A failed O-ring is a free failure-analysis report — if you read it before discarding it. Each common failure mechanism leaves a characteristic signature on the ring's surface and shape. Match the signature to the table below, and the root cause (and therefore the remedy) is usually clear. This article covers the eight patterns we see most often on returned seals.
| Pattern | What it looks like | Root cause | Fix |
|---|---|---|---|
| 1. Extrusion / nibbling | Ragged, chewed edge or missing chunks on the low-pressure side; thin ‘whiskers’ of rubber | Pressure forces soft elastomer into the clearance gap; pressure cycles shear the protrusion off | Reduce clearance, raise hardness (e.g. 90A), add a back-up ring, or lower peak pressure |
| 2. Spiral failure | Diagonal 45° helical marks or flat cuts around the ring, like a screw thread | The ring rolled/twisted in its groove during reciprocating motion — typically from poor lubrication or eccentricity | Check lubrication and concentricity; use an X-ring, proper surface finish and correct stretch |
| 3. Compression set | Flattened, squarish cross-section that stays deformed; the ring no longer springs back | Sustained squeeze combined with heat, chemical attack, or a compound past its temperature limit | Lower operating temperature, select low-set compound (FKM/peroxide), reduce squeeze into the recommended window |
| 4. Heat hardening & cracking | Hard, brittle feel; radial surface cracks; sometimes charred appearance | Continuous or spike temperatures above the compound rating oxidize the elastomer | Upgrade material (NBR → FKM/FFKM); account for cleaning/startup temperature spikes |
| 5. Chemical attack / swelling | Ring is bloated, soft, tacky or dissolved-looking; may have changed color; breaks easily | Material–media incompatibility — often an overlooked additive, cleaner or blended fuel | Verify the compound against every contact fluid; switch material (e.g. NBR → FKM/EPDM/FFKM) |
| 6. Abrasion / wear | Localized flat spots, shiny worn bands, longitudinal scuffing or scoring | Too-rough or too-smooth? — typically rough shafts, contamination particles, inadequate lubrication, or ring walking | Improve shaft finish and filtration; check lubrication; correct stretch/interference |
| 7. Installation damage | Clean cuts, nicks, pinch marks or tears, often at one location on a brand-new ring | Sharp gland edges, rolling the ring over threads, no installation lubricant, oversized stretch | Chamfer edges, use installation tools/sleeves, lubricate, cover threads |
| 8. Explosive decompression (RGD) | Internal blisters, splits and pits; surface may look intact while the core is cracked | High-pressure gas permeates the elastomer; rapid depressurization expands it internally | Use RGD-resistant compounds/hardness, slow decompression, or specify engineered gas-service seals |
Our experience matches the industry rule of thumb: the majority of returned ‘bad seals’ trace to installation handling, groove geometry or compound mismatch rather than manufacturing defects. The general mechanisms and their prevention are summarized in our earlier article on common causes of seal failure, and the geometry of extrusion failures is covered in detail in Part 5 of the O-Ring Design Reference.
The ring tells you where the problem is. A chewed edge is a pressure story, a flat ring is a heat story, a bloated ring is a chemistry story — inspect before you reorder.
If a failure pattern is unclear, send us photographs of the ring, the groove and the shaft together with the operating conditions. Our engineers will help identify the mechanism and recommend a compound or design change — request support through the O-ring product page.