O-Ring Failures
The failure types identified below are based on historical data and extensive industry research.
CHEMICAL DEGRADATION
Indications: Blisters, cracks, voids or discoloration.
Contributing Factors:
- Incompatibility with the chemical and/or thermal environment
INSTALLATION DAMAGE
Indications: Small cuts, nicks or gashes.
Contributing Factors:
- Sharp edges on glands or components
- Improper sizing of elastomer
- Low-modulus/hardness elastomer
- Elastomer surface contamination
OVERCOMPRESSION
Indications: Parallel flat surfaces corresponding to contact areas; possible circumferential splits.
Contributing Factors:
- Improper design
- Failure to account for thermal or chemical volume changes, or excessive compression
EXTRUSION/NIBBLING
Indications: Ragged edges, generally on the low pressure side.
Contributing Factors:
- Excessive clearances
- Excessive system pressure
- Irregular clearance gaps due to eccentricity
- Sharp gland edges
- Low-modulus/hardness elastomer
- Softening of elastomer due to fluid incompatibility
SPIRAL FAILURE
Indications: Cuts or marks spiraling around 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
EXPLOSIVE DECOMPRESSION
Indications: Surface blisters, pits or pocks. Absorption of gas at high pressure and subsequent rapid decrease in pressure. Elastomer surface blisters and ruptures as pressure is rapidly removed.
Contributing Factors:
- Rapid pressure changes
- Low-modulus/hardness elastomer
ABRASION
Indications: Flat surface parallel to the direction of motion; loose particles and scrapes on surface.
Contributing Factors:
- Rough sealing surfaces
- Excessive temperature
- Process environment containing abrasive particles
- Dynamic motion
- Poor elastomer surface finish
CONTAMINATION
Indications: Foreign material on the surface or within the cross section.
Contributing Factors:
- Process environment deposition
- Reactions or degradation of the elastomer
COMPRESSION SET
Indications: Flat-sided cross section corresponding to mating seal surfaces.
Contributing Factors:
- Excessive compression
- Excessive temperature
- Incompletely cured elastomer
- Elastomer with high compression set
- Excessive volume swell in chemical.
PLASTICIZER EXTRACTION
Indications: Often difficult to visually detect; may exhibit a decrease in cross-sectional size.
Contributing Factors:
- Improper or improperly cured elastomer
- High vacuum levels
- Low hardness/plasticized elastomer.
WEATHERING/OZONE CRACKING
Indications: Small surface cracks perpendicular to the direction of stress.
Contributing Factors:
- Exposure to ozone, UV radiation or other air pollutants
- Excessive seal stretch
THERMAL DEGRADATION
Indications: May exhibit radial cracks on the highest temperature surfaces. Certain elastomers may exhibit signs of softening or a shiny surface.
Contributing Factors:
- Elastomer thermal properties
- Excessive temperature excursions or cycling