Know How to Identify O-ring Failure in Fluid-Power Systems

Oct 25, 2016 FDA O-Rings

The sealing integrity of a fluid power system is of paramount importance. O-rings are the most common types of sealing used in various fluid power systems. These seals may fail to perform due to various reasons. Analysis of the sealing application will help you understand the nature of failure. This post guides you through various O-ring failure symptoms, the reasons of their formation, and corrective actions.

Guide to O-Ring Failure Troubleshooting

Various studies suggest that most common causes of O-ring failure are:

Incorrect size
Inadequate lubrication for the sealing
Improper installation
Incorrect seal size
Incompatibility between environmental elements and sealant materials
Improper glands

Here are a few symptoms and causes of ring failure:

Compression Set: This is one of the most common causes of O-ring failure. A seal requires a continual seal line between its sealed surfaces. Accuracy of the seal line depends on the gland as well as seal cross-section, which determines the right amount of compression on the O-ring. The most common symptom of O-ring failure by compression is a deformed O-shape, and permanent deformation into a flat-sided oval.

Corrective Action: You can avoid O-ring failure brought by compression set by using an elastomer material, which produces low compression. Also, you need to ensure the right gland design is used for the chosen elastomer.

Chemical Attack: Various chemicals used during the process may attack the elastomeric crosslink, which is responsible for its structural integrity. If you notice splits or blisters on the surface, perhaps your seal is affected by the chemicals used in the process.

Corrective Action: You can avoid this type of failure by selecting an appropriate elastomer compound, which is compatible with chemicals used in the process.

Thermal Degradation: The seals exposed to high temperature for extended periods may harden, and show radial cracks. Most elastomeric materials used for building O-seals are rated with an upper temperature limit. The upper service temperature of the material is often lowered by process chemicals. Thermal failures are usually induced, if seals are used above 25 degrees of the upper service temperature mentioned on it.

Corrective Action: You can avoid this type of failure by selecting an elastomer with a high temperature capability. Also, you can reduce the application temperature, as well as reduce high temperature excursions. You can check with a supplier for a long term data on high temperature exposure.

Abrasion: This may occur due to an improper surface finish coming in contact with the O-ring. The surface finish may be abrasive, or too smooth, which causes inadequate lubrication. Other reasons may include contamination of system fluids, excessive temperatures, and non-lubricating action of the system fluid.

Corrective Action: The problems brought by abrasion can be avoided by using recommended surface finishes for the gland. You can always consider internally lubed elastomers because they help minimize wear and tear.

Nibbling and Extrusion: This type of O-ring failure is common in dynamic applications such as piston seals, hydraulic rods, etc. This type of failure may be introduced in static applications, which are subjected to high pressure. The most common symptoms may include a chipped appearance of the ring, or leakage.

Corrective Action: This type of failure can be avoided by using back-up devices, installing proper sized O-rings, increasing rigidity of metal components, and breaking the sharp edges on the gland with a minimum radius of 0.005 inches.

If you are unable to determine the cause of O-ring failure, you can always approach a sealing expert, or the manufacturer. They will guide you regarding replacements or repairs, as well as help you in keeping conditions in check to avoid O-ring failures.