Revolutionary sealing technology of the future

Spring-supported metal seal, combination of elastic and plastic, defined compression in the force shunt

Elastic metal seals are used when the ambient conditions are too extreme for conventional seals. This applies in particular to applications in which hydrogen is used. The currently available elastic metal seals with spring support are increasingly being used in static hydrogen sealing applications, for example in hydrogen tanks for fuel cell drives. High-performance seals are also required for oil or gas production.

Elastic metal gaskets are used where gaskets made of other materials fail. Available in a variety of sizes and shapes, they offer almost infinite durability and long-term sealing performance without porosity. Typical temperature ranges extend from -250 °C to +1,200 °C. These gaskets are used from ultra-high vacuum to high pressure and are helium-tight up to the detection limit for mass spectrometers.

Due to their properties, elastic metal seals are the preferred sealing solution for hydrogen applications, as hydrogen molecules are much smaller than helium molecules. The product of a European gasket manufacturer, made from this material, is increasingly being used in demanding cryogenic and H2 applications. The sealing solution is ideally suited for the future energy medium hydrogen.

Seal characteristics of the force-displacement diagram, defined compression of the seal in the force shunt

The advantages of metal gaskets, including a wide temperature range, suitability for vacuum, UHV and high pressure as well as the absence of porosity and therefore a consistently high sealing effect, are the main focus. Elastic metal gaskets are used in the force shunt and are therefore protected from the operating forces of the flange. The elastic metal gaskets with spring support available today are increasingly being used in static hydrogen sealing applications, such as in hydrogen tanks for fuel cell drives, which must function effectively, very durably and reliably with minimal leakage under extreme operating conditions.

The principle of spring-loaded metal seals

The functional principle of spring-assisted metal seals is based on the plastic deformation of a sheath whose deformability is higher than that of the surface to be sealed. The elastic core of the spring-assisted metal seal consists of a tightly wound coil spring. This spring generates a force and elasticity as resistance to compression. The resulting contact force presses the sealing jacket into the microstructure of the sealing surface. Each individual coil of the coil spring reacts independently and allows the gasket to adapt to unevenness in the sealing surface. This unique combination of elasticity and plasticity ensures efficient sealing, even under critical conditions with repeated decompression of the gasket.

Typical H2 applications of high-performance seals

To cover a significant temperature range while ensuring safe H2 gasket operation in various applications, it is crucial that the gasket elastically springs back with the flange over a wide range of relative movements - while being reliably protected against hydrogen permeability under all operating conditions. This requirement means that the gasket must have effective elastic recovery. The elasticity of the springback increases almost linearly with the larger cross-section of the seal, whereby the contact pressure (Y2 parameter of the seal) plays a decisive role in the design of the seal for hydrogen. In general, it can be stated that as the gasket cross-section increases, the compression force of the gasket or the Y2 parameter in N/mm of the gasket circumference also increases. The flange rigidity and the quality, number and diameter of the flange bolts must also be taken into account appropriately in the design.

At present, high-performance seals have been successfully tested in various plants for gas production and hydrogen applications and are intended for use. In the field of H2 seals and the associated requirements for permissible leakage, there is currently no recognisable regulation according to standards or design standardisation. For this reason, a renowned seal manufacturer designs and offers high-performance seals customised for each application in order to ensure minimum H2 leakage depending on the diameters.

Special FKM compound Vi 900 for the oil and gas industry

Sealing components under harsh conditions

The extraction of oil or gas is extremely complex, time-consuming and cost-intensive in exploration and transport regions, especially in low-temperature areas such as Alaska, Canada and the vicinity of the North Pole. The oil industry plays a crucial role in the Arctic Circle, where the gas and oil reserves to be extracted are of great interest. Although the production of Arctic oil mainly takes place in Alaska, significant oil and gas reserves have also been discovered in the Arctic regions of Canada, Greenland and elsewhere. In these regions, resistance to low temperatures is an essential requirement and represents an absolute limit for elastomer seals in this application area.

Common to all oil wells are the extreme demands placed on the material and components used. Drill heads, for example, have to withstand high drilling mud pressure, vibrations, strong pressure fluctuations and aggressive chemical substances. In deep drilling (downhole drilling), the materials even have to be able to withstand high pressures and extreme temperatures of up to 200 °C at the same time. The use of unsuitable elastomer seals in these areas, such as in the valve controls for motors or trigger mechanisms and measuring devices, can lead to serious damage to an entire machine unit and production must be interrupted.

An O-ring damaged by explosive decompression

One challenge is that the drill head and the entire drive technology can only be monitored to a very limited extent during drilling activity. The conditions several kilometres below the earth's surface are anything but technology-friendly. In addition, it is extremely difficult to replace the seals at drilling depths of over 2,500 metres. If directional drilling technology is used, depths of 5,000 metres can be reached and pipe lengths of up to 11,000 metres are possible. Stopping production under these conditions would have fatal consequences, as the downtime would have a significant impact on productivity and profitability. The running platform and crew costs amount to around 200,000 euros per day. However, costs of up to 500,000 euros per day can also be incurred. The components used in these extreme conditions must therefore be extremely reliable.

Elastomer seals are used in various areas of application, including not only in exploration, but also in the transport, storage and processing of oil and gas as well as in the downstream production of chemical and petrochemical products. These areas encompass a wide range of technical components and assemblies. Elastomer seals play a decisive role in the drive motors of drill heads as well as in gas filters, valves, pipework, fittings, pumps and compressors. They are therefore essential, safety-relevant components in these systems.

Explosive decompression (AED or RGD)

In these areas of application, many operators in the gas or chemical industry and manufacturers of supplier components often face challenges with regard to leakage in elastomer seals, particularly in the event of a significant drop in pressure in the gas medium. In such cases, elastomer seals must fulfil special requirements if they are exposed to gaseous media at pressures of over 30 PN/30 bar and sudden pressure drops (within a few seconds). Only materials that withstand special tests may be used in these applications.

The DIN EN 14141 standard for natural gas pipelines stipulates that non-metallic parts of fittings, including elastomer seals, must be resistant to explosive decompression. This applies to various components such as pumps, compressors, pipelines, connections, fittings and valves.

Due to the high forces in such applications, conventional elastomer sealing materials cannot be sufficiently resistant. Therefore, specially designed elastomers such as AED or RGD (“Anti-Explosive Decompression” or “Rapid Gas Decompression”) sealing materials are used in these applications. These materials can withstand the demanding conditions and the resistance to explosive decompression can be proven by tests according to NORSOK M-710 Rev. 3 (Annex B) and/or ISO 23936-2.