Why did my O-ring fail?

Chemical attack

Very aggressive chemicals attacked the basic polymer structure of this o-ring. The surface has blisters and cracks with numerous internal fissures and is dimensionally elongated.

O-rings can be damaged by chemical, thermal, or mechanical attack. By understanding the cause of O-ring failure, proper selection of an alternative elastomer or seal design can help improve seal life.

For help analysing a seal failure, call our expert staff on +61 2 9438 1622

 

Chemical Attack

Process chemicals may attack the polymer chain or the elastomer crosslink. The cross linking system holds the polymer chains in place and gives the elastomer resiliency.

Signs of chemical attack are blisters and splits. The surface may be shiny or feel tacky.

Corrective Action

Select a different elastomer compound compatible with the process chemicals (different cross link chemistry)

Thermal attack

Extreme damage to O-ring including compression set, cracking, and splitting.

Thermal Attack

Exposure to temperatures near or above the temperature limit for extended periods of time can result in hardening, showing radial cracks if the elastomer is flexed. Thermal expansion may exceed the groove volume.

Elastomers are rated with an upper temperature, measured in hot, dry air. They may also be over-rated. Process chemicals often result in lowering the functional upper service temperature. Thermal failures should be considered any time an elastomer is used within 25 degrees C of its upper service temperature.

Corrective action

Reduce application temperature, minimise high temperature excursions and select and elastomer with a higher temperature capability

Ask suppliers for long term data (500 hours or longer) on high temperature exposure.

Mechanical attack

This o-ring was pinched or rolled during installation or while in service

Mechanical attack

This O-ring was flattened out and split when a PTFE o-ring was replaced by an elastomer o-ring. PTFE O-rings are designed to be crushed. The elastomer was compressed more than 30%, almost twice the suggested value.

Mechanical Failure

This can occur due to improper seal design or incorrect compound selection. Incorrect installation may result in cuts and spiral failure.

Corrective action

Proper equipment design, groove design and/or proper elastomer installation procedures can minimise the chances of part failure.

Fluid Seals is the Australian Distributor of DuPont™  Kalrez® High Performance Elastomers and Krytox® High Performance Lubricants.