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Rigid flanged joints

Technical solutions

Rigid flanged joints

Flanged joints are composed of two flanges, an elastomer joint gasket, and bolts, whose number and dimensions depend on the PN and DN.
The seal is obtained by tightening the bolts, thus compressing the gasket.

The main features are:
- precision of assembly,
- the ability to assemble and dismantle in line.

With DN ≤ 600 the flanges can be rotated, facilitating bolts insertion.


The seal is obtained by compression of a flat elastomer gasket between two flanges. The compression is applied by tightening the bolts, the number of which is a function of the flange PN and DN.
The effective seal is a function of:
- the bolting torque,
- the gasket design (plain, or with reinforcement insert).

The dimensions, positions and numbers of bolt holes are laid down in International Standards, to allow interconnection of all types of fittings, pumps, valves or other accessories.
A distinction is made between:
- rotatable flange joints,
- fixed flange joints.

Flange joints: differences

  • Rotatable flange joints

Rotatable flange joints have mobile flanges mounted on the body.
Rotation of the flanges facilitates connection and bolts insertion.

  • Fixed flange joints

Fixed flange joints have flanges which are integral with the body of the castings.
The flanges are either integrally cast, or welded-on.


Because of its stiffness, the metal reinforced gasket helps in assembly and reduces the risk of extrusion in service.


Flanged pipes and fittings are generally used in above-ground assemblies and installations in valve chambers.
The assembly precision of the joint, and the ability for easy dismantling, makes it particularly suitable for surface installations, or accessible manhole chambers:
- pumping stations,
- valve chambers,
- overhead mains,
- inspection ducts,
- reservoirs, tanks.

Resistance to pressure

The pressure resistance of a flanged component is indicated by its PN.
Flanged pipes and fittings must never be used in service at a maximum pressure greater than that corresponding with their PN.

DNPN 10PN 16PN 25PN 40
40 to 50404853404853404853404853
100 to 5001620251620254048530404853
200 to 300101217162025253035404853
350 to 1200101217162025253035---
1400 to 2000101217162025------
EN 545 - Annex A.4 - Table A.2
For DN 80 flanged parts manufactured by Saint-Gobain Pam, use the following equivalents:


ISO 7005: part 2 : Metallic flanges - Cast iron flanges.
EN 1092-2: Flanges and their joints. Circular flanges for pipes, valves, fittings and accessories, PN designated. Part 2 : cast iron flanges.