Frenzelit inner eyelet technology – A new performance class

Novel inner eyelet technology greatly increases sealing performance of static gaskets

Conventional inner eyelet technology is used throughout the chemical and process industry even though it rarely improves the performance of modern gasket materials in terms of their sealing properties, i.e. effectiveness in reducing emissions. Frenzelit has developed a novel inner eyelet technology that advances gaskets with a metal eyelet to a new performance class and actively contributes to the reduction of emissions.
Equipping gaskets with inner eyelets has been standard practice for many years. In this technique, a metal eyelet is incorporated in the gasket. These gaskets are made by pressing thin sheet metal onto the inner or outer cross section of the gasket to create an eyelet. Eyelets were initially developed to improve the sealing performance of the gasket and to protect the cross section from the medium. This keeps the gasket material from coming into direct contact with the medium, thereby preventing contamination of the medium to be sealed. It also increases the stability of the gasket and simplifies the handling, especially with larger geometry dimensions.

Disadvantages of conventional inner eyelet technology
Incorporating metal eyelets in gaskets is still very common practice today. However, modern gasket materials are now much more effective than their predecessors, meaning that improved sealing performance is no longer a valid argument in most cases. In fact, conventional inner eyelet technology often actually has a negative impact on the leakage performance of modern gasket materials. This is because conventional metal eyelets are directly pressed onto the flange, which generally has an uneven, grooved surface. The standard eyelet is unable to adapt to unevenness in the flange surface due to the stiffness of the metal. This creates new possible leakage pathways, as it can lead to surface and cross section leakage (see Fig. 1, top).

New performance class for eyelets thanks to Frenzelit inner eyelet technology
Dr. Anna Berger, Research & Development at Frenzelit, explains the motivation for developing a novel inner eyelet technology: “Improved sealing performance of gaskets with conventional inner eyelets is often no longer a valid argument today. Inner eyelet technology is deeply rooted in many industries and is often required by standards and specifications for historical reasons. So our objective was to advance the established technology to greatly improve the performance capabilities of gaskets with inner eyelets.” This innovative step is based on a novel eyelet that is coated with an elastomer layer. The coating’s flexibility allows for perfect adaptability to the flange and eliminates all of the problems associated with metal-to-metal contact. Flange unevenness is smoothed out and leakage pathways are effectively blocked (see Fig. 1, bottom). The new inner eyelet technology uses a fluorinated elastomer as the coating material which, in addition to its adaptability, has an enhanced chemical resistance. This new technology can be combined with various Frenzelit gasket materials to achieve a significant reduction of leakage rates (see Fig. 2).

An industry breakthrough
There have not been any major developments in inner eyelet technology in recent years. One approach was to increase eyelet adaptability by reducing sheet metal thickness from 0.2 mm to 0.15 mm – and even to 0.1 mm in some cases. But this has led to only very minor, nearly undetectable improvements in leakage rates. In contrast, Frenzelit’s new inner eyelet technology represents a quantum leap in sealing performance. “Our aim for all of our gasket products is to reduce emissions and ultimately improve tightness and longevity of sealing systems. Conventional inner eyelet technology often created more problems than it solved. This inspired us to start looking for ways to improve the existing technology,” explains Dr. Anna Berger.
We have completed the development process and successfully demonstrated the efficacy in long-term tests. Excellent results have been achieved in all laboratory tests, as the leakage curves in Figure 2 illustrate. In order to determine whether the improved leakage properties can also be applied to actual applications in real flanges we have performed leakage tests in modified flanges with defined imperfections. Here as well, the tests demonstrated a significant leakage rate improvement in gaskets equipped with the new Frenzelit inner eyelet technology compared to gaskets with standard eyelets (see Fig. 3). Another impressive feature of the new inner eyelet technology is its increased media resistance compared to conventional metal eyelets. In contrast to stainless steel, which is used in conventional eyelets, Frenzelit’s new technology uses a fluorine-elastomer-coated inner eyelet material that is permanently resistant to oxidizing substances and strong acids such as nitric acid. This opens up completely new technical solutions and areas of application for gaskets with a metal eyelet.
Frenzelit’s new inner eyelet technology will be available June 2021 for novapress® 880 fiber gaskets, novaphit® MST and novaphit® SSTC graphite gaskets (with and without TA Luft treatment and XP technology) and MF-XP corrugated gaskets (semi-metal gasket with a graphite layer).

Future applications with hydrogen
The new inner eyelet technology is of interest for more than just applications in the chemical and process industry; it is also viable for applications with hydrogen, which is currently gaining relevance in many areas (hydrogen production, hydrogen in natural gas grids). Interested parties are asking specifically about the suitability of gasket materials for hydrogen applications. “The molecule’s small size makes sealing hydrogen one of the most challenging tasks,” says Dr. Anna Berger. “We are able to achieve significantly improved tightness classes with the new inner eyelet technology while also ensuring excellent resistance to hydrogen. This means gaskets equipped with the technology will be very interesting for all kinds of future applications with hydrogen.”

For more information contact: I Phone: +49 9273 72-0

Figure 1 – Possible leakage pathways in standard metal eyelets (top) and mode of operation of the new Frenzelit inner eyelet technology by blocking the leakage paths (bottom). Image: ©Frenzelit GmbH
Figure 2 – novapress® 880 featuring Frenzelit’s new inner eyelet technology (blue) vs. conventional competitor products with standard metal eyelets. Image: ©Frenzelit GmbH
Figure 3 – Leakage tests in modified flange with groove (60 μm) to simulate real-world applications (30 MPa, 40 bar N2). Image: ©Frenzelit GmbH
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