Why did it fail? · 11 failure modes

O-ring failure diagnosis: match the damage to the cause

Look at the old ring, find what you see below, then check the likely causes before you order a replacement. The same failure comes back if only the ring is changed.

Start the step-by-step diagnostic Measure the old ring →

Screening guidance from common failure patterns, not an engineering approval.

Reference

What you see, the likely cause, what to check

Leakage

What you seeFluid weeps past the seal, often with no visible damage on the ring.

Causes and checks

Likely causes

  • Too little squeeze (groove too deep or ring too small)
  • Scratched or rough sealing surface
  • Ring damaged or twisted during fitting
  • Wrong size after a substitution

Check

  • Measure the ring and the groove depth and compare the squeeze
  • Inspect the sealing faces for scratches and the finish
  • Look for cuts or a flat spot on the ring
Measure the ring Check the groove →
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Extrusion and nibbling

What you seeThe edge on the low-pressure side looks chewed, peeled or has thin flaps.

Causes and checks

Likely causes

  • Gap too wide for the pressure
  • Hardness too low for the pressure
  • Pressure peaks or a gap that opens under load
  • Sharp groove edges

Check

  • Account for the radial gap at peak operating pressure, including elastic deformation, using approved calculations or a safe validated test method
  • Note the peak pressure, not only the working pressure
  • Check the hardness of the old ring
Check the gap in Engineer Pro Pick a harder grade →

Swelling

What you seeThe ring is bigger, softer or sticky and may fall out of the groove.

Causes and checks

Likely causes

  • The rubber family does not resist the medium
  • A cleaning agent or additive the seal was not chosen for
  • Higher temperature than planned speeds up the attack

Check

  • List every fluid the seal touches, cleaners included
  • Compare the ring with a new one: size and hardness
Screen the media Choose another family →

Compression set

What you seeThe ring keeps a flat, square or D-shaped section and no longer springs back.

Causes and checks

Likely causes

  • Temperature above what the compound tolerates
  • Too much squeeze
  • Long service life or a compound with poor set resistance

Check

  • Check the real temperature at the seal
  • Check squeeze against the reference range
  • Note how long the ring was in service
Check squeeze Compare families →

Cracking

What you seeFine cracks on the surface, often at right angles to the stretch.

Causes and checks

Likely causes

  • Ozone, sunlight or weather on a family that does not resist it
  • Heat ageing
  • Too much stretch on the inside diameter

Check

  • Is the seal outdoors or near electrical equipment (ozone)?
  • Check installed stretch
  • Check the temperature
Select for ozone Check stretch →

Hardening

What you seeThe ring is hard, glassy or brittle and may crack when bent.

Causes and checks

Likely causes

  • Service above the temperature limit
  • Heat ageing over time
  • Some media extract the softeners from the rubber

Check

  • Compare the hardness with a new ring
  • Check the peak temperature
  • Check the media
See temperature ranges Screen the media →

Softening

What you seeThe ring is soft, gummy or leaves residue, without much swelling.

Causes and checks

Likely causes

  • Chemical attack
  • Temperature too high for the compound
  • Wrong family for the medium

Check

  • Wipe the ring: residue points to chemical attack
  • List media and cleaners
  • Check the temperature
Screen the media Ask for a review →

Spiral twist

What you seeMarks run around the ring like a barber's pole; the ring may be cut in places.

Causes and checks

Likely causes

  • Rolling in a reciprocating gland
  • Uneven surface finish or poor lubrication
  • Long stroke at low speed
  • Groove too wide

Check

  • Look for a twist line on the ring
  • Check lubrication and the finish
  • Check the gland width
Check the dynamic gland Check the groove →

Wear and abrasion

What you seeA flat, shiny or scored band on the dynamic side of the ring.

Causes and checks

Likely causes

  • Rough counter-surface
  • Too little lubrication
  • Speed too high for an O-ring
  • Dirt or particles in the medium

Check

  • Check the surface finish of the moving part
  • Check lubrication and contamination
  • Check speed and stroke
Select for dynamic service Check the gland →

Installation cuts

What you seeA clean nick, cut or peeled strip, usually found right after assembly.

Causes and checks

Likely causes

  • Sharp edges, threads or ports crossed during fitting
  • No lead-in chamfer
  • Ring twisted or pinched while closing
  • Fitted dry or with dirt on the parts

Check

  • Find where the cut sits and what the ring passed over
  • Check the chamfer and cover the threads
  • Check the ring size against the groove
Follow the installation steps Measure the ring →

Explosive decompression

What you seeBlisters or pits on the surface; cut open, the ring shows splits inside.

Causes and checks

Likely causes

  • High-pressure gas soaked into the rubber
  • Pressure released too fast
  • A compound not made to resist decompression

Check

  • Note the gas, the pressure and how fast it was released
  • Cut a failed ring open and look for internal splits
Ask for a review Compare families →

Damage looks different?

Describe the pattern and the service conditions in the step-by-step diagnostic below. It ranks the likely causes and shows what to check next.

Open the diagnostic

Screening guidance from common failure patterns, not an engineering approval. For critical or repeated failures, send photos of the ring and the operating conditions for a review.

Next step

Fix the cause, then order the replacement

A new ring of the same grade usually fails the same way. Change what caused the damage first.

Shop by materialNBRFKMEPDMSiliconeFFKM
Find the replacement size

OXXRING ENGINEERING TOOLS

Seal Failure Diagnostic

Describe what you see and the service conditions. The tool ranks plausible failure mechanisms and shows what to check next.

Screening only — appearance alone cannot prove a root cause. Final diagnosis requires geometry, material, media, motion, pressure, temperature and service history.

1. What does the O-ring look like?

2. Add service context

No diagnosis yet.Describe the visible pattern first. Results will be ranked hypotheses, not a single claimed root cause.

Next engineering path

Chemical CompatibilityUse when swelling, softening or media attack is suspected. Engineer ProUse for squeeze, clearance, extrusion, pressure and groove review. Size FinderUse when damage may come from incorrect size or old-ring measurement. Application ReviewSend the failure context for engineering review.