Common Causes of O-Ring Failure

No one wants seals to fail, however it can happen. In this handy guide, indications of the common causes of O-Ring failure are given with possible contributing factors. But remember, involving Trelleborg Sealing Solutions in the design stage can avoid such issues.

The failure types identified below are based on historical data and extensive industry research.

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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.

ABRASION

• Indications: Flat surface parallel to the direction or 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.

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. Excessive gland fill

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.

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.