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The time when the tightness of flange joints was assessed solely by whether they "visibly leak" is a thing of the past in modern industry. Current legislation aimed at air protection and reducing emissions (such as the German TA-Luft directive) requires precise measurement of media leakage.
This is exactly the purpose of leakage classes, which represent a standardized way of evaluating the tightness of flange joints.
Leakage classes are defined as the amount of gas that escapes through one meter of the sealing perimeter per second.
They allow for objective comparison of individual joints, materials, and installation procedures, and set clear technical requirements for tightness.
In practice, we most often encounter the following classes:
From an expert's perspective, it is crucial to understand one thing:
Leakage class is not a fixed property of the sealing.
It is always the result of a combination of:
Even the best sealing in the world will not achieve the required class if it is not properly loaded.
To achieve, for example, class L0.01, the sealing must be compressed with a minimum force defined by the standard EN 13555. If the designer prescribes too low a tightening torque, the required tightness will not be achieved.
Therefore, today, calculating tightening torques according to EN 1591-1 is a necessity for every critical joint.
The following table shows indicative sizes of leaks for different leakage classes at various flange diameters.
| Leakage class | L10⁰ | L10⁻¹ | L10⁻² | L10⁻³ | L10⁻⁴ | L10⁻⁵ | L10⁻⁶ |
|---|---|---|---|---|---|---|---|
| 1 hour (DN 300) | 3.60 | 0.36 | 0.04 | 0.00 | 0.00 | 0.00 | 0.00 |
| 1 day (DN 300) | 86.40 | 8.64 | 0.86 | 0.09 | 0.01 | 0.00 | 0.00 |
| 1 month (DN 300) | 2592 | 259.20 | 25.9 | 2.59 | 0.26 | 0.03 | 0.00 |
| 1 year (DN 300) | 31104 | 3110.40 | 311.04 | 31.10 | 3.11 | 0.31 | 0.03 |
| 1 hour (DN 1200) | 14.40 | 1.44 | 0.14 | 0.014 | 0.00 | 0.00 | 0.00 |
| 1 day (DN 1200) | 345.60 | 34.56 | 3.46 | 0.35 | 0.03 | 0.00 | 0.00 |
| 1 month (DN 1200) | 10368 | 1036.8 | 103.68 | 10.37 | 1.04 | 0.10 | 0.01 |
| 1 year (DN 1200) | 124416 | 12441.6 | 1244.16 | 124.42 | 12.44 | 1.24 | 0.12 |
The table shows that the difference between individual classes can mean orders of magnitude higher or lower leaks in the long term.
The following example illustrates how tightness can have a direct impact on operating costs.
| Parameter | Value |
|---|---|
| Cost of leakage per year from 1 flange | 128 € |
| Cost of leakage at L0.01 | 1.31 € |
| Annual savings on 100 flanges | 12,668 € |
When calculating with the leakage class L0.01, the company:
This is only the savings on media, without accounting for other operating costs.
Long-term practice shows that the best results are achieved by operations that:
Such an approach not only allows for reducing leaks but also stabilizes maintenance and operational planning.
Leakage classes represent the modern language of sealing technology. They allow:
The key to achieving the desired class is not only a quality seal but primarily correct calculation and installation procedure.
If you want to:
we are happy to assist you.
Contact our specialists and schedule a non-binding consultation.
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