Increasing the tightness of flange connections DN PN

Pressure class PN 40 is the imaginary limit up to which flat cut-out seals can be used relatively safely. From PN 40 onwards, it is recommended to use metallic seals (e.g. spiral wound, ridge, etc.).

The size of the seals is determined by the standard e.g. EN 1514-1. This standard was developed at a time when leakage calculations were unknown. The asbestos gaskets used could be "bled" and then tightened due to absorption. After asbestos was banned, seal materials changed, but their dimensions and installation procedures remained.

In case you want to calculate a flange joint of lower pressure class for tightness according to EN 1591-1, you will find that the calculation may not work out.

What does this mean?

If you use a gasket that is over the entire sealing surface of the flange, the calculation will show that the bolts or flanges are not strength compliant. You are unable to achieve sufficient specific pressure on the seal without tightening the bolt or bending the flange during installation.

Such a joint will only seal at the cost of a tightened bolt or bent flange.

To be sure that the flange joint is properly designed, a leak proof calculation must be performed and the seal size optimized.

It is worth optimising the seal size, for example, for piping routes. Based on the tightness class for which the joint has been calculated, you can declare the maximum amount of emission leakage from the entire route.

The reliability of the flange joint is further increased:

• using the bolted joint lubricant specified in the calculation
• using flat washers
• expert installation
• controlled tightening by trained fitters in accordance with EN 1591-4

We will be happy to help you with tightening torque calculations and optimization of seal dimensions. If you have any questions, please do not hesitate to contact us directly or via our contact form at www.tesneni.cz.

In future editions of our newsletters we will cover the following topics, among others:

• material limits of fiber rubber gaskets
• what to watch out for with graphite gaskets
• Coated gaskets as a relic of the "asbestos age"
• lubrication of bolted joints and its effect on the transmission of tightening forces
• the development of standards for the installation of flanged joints
• training of fitters to EN 1591-4

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