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Failure Modes

A premature O-ring failure in service is often due to a combination of root causes and not merely a single failure mode.

The following summary of O-ring failure patterns is intended to give the designer an overview of the most common reasons for failures, plus suggested corrective actions.

By utilizing good design practices, seal life will be maximized and reliability increased.

Compression Set

Compression Set is when the O-ring ceases to be “O” shaped and is permanently deformed into a flat sided oval, the flat sides of which were the original sealing faces.
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Extrusion and Nibbling

A typical example of O-ring extrusion is when edges of the ring on the low pressure or downstream side of the gland exhibit a “chewed” or “chipped” appearance.
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Spiral Failure

Spiral failure is characterized by cuts in a spiral pattern along the length of the O-ring. Most often found in a dynamic application.
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Rapid Gas Decompression

The seal exposed to high pressure explosive decompression will often exhibit small pits or blisters on its surface. In severe cases, examination of the internal structure of the O-ring will reveal other splits and fissures.
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Abrasion

Abrasion is caused by the wearing away of an O-ring surface by mechanical action such as rubbing, vibrating or scraping.
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Installation Damage

An O-ring that is sheared, nicked or cut during installation can immediately cause leakage when placed into service. This damage can be caused by sliding the O-ring over sharp corners or threads, insufficient lead-in chamfer on the mating hardware, an O-ring that is improperly sized and even if no O-ring lubricant is applied.
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Fluid Incompatibility

Fluid Incompatibility is generally recognized by the O-ring exhibiting chemical attack, swelling, or shrinking.
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Gland Overfill

With a similar appearance to extrusion, gland overfill failure mode also has the unique, “tails” of O-ring material. The difference is the tails extend out from both corners of the groove, and, if significant, you may see the round O-ring cross section now resembles a square.
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Ozone Attack

Ozone attack is a form of chemical incompatibility, however its high frequency occurrence has elevated this unique form of degradation to its own category.
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