pounds per square inch(psi) to refer to pressure or nominal pipe size(NPS) to refer to the size of the pipes. The pressure would usually be noted in kilopascal (kPa), while pipe diameter is noted in nominal diameter(DN) of the metric system depending on the international unit scale.

What does PN stand for?

PN is an acronym for “Pressure Nominale”. The PN is used as a prefix to the pressure rating of the Flanges. For example, the flange PN16 is designed to operate at up to 16 levels. Normal scores: PN6, PN10, PN16, PN25, PN40, PN64, PN100. Following international flange standards such as ISO 7005-1 or DIN 2501, PN10, PN16, PN25, and PN40 specify both pressure class in pressure bars and metric flange dimensions that use the metric measuring system. Flanges developed to ANSI, AWWA, ASA or old British specifications measured in inches will not necessarily fit with the specification of flanges.

This is probably a good idea to suggest the actual working pressure when defining a PN flange specification as it’s customary to allow a similar PN, say PN16, flange drilling on a fitting or valve to suit neighboring flanges but the pressure level is lower than PN16.

The word nominal diameter refers to a pipe’s internal diameter. All measures of a piping board, together with the approximate pressure level and type rating, e. g. The flange measurements are specified according to the nominal diameter. Steel is not often defined as a commodity yet thought to be.

It should be noted that the true internal diameter in many instances deviates by several millimeters. Only when the nominal diameter DN is specified concerning the equivalent DIN norm can it be accurately concluded that pipes from different manufacturers can be mixed.

The nominal diameter is specified using the DN (Diameter Nominal) abbreviation in compliance with EN ISO 6708 followed by a dimensionless number equivalent to the real internal diameter in millimeters. For reference, a DN 50 pipe indicates a pipe with an external diameter of 60.3 mm and a wall thickness of 3.65 mm according to EN 10255 (resulting indoor diameter of 53 mm).