Fluid Incompatibility is generally recognized by the O-ring exhibiting chemical attack, swelling, or shrinking. Most often with fluid incompatibility, the O-ring will swell in size because the incompatible elastomer is absorbing the fluid. This also results in the O-ring material softening, becoming gummy, which ultimately lead to other failure modes. Other times, the O-ring material will become embrittled, or cracked, sometimes taking a compression set.
Ozone Attack of stretched, nitrile O-rings is an example of fluid incompatibility. Ozone attack is seen by the evenly spaced cracks around the circumference of the O-ring. Ozone degradation is a slow process which is accelerated by O-ring stretch and elevated levels of ozone.
Not as often, but certainly possible, is the O-ring material to shrink. This is a result of components of the compounded O-ring material to extract from the O-ring into the fluid (see animation at below).
Solutions to Ozone degradation are:
1.Select a material with ozone resistance, such as HNBR, FKM, etc.
2.Do not store the O-ring in a stretched condition while exposed to air or ozone.
3.Coat the O-rings with a silicone or petroleum lubricant
Prevention / Correction for Chemical Attack
1.Consult the fluid compatibility guide or an Application Engineer for compatibile materials
2.Verify operating conditions are within the capability of the material
3.Consider the material compatibility of the lubrication.