Ozone Attack

Ozone attack is a form of chemical incompatibility, however its high frequency occurrence has elevated this unique form of degradation to its own category. Ozone damage occurs mostly with O-rings and seals made from nitrile rubber. The polymer chain in nitrile has a bond which is susceptible to Ozone damage, particularly when the seal is in a stretched position. If the seal is stretched and exposed to the air for a long enough period of time, damage begins at a microscopic level. The polymer chain is cut, initially with very tiny cuts, forming very tiny cracks in the O-ring. As more of the polymer chain is attacked, the cracks increase in both size and frequency until they are quite visible with the naked eye. These cracks are always perpendicular to the parting line and vary in depth and length.

Ozone is only an issue when susceptible seals are held in an stretched position and exposed to the ambient air. Damage is accelerated with increased levels of ozone including what is emitted by electric motors, arc welding, and ultraviolet lights.

Greasing the seal with O-lube or Super O-lube will help protect from ozone to some degree. In addition, packaging the installed seal and hardware in an opaque bag will help protect the seal.

For fittings and hardware which require the seal to be installed and left in the open for a period of time, it may be safer to select a material which is naturally ozone resistant, such as HNBR or EPDM.