Technical Support

O-Rings
Date: 05.02.18
Technical Support
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.