Flanges to EN 1092-1: Types, Sealing Faces and Pressure Ratings

Anyone who plans or installs in piping and plant construction cannot avoid EN 1092-1. The standard specifies dimensions, types and the pressure-temperature rating for circular steel flanges, and thereby forms the basis for flange, mating flange and gasket to match one another. To make the right selection, it pays to take a systematic look at types, sealing faces, pressure ratings and materials.

Placing EN 1092-1 as a dimensional standard

EN 1092-1 is the central dimensional standard for circular steel flanges with a PN designation. It defines connecting dimensions such as outside diameter, bolt circle, number and diameter of bolt holes, as well as the design of the sealing face. The PN designation ensures that flanges of the same nominal size and the same pressure rating share a compatible bolt pattern. Distinct from these are flanges to American standards (Class designation), which have different bolt patterns and cannot readily be combined with PN flanges.

Types and designs

Depending on the connection type, loading and material of the piping, different designs come into use. The most common are:

• Weld-neck flange: with a weld neck and weld-on end, well suited to high loading and fluctuating pressures.
• Blind flange: for the tight closure of line ends or branches.
• Lap-joint flange with stub end or weld-on collar: the loose flange ring rotates freely, the collar takes up the sealing force & makes it easier to align the bolt holes.
• Threaded flange: without a weld, for applications where welding is not intended or not possible.
• Slip-on flange (weld-on plate flange): slipped over the pipe end and welded, an economical solution in the lower pressure range.

Sealing faces and gasket seats

The form of the sealing face must suit the gasket used and the medium. EN 1092-1 recognizes several established designs:

• Flat (raised) face (form B1/B2): the standard for flat gaskets, with B2 having a finer finish, for example for soft-material gaskets.
• Tongue and groove: positive location of the gasket, good at higher pressures and with critical media.
• Male and female face: similar logic with a defined recess for the gasket.

It is important that both flanges of a joint match in terms of face form: groove belongs with tongue, male with female. Two flat faces, by contrast, are combined with a matching flat gasket.

Pressure ratings and pressure-temperature rating

The pressure rating is given as a PN nominal pressure; common values are PN6, PN10, PN16, PN25, PN40 and higher. PN is a reference value for identification and component selection, not the permissible operating pressure in a given case. The actually permissible pressure follows from the pressure-temperature rating and depends on the material and the operating temperature: as the temperature rises, the permissible pressure falls significantly. For design, therefore, the combination of PN rating, material and temperature is always decisive, not the PN figure alone.

Choosing the material to match the line

The flange material should suit the piping and the operating conditions. In water engineering and general plant construction, non-alloy structural steels predominate. For higher temperatures, creep-resistant steels are used whose strength is retained in the hot range. Under corrosive loading or high purity requirements, stainless steels are chosen. Make sure that flange and pipe are compatible metallurgically and in welding terms, so that the joint remains permanently tight and load-bearing.

In short: EN 1092-1 organizes circular steel flanges via dimensions, PN ratings and sealing faces. Decisive for a tight, load-bearing joint is that flange type, pressure rating, sealing-face form and material match the piping and the mating flange, and that the permissible pressure is always determined via the pressure-temperature rating of the chosen material.