Failure due to abrasion is most likely to occur in dynamic seals. The surface of the O-ring in dynamic contact with the mating part gradually becomes worn and flattened. Wear lines parallel to the direction of movement are often visible within this flattened area. While flattening on one side of an O-ring’s cross-section is indicative of abrasion failure, flattening on both sides is an indication of compression set. For more information on compression set see Diagnosing O-Ring Failure: Compression Set.

Directly or indirectly, improperly finished metal surfaces usually contribute to abrasion failure. Surfaces that are too rough (generally greater than 32 microinches RMS for static seals or 16 microinches RMS for dynamic seals) directly abrade the seal material. Surfaces that are too smooth (less than 5 microinches RMS) lack the necessary pockets or cavities that act as reservoirs for lubrication. Either way, the O-ring suffers. Figure 128 is an illustration of O-ring failure due to abrasion.

Even if the surface finish is correct, failure to keep the seal properly lubricated will lead to abrasion problems. Lubrication concerns can often be alleviated through the use of either internally lubricated or surface-treated O-rings.

Also keep in mind that abrasive contaminants in the system fluid(s) can damage seals and should be excluded and/or filtered out. Polyurethane, carboxylated nitrile, and hydrogenated nitrile all offer increased abrasion resistance.