+ O-Ring Failure

Untimely O-ring failure is often the result of the wrong gland design or compound selection. We will examine common causes of premature O-ring failure. It is important to identify what is causing the failure so a change in gland design or compound can correct the issues.

o-rings
Abrasion

+ Abrasion/Frictions

Failure: The O-ring or parts of the O-ring exhibit a flat surface that is parallel to the direction or motion. Loose particles may be found on the surface.

Factors to Consider: Rough mating surfaces.  Extreme temperatures.  Application environment containing abrasive particles.  Dynamic application.  Poor O-ring surface finish.

Possible Solutions: Use recommended gland surface finishes. Use internally lubed O-rings. Eliminate abrasive components from the process.

Chemical-Attack

+ Chemical Degradation

Failure:  The O-ring may exhibit signs of degradation including blisters, cracks, discoloration, or voids.

Factors to Consider:  The material selected is not compatible with the chemical and/or the thermal environment.

Possible Solutions:  Select a compound that is more suitable for the chemical and/or the thermal environment.

Compression-Set

+ Compression Set

Failure:  The O-ring exhibits a flat sided cross section.  The flat sides are consistent with the mating surfaces.

Factors to Consider:  Too much compression of the O-ring.  Extreme temperature.  Material with high compression set properties.  Excessive volume swell.  Incompletely cured elastomer.

Possible Solutions:  Improved gland design for the compound being used.  Low compression set material.  Check material compatibility.

Explosive-Decompression

+ Explosive Decompression

Failure:  The O-ring shows signs of blisters, pits or pocks on its surface.  Absorption of gas at high pressure and the subsequent rapid decrease in pressure.  The absorbed gas blisters and ruptures the elastomer surface as the pressure is rapidly removed.

Factors to Consider:  Rapid pressure changes. Low-modulus/hardness material.

Possible Solutions: Higher modulus/harness elastomer.  Slower decompression.

Extrusion-and-Nibbling

+ Extrusion

Failure: The O-ring develops ragged edges, often on the low-pressure side.  The O-ring appears tattered.

Factors to Consider:  Excessive clearances. Excessive pressure.  Low modulus/hardness elastomer.  Excessive gland fill.  Irregular clearance gaps.  Sharp gland edges.  Improper size O-ring.

Possible Solutions:  Proper gland design. Proper O-ring size.  Decrease clearances.  Higher modulus/hardness material.  Use of a polymer backup ring.

Installation-Damage

+ Installation Damage

Failure:  The O-ring or parts of the O-ring exhibits small cuts, nicks or gashes.

Factors to Consider:  Sharp edges on glands or components.  Improper sizing of elastomer.  Low modulus/hardness elastomer.  Elastomer surface contamination.

Possible Solutions:  Remove all sharp edges. Proper gland design.  Proper O-ring size.  Higher modulus/hardness elastomer.

o-ring-sizing

+ O-ring Sizing / Gland Design

Failure:  The O-ring doesn’t perform as expected.  There is no sign of visual damage.

Factors to Consider:  Incorrect gland design. O-ring size is incorrect.  Hardware is damaged or misalignment.

Possible Solution:  The performance of the O-ring typically can be improved by using the correct O-ring size and/or gland design for the application.

Outgassing

+ Outgassing

Failure:  Failure may be difficult to detect.  The O-ring may exhibit a decease in the size of the cross section.

Factors to Consider:  Improperly cured material. High vacuum levels.  Low hardness or plasticized material.

Possible Solutions:  Make sure all O-rings are properly post cured.  Avoid plasticized materials.

over-compression-update

+ Over Compression

Failure:  The O-ring shows signs of a parallel flat surface to the contact areas. You may notice splits within the flat surfaces

Factors to Consider:  Failure to account for thermal volume changes, chemical volume changes, or excessive compression.

Possible Solutions:  Gland design should take into account how the compound will respond to thermal and chemical environments.

Plasma-Degradation

+ Plasma Degradation

Failure:  The O-ring often exhibits discoloration or a powdered residue on the cross section. There may be erosion in the exposed areas. May be called bloom.

Factors to Consider:  Chemical reactivity of the plasma. Ion bombardment. Electron bombardment. Improper gland design. Wrong material selection.

Possible Solutions:  Plasma compatible material. Minimize the exposed area. Review the gland design.

Spiral-Failure

+ Spiral Failure

Failure:  The O-ring exhibits cuts or marks which spirals around its circumference.

Factors to Consider:  Tight installation, static application. Slow reciprocating speed. Low modulus/hardness material. Irregular O-ring surface finish and/or parting line. Excessive gland surface finish. Inadequate lubrication.

Possible Solutions:  Correct installation procedures. Higher modulus materials. Internally lubed materials. Proper gland design. Use of polymer back up rings.

Thermal-Extrusion

+ Thermal Degradation

Failure:  The O-ring may show signs of radial cracks located on the highest temperature surfaces. Some materials may show signs of softening (a shiny surface as a result of excessive temperatures).

Factors to Consider:  Material thermal properties. Extreme temperature excursions or cycling.

Possible Solutions:  Selection of a material with improved thermal stability. Evaluation of the possibility of cooling sealing surfaces.

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