Extrusion (and/or Nibbling)

Description: The o-ring or seal develops ragged edges (generally on the low-pressure side) which appear tattered.

Contributing Factors: Excessive clearances. Excessive pressure. Low-modulus/hardness elastomer. Excessive gland fill. Irregular clearance gaps. Sharp gland edges. Improper sizing.

Suggested Solutions: Decrease clearances. Higher-modulus/hardness elastomer. Proper gland design. Use of polymer backup rings.

Over-Compression

Description: The o-ring or seal exhibits parallel flat surfaces (corresponding to the contact areas) and may develop circumferential splits within the flattened surfaces.

Contributing Factors: Improper design-failure to account for thermal or chemical volume changes, or excessive compression.

Suggested Solutions: Gland design should take into account material responses to chemical and thermal environments.

Spiral Failure

Description: The o-ring or seal exhibits cuts or marks which spiral around its circumference.

Contributing Factors: Difficult or tight installation (static). Slow reciprocating speed. Low-modulus/hardness elastomer. Irregular O-ring surface finish (including excessive parting line). Excessive gland width. Irregular or rough gland surface finish. Inadequate lubrication.

Suggested Solutions: Correct installation procedures. Higher modulus elastomer. Internally lubed elastomers. Proper gland design. Gland surface finish of 8-16 microinch RMS. And possible use of polymer backup rings.