O-ring resistance: 10 questions and answers
Resistance determines the service life of every seal. We answer the ten most important questions on media, temperature, pressure, ageing and material selection, precisely and with a practical focus.
- Resistance results from the interplay of medium, temperature, pressure and environmental influences such as UV light and ozone.
- The chemical compatibility between material and medium is the most important prerequisite against swelling and material failure.
- Every material has a fixed operating temperature range. Outside it, the material ages or becomes brittle more quickly.
- FFKM offers the broadest chemical and temperature resistance, while FKM is suitable for heat and many chemicals.
- Correct storage, protected from UV light, ozone and deformation, preserves the material properties throughout the entire shelf life.
What is O-ring resistance about?
The resistance of an O-ring determines whether a seal holds reliably for years or fails prematurely. Resistance is not a single value here, but the interplay of several influences: the medium the O-ring is in contact with, the operating temperature, the applied pressure and external factors such as UV light and ozone.
What always matters is the combination of material and operating conditions. An O-ring that seals reliably for years in one application can become brittle or swell within a short time in another. This is why every material selection begins with a precise assessment of the conditions. A first point of reference is provided by our O-ring resistance tool for various media.
What matters
Frequently asked questions
How do you test O-ring resistance?
To test the resistance of O-rings, standardised tests are carried out under simulated operating conditions. These include compatibility tests with various media (oils, gases, chemicals), thermal cycling tests, pressure load tests as well as ageing and wear tests.
These tests measure the physical changes of the O-ring, such as volume change, hardness change and cracking, in order to determine suitability for specific applications.
| Test type | Description | Objective |
|---|---|---|
| Compatibility tests | Exposure to specific media at various temperatures. | Determination of chemical resistance. |
| Thermal cycling tests | Exposure to extreme temperatures and rapid temperature changes. | Assessment of thermal resistance. |
| Pressure load tests | Application of pressure and inspection for leaks or structural changes. | Testing of pressure resistance and tightness. |
| Ageing and wear tests | Long-term tests under accelerated ageing conditions such as UV light, ozone or high temperature. | Assessment of long-term durability and wear resistance. |
How does temperature affect O-ring service life?
The service life of an O-ring is significantly affected by temperature. High temperatures can make the material age faster, soften it or even decompose it, while very low temperatures can make it brittle and prone to cracking.
The optimum operating temperature depends on the material of the O-ring. Exceeding the limits leads to accelerated degradation and a shortened service life. It is important to select the right material for the specific application temperature.
| Temperature range | Effects |
|---|---|
| High | Accelerated ageing, softening, chemical degradation. |
| Low | Hardening, brittleness, cracking. |
How do you recognise O-ring wear?
O-ring wear can be recognised by physical changes such as cracking, hardening, softening, deformation or surface erosion. Further indicators are a drop in performance, for example leaks or pressure loss in a sealed system.
Regular inspections and monitoring of the operating conditions are essential in order to identify signs of wear early and prevent failures.
| Wear phenomenon | Causes | Consequences | Test methods |
|---|---|---|---|
| Cracking | Ageing, ozone, UV light | Leaks, loss of function | Visual inspection, microscope |
| Hardening | Exposure to cold, ageing | Brittleness, embrittlement | Hardness test |
| Softening | Chemical exposure, heat | Material loss, leaks | Hardness test, weight measurement |
| Deformation | Excessive load, heat | Loss of fit, seal failure | Dimensional check, visual inspection |
| Surface erosion | Abrasive media, turbulence | Leaks, loss of efficiency | Visual inspection |
How do chemicals affect O-rings?
Chemicals can affect O-rings in various ways, depending on the material of the O-ring and the type of chemical. Some chemicals cause swelling, softening or dissolution of the material, while others can lead to hardening or cracking.
The chemical compatibility must be checked carefully before selecting an O-ring material for a specific application, in order to avoid material failure and system failures. You can find background on this in our article on the swelling of O-rings.
| Material | Chemical resistance | Susceptible to | Application area |
|---|---|---|---|
| Nitrile rubber (NBR) | Oils, greases | Ketones, ozone, strong acids | General industry, automotive |
| Fluoroelastomer (FKM) | High-temperature oils, chemicals | Ketones, low-molecular-weight esters | Chemical industry, aerospace |
| Ethylene propylene diene monomer (EPDM) | Water, steam, alcohols | Mineral oils, hydrocarbons | Sanitary, automotive, HVAC |
| Silicone | Heat, ozone, UV light | Aliphatic hydrocarbons, acids | Medical, food, aerospace |
| Perfluoroelastomer (FFKM) | Almost all chemicals | Fluorinated solvents | Chemical processing, semiconductors |
How do you select resistant O-ring materials?
Selecting resistant O-ring materials requires a careful assessment of the operating conditions such as temperature, pressure and chemical exposure. Materials such as nitrile rubber (NBR) are suitable for oil-based applications, while Fluoroelastomer (FKM) offers high resistance to heat and chemicals.
For extreme temperatures and chemical exposure, perfluoroelastomers (FFKM) are ideal. Compatibility with the media, the operating temperature and the mechanical requirements are decisive for material selection.
| Material | Resistance | Application | Temperature | Special feature |
|---|---|---|---|---|
| NBR | Oil, water | Automotive, hydraulics | −30/+120 °C | Good abrasion resistance |
| FKM | Chemicals, heat | Chemical, aerospace | −25/+200 °C | Excellent chemical resistance |
| EPDM | Steam, UV light | HVAC, sanitary | −45/+150 °C | Good weather resistance |
| Silicone | Extreme temperatures, UV light | Medical, food | −60/+200 °C | Flexible at low temperatures |
| FFKM | Almost all chemicals | Semiconductors, chemical | −40/+340 °C | Highest chemical and temperature resistance |
How do you store O-rings correctly?
Correct storage of O-rings is crucial for maintaining their service life and performance. O-rings should be stored in a cool, dry room away from direct sunlight, ozone sources and extreme temperatures. The packaging should not be opened until use in order to avoid contamination.
It is important not to stretch, compress or store O-rings under load, as this can lead to deformation. Observing the storage conditions and storage periods helps to preserve the integrity of the material.
| Storage condition | Guideline | Purpose |
|---|---|---|
| Temperature | Cool, stable range (ideally 15-25 °C) | Avoidance of material degradation |
| Light avoidance | Dark storage, away from direct UV light | Protection against ageing caused by UV radiation |
| Ozone protection | Store away from ozone sources | Avoidance of cracking caused by ozone |
| Humidity control | Dry environment, control relative humidity | Prevention of moisture damage |
| Packaging | Keep the original packaging closed until use | Protection against contamination and deformation |
| Deformation protection | No stretching or compression | Preservation of the original shape and function |
How does pressure affect O-ring resistance?
Pressure significantly affects O-ring resistance by increasing the physical load on the material. Under high pressure, extrusion and deformation of the O-ring can occur, which impairs the sealing capability.
Selecting an O-ring with sufficient hardness and using back-up rings can help to improve resistance against high pressures. Material selection and design must take the specific pressure conditions of the application into account in order to ensure optimum performance and longevity.
| Factor | Effect on O-ring | Measure for improvement |
|---|---|---|
| High pressure | Can lead to extrusion and deformation | Use of back-up rings |
| Material hardness | Affects the resistance capacity | Selection of a material with suitable hardness |
| Design | Determines susceptibility to pressure load | Optimisation of the groove design |
| Operating temperature | Affects material behaviour under pressure | Selection of temperature-resistant materials |
| Pressure fluctuations | Lead to cyclic loading | Design adjustments for dynamic applications |
How do you test O-rings for oil resistance?
Testing O-rings for oil resistance is done by means of long-term exposure tests, in which the O-rings are exposed to various oil types at different temperatures. After exposure, the O-rings are examined for changes such as volume increase, hardness change and cracking.
The selection of the O-ring material is based on the test results in order to ensure compatibility with specific oil types. Materials such as nitrile rubber (NBR) and fluoroelastomer (FKM) are known for their good oil resistance.
| Test method | Parameter | Change |
|---|---|---|
| Long-term exposure | Oil type, temperature | Volume increase, hardness change, cracking |
| Volume measurement | After exposure | Volume increase |
| Hardness test | Before and after exposure | Hardness change |
| Crack inspection | After exposure | Cracking |
| Material selection | Based on results | Compatibility with oil types |
How do you prevent O-ring ageing?
The ageing of O-rings can be minimised by selecting the right material, appropriate storage and regular maintenance. Materials such as EPDM and silicone offer excellent ageing resistance. O-rings should be stored cool, dry and away from direct sunlight as well as ozone sources.
Regularly checking and replacing O-rings in critical applications also helps to minimise the risks caused by ageing.
| Preventive measure | Description | Purpose |
|---|---|---|
| Material selection | Use of ageing-resistant materials | Extension of service life |
| Appropriate storage | Cool, dry, protected from UV and ozone | Avoidance of premature degradation |
| Regular maintenance | Inspection and replacement at signs of ageing | Prevention of failures |
| Avoidance of harmful influences | Keeping away chemicals that can attack the material | Protection against chemical degradation |
| Design optimisation | Adapting the design to minimise stresses | Reduction of mechanical ageing |
How does UV light affect O-ring materials?
UV light can significantly damage O-ring materials by causing cracking, colour change and loss of elasticity. Materials such as EPDM and silicone show better UV resistance compared with other materials such as NBR.
Protecting O-rings from direct UV exposure by means of suitable covers or the use of UV-stabilised materials is essential for applications that cannot avoid UV exposure.
| Material | UV resistance |
|---|---|
| NBR (nitrile rubber) | Low |
| FKM (fluoroelastomer) | Moderate |
| FFKM (perfluoroelastomer) | High |
| Silicone | High |
| EPDM (ethylene propylene diene monomer) | Very high |
