Several o‑ring failure modes look the same, and identifying the right root cause is critical to solving the problem. Here are a few lessons learned from some real world applications.
The most common failure mode we see is the flattened o‑ring. When a customer sent me a picture of a flattened o‑ring, they were looking for a more compression set resistant material. However, when we took the o‑ring out of the groove, the bottom side was still perfectly round. This was actually a wear problem caused by a rough surface finish. This is the key to telling them apart, but you have to take the o‑ring out of the groove to see it.
Other common failure modes
- Compression set causes the o‑ring to flatten on both sides.
- Wear causes the o‑ring to flatten on one side only.
Another common failure mode that a customer had was a chewed up o‑ring, but they weren't running at a high enough pressure to really cause extrusion.
In this case, the o‑ring was extruding in both directions which told us that they had a gland overfill problem. They simply had too much o‑ring in the groove. Keep in mind that thermal expansion can cause this, especially when dealing with perfluoronated elastomers.You can also see gland overfill caused by severe chemical swell, but this will also cause the o‑ring to get soft and gummy.