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The 10 most common O-ring failures and what you can do to prevent them from happening.

1. Extrusion and Nibbling

extrusion or nibblingDescription: The seal develops ragged edges, generally on the low pressure side, which appear tattered. This condition is more common with high pressure systems

Contributing Factors:                  Suggested Solutions:
  • Excessive clearances
  • Excessive System Pressure
  • Irregular clearance gaps due to eccentricity
  • Sharp groove edges
  • Low-modulus/ low-hardness elastomer
  • Softening of elastomer due to fluid incompatibility
  • Excessive gland fill
  • Expansion of cylinder wall due to pressure
  • Decrease clearances
  • Decrease system pressure if possible
  • Use back-up ring
  • Increase rigidity and concentricity of metal components
  • Break edges of groove to minimum of .004”(0.10mm)
  • Use higher –modulus/higher-hardness elastomer
  • Use more chemical compatible elastomer
  • Increase groove width or change O-ring size
  • Stiffen cylinder wall to limit expansion

 

2. Over Compression

over compressionDescription: The seal exhibits parallel flat surfaces corresponding to the sealing surfaces. May also develop circumferential splits within the flattened surfaces.

Contributing Factors:                  Suggested Solutions:
  • Excessive compression squeeze
  • Elastomer with poor compression set properties
  • Elastomer with inadequate heat resistance
  • Elastomer that swells excessivel in system fluid
  • Improperly cured part used
  • Use smaller o-ring or adjust gland dimensions
  • Use material with better compression set resistance
  • Use more heat resistant elastomer
  • Use more chemically resistant elastomer
  • Check cure state of parts prior to installation

 

3. Heat Hardening/Thermal Degradation

heat hardeningDescription: The seal may exhibit radial cracking on the highest temperature surfaces, often accompanied by the flattening of the seal characteristic of over-compression. Certain elastomers may exhibit signs of softening, such as a shiny surface.

Contributing Factors:                  Suggested Solutions:
  • Thermal properties of elastomer
  • Excessive temperatures, temperature excursions or temperature cycling
  • Select more heat-resistant elastomer
  • Select elastomer containing antioxidants
  • Consider possibility of cooling sealing surfaces
  • Increase thermal mass to dampen temperature cycling or excursions
  • Change the position of the gland away from heat source

 

4. Spiral Failure

spiral failureDescription: The seal surface exhibits a series of deep, spiral, 45°-angle cuts. This failure is often seen with long-strke, hydraulic piston seals.

Contributing Factors:                  Suggested Solutions:
  • Eccentric components
  • Wide clearances in combiniation
        with side loads
  • Uneven surface finishes
  • Inadequate lubrication
  • Elastomer is too soft
  • Stroke speed too slow-dynamic reciprocating
  • Increase rigidity and concentricity
        of metal components
  • Decrease clearances
  • Machine metal surfaces to 10 to 20µinch surface finish
  • Specify an external lubricant or use an internally lubricated material
  • Use a higher durometer material
  • Increase stroke speed or use D-ring instead of O-ring

 

5. Chemical Degradation

chemical degradationDescription: The seal may exhibit many signs of degradation including blisters, cracks, voids or discoloration. However, in some cases the degradation is only detectable by measurement of physical properties.

Contributing Factors:                  Suggested Solutions:
  • Incompatibility with chemical environment
  • Use more chemcially resistant elastomer
  • Use PTFE encapsulated O-rings
  • Decrease temperature that O-ring sees, as higher temperatures accelerate chemical degradation.

 

 6. Explosive Decompression

explosive decompressionDescription: Explosive decompression results when high-pressure gases are absorbed by the seal, and then, as the pressure is rapidly dropped, the expanding gasses are trapped in the micropores of the elastomer, causing surface blisters and ruptures as they escape. The effected seals will exhibit random short splits or ruptures deep into the seal cross-section. When first removed the surface may also be covered with small blisters.

Contributing Factors:                  Suggested Solutions:
  • Rapid pressure drop from high pressure
  • Low-modulus/low- hardness ealstomer
  • Slow the release of system pressure
  • Specifity a higher-modulus/higher-hardness material
  • Specify a decompression-resistant material

 

7. Abrasion 

abrasionDescription: Abrasion occurs only with dynamic seals-seals involved with a rotary, oscillating or reciprocating motion. The seal or parts of the seal exhibit a single flat surface parallel to the direction of motion. Loose particles and scrapes may be found on the seal surface.

Contributing Factors:                  Suggested Solutions:
  • Rough sealing surfaces
  • Sealing surfaces too smooth to allow for adequate lubriation
  • Process environment containing obrasie particles
  • Use recommended gland surface finishes
  • Eliminate abrasive components or protect seal from exposure to them

 

 8. Plasticizer Extraction

plasticzer extractionDescription: Seen primarily in fuel systems, plasticizer extraction is characterized by a loss of volume or weight of the seal. It is often difficult to detect with only a visual inspection.

Contributing Factors:                  Suggested Solutions:
  • Heavy use of plasticizers to achieve
  • Exposure to organic solvents compatible with plasticizers used
  • Switch to elastomer with low-temperature properties to plasticizers aren’t needed
  • Change plasticizers used to ones less compatible with process fluids

 

 9. Installation Damage

installation damageDescription: The seal or parts of the seal may exhibit small cuts, nicks or gashes.

Contributing Factors:                  Suggested Solutions:
  • Sharp surfaces on glands or components
  • Indequate lead-in chamfer
  • O-ring too large for gland
  • Low-modulus/Low-hardness elastomer
  • Break all sharp metal edges and cover threads with tubes or tape for installation
  • Provide 15° lead-in chamfer of adequate length so O-ring sees only chamfer
  • Review gland and o-ring design per recommended design standards
  • Specify a higher-modulus/higher-hardness material

 

 10. Weather/Ozone Cracking

weather ozoneDescription: Occurring in seals exposed to Ozone, UV radiation or other air pollutants. Weather or ozone cracking is characterized by small surface cracks perpendicular to the direction of stress.

Contributing Factors:                  Suggested Solutions:
  • Exposure to ozone, UV radiation or other air pollutants
  • Excessive seal stretch (>5% ID stretch)
  • Select more ozone-and UV-resistant elastomer
  • Apply anti-ozonant or wax coating to seal
  • Modify the design to avoid the damaging exposure
  • Modify design to reduce stretch to less than 5%

 

For more information related to O-ring sizes and materials please visit our O-rings product page. And for any technical information related to housing and more, please check out our O-ring design guide