O-rings, if not handled, used or installed correctly, can be subject to various failures that can impair their functionality and cause leaks or malfunctions in the hydraulic systems in which they are used.
After a malfunction, by observing the condition of the o-ring and carefully checking the operating conditions (operating temperature, pressure, fluids), it is possible to identify the type of failure and thus avoid it.
Let us now look at the most common causes of failure, how to recognise and avoid them.
Abrasion
What you can see. The o-ring has a slightly cut outer surface. Slight scratches with deep cuts or cracks may be present in some parts of the o-ring.
What causes the abrasion. Typical in dynamic environments, the constant friction between the housing and the outer surface of the o-ring causes heating that can lead to rapid deterioration.
How to avoid abrasion. To avoid or otherwise limit o-ring abrasion, always ensure that the sealing system is properly lubricated with fluids free of solid impurities.
Chemical degradation
What you can see. Due to chemical exposure within the application, the o-ring may show more defects such as cracks, staining, discolouration or a difference in hardness.
What causes chemical degradation. Specific chemicals interact differently with different materials. As a result of chemical exposure, the o-ring may appear harder after use, softer or even deformed after a reduction in hardness and strength.
How to prevent chemical degradation. Choose a material with a high degree of compatibility with the chemical fluid. Also keep in mind that chemical degradation occurs faster when temperatures are highand when the o-ring is subjected to excessive pressure.
Chemical swelling
What you can see. The o-ring may appear larger than its original shape, either across the surface or in localised areas.
What causes chemical swelling. Chemical swelling occurs when chemicals penetrate inside the o-ring: the resulting increase in volume can compromise the strength and sealing function of the o-ring.
How to prevent chemical swelling. We recommend using a material with proven resistance to the chemicals inside the application.
Permanent compression
What you can see. Some o-ring surfaces appear flattened, as if they have been levelled to conform to the groove, without returning to their previous shape.
What causes compression. At high temperatures, the o-ring may lose elasticity, shrink and not return to its original shape, causing leaks in the implant. Alternatively, the deformation may be caused by an over-tightened groove. It is also possible that swelling in the volume is due to fluid in the implant and to incomplete vulcanisation of the o-ring in production.
How to prevent compression. Once the correct sizing of the groove has been verified, it is recommended to choose a material with less failure under pressure and/or better sealing at high temperatures. The use of backup rings can also reduce the likelihood of the o-ring being pressed into that permanent oval shape.
Exstrusion
What you can see. On the low-pressure side, the o-ring is eroded or jagged.
What causes extrusion. In high-pressure applications, the o-ring is pushed into a gap between the mating edges.
How to prevent extrusion. We recommend using a harder sealing material and support devices (backup rings) to reduce the likelihood of the o-ring being extruded.
Explosive decompression
What you can see. The o-ring has cracks, blisters and deep cuts that may be visible all over the surface. In the worst case, the o-rings are completely burnt.
What Causes Explosive Decompression. When o-rings are subjected to gas at elevated pressure and temperature for an extended period of time, an abrupt decrease in pressure and subsequent expansion of the ring can cause explosive decompression of the gas, which has previously penetrated below the surface of the o-ring, into the intermolecular spaces.
How to prevent explosive decompression. We recommend, if possible, increasing the decompression time and decreasing the temperature. Also consider using RGD (Rapid Gas Decompression) O-rings with a shore A Viton® 90 and 95 hardness grade and elastomers resistant to explosive decompression (AED).
Spiral Failure
What you can see. The o-ring has deep, diagonal cuts around the outer surface.
What causes spiral failure. Twisting within a dynamic application (or prior to installation) can cause spiral marks on the o-ring. In dynamic application, spiral failure can occur due to several factors including high friction, improper lubrication, or uneven surface finish.
How to Prevent Spiral Failure. We recommend you opt for a harder material. Alternatively, you can use x-rings (also known as quad rings), which are made to double the sealing surface and prevent spiral failure.
Thermal Degradation
What you can see. The o-ring shows radial cracks on the surfaces subjected to high temperatures.
What causes thermal degradation. The temperature within the environment has exceeded the recommended temperature range for that o-ring, permanently reducing its elasticity.
How to prevent thermal degradation. We recommend checking the temperature range of the o-ring compound before use within the application.
Thermal Extrusion
What you can see. The o-ring no longer has a circular profile and 'eroded' edges can be seen on the surface. If in a high-pressure environment, thermal extrusion will be visible on the side of the o-ring that receives lower pressure.
What causes thermal extrusion. Higher temperatures than those for which the o-ring was designed, can cause extrusion of the o-ring and gap filling.
How to prevent thermal extrusion. In addition to material choice, we recommend evaluating the design of the o-ring groove to ensure that excessive compression is not applied to the o-ring, especially when higher temperatures can extrude material to fill the groove.
What you can see. The o-ring shows discolouration spots along the surface of the o-ring. In some cases, the o-ring may show cracks and breaks.
What causes UV degradation. UV light carries high energy in its short wavelengths, which can manipulate the composition of the o-ring. Prolonged exposure can have a damaging impact, which can lead to leakage from the seal.
How to prevent UV degradation. We recommend EPDM o-rings and Viton® o-rings in black for UV resistance.
In conclusion, to prevent the most common failures, always check operating conditions, manufacturer's instructions, installation instructions and regularly monitor the condition of o-rings for replacement when necessary.
