The 10 most common O-ring failures and what you can do to prevent them from happening.
1. Extrusion and Nibbling
Description: The seal develops ragged edges, generally on the low pressure side, which appear tattered. This condition is more common with high pressure systems
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 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
Description: The seal exhibits parallel flat surfaces corresponding to the sealing surfaces. May also develop circumferential splits within the flattened surfaces.
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
Description: 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.
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
Description: The seal surface exhibits a series of deep, spiral, 45°-angle cuts. This failure is often seen with long-strke, hydraulic piston seals.
Wide clearances in combiniation with side loads
Uneven surface finishes
Elastomer is too soft
Stroke speed too slow-dynamic reciprocating
Increase rigidity and concentricity of metal components
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
Description: 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.
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
Description: 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.
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
Description: 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.
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
Description: 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.
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
Description: The seal or parts of the seal may exhibit small cuts, nicks or gashes.
Sharp surfaces on glands or components
Indequate lead-in chamfer
O-ring too large for gland
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
Description: 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.
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.