Ozone is NOT a Friend of O-rings!
Have you ever pulled an o-ring to use and discovered that it is full of cracks? Have you ever wrapped something in a rubber band and the rubber band develops cracks and eventually breaks? That is ozone cracking. This is not a quick process, it takes time for the break down.
Ozone cracking occurs mostly with o-rings made from nitrile rubber or buna. Exposure to ozone gradually breaks down the polymer links.
Nitrile is made up of carbon, hydrogen and nitrogen units bonded together, but there are weak links in the bond. Oxygen atoms connect to the carbon atoms at the weak link. The ozone attacks the weak bond, creating the cracks.
O-rings are at risk in their application environment if exposed to ozone, but also if stored for long periods in bad conditions. Here are some recommendations for storing O-rings to avoid exposure to the ozone:
- Keep them away from ultraviolet light, direct sunlight and fluorescent light.
- Do not store o-rings within 6 feet of an electric motor or other potential sources of electrical arcs.
- Do not store o-rings in a stretched state. O-rings typically need to be stretched for ozone cracking to occur.
These are some helpful recommendations for installing o-rings:
- Install the o-rings on mating parts within 24 hours of installing the o-ring on the fitting. If the o-ring must be stored in a stretched state, store them in an airtight bag until ready to use.
- Assemble nitrile o-rings wet with a grease to protect from ozone.
In applications where long-term environmental exposure is the case, there are many alternate ozone-resistant o-ring materials to consider, including HNBR, EPDM or fluorocarbon.