Rubber seals such as O rings are developed and manufactured to last. We can select materials for optimal performance for the environment they’re going to be in, such as heat resistance or chemical compatibility. However, as all polymers are unique in their make up and structure, using the right material for the application is crucial.

Understanding what can cause chemical degradation, and how different materials react to certain chemicals, can avoid costly failures later down the line. Here’s what you need to know about chemicals and their effects on your rubber components and seals.

What causes chemical degradation?

Some chemicals will react with certain elastomers, if those materials are not resistant enough to the chemicals they are exposed to. This can cause a range of problems, from an increase in cross link density, leading to a hard, brittle seal, to chain scission, resulting in reduced strength.

In some situations, the chemical or elements of it can actually ingress into the seal itself. This is often caused by the chemical being too similar to the material used in the elastomer, effectively allowing the media to be soaked up by the seal.

Having the wrong type of seal for the job increases the risk of a chemical attack, and it’s not just a failed seal you may have to deal with. Seal failure and associated chemical ingress into other parts of the assembly, may lead to direct loss or damage to expensive machinery, not to mention process downtime within the operation.

How to know if your O ring has suffered a chemical attack

The first way to identify chemical degradation in O rings is to take a visual appraisal of the component. There are several tell tale symptoms of a chemical attack, including:

• Cracking and / or blistering
• A change in hardness
• Discolouration
• Swelling, either localised or across the whole seal

Some of these symptoms can be caused by other issues, so it’s important to eliminate these or confirm chemical presence as soon as possible.

How to prevent a chemical attack

Choosing the right elastomer for the job is key to preventing any further chemical attack. Switch to an elastomer with proven resistance against the chemicals you know to be present in the environment.

Chemical attack is accelerated in elevated temperatures and when the seal is stressed, for example when its been stretched or squeezed excessively. This means that a material which, at first, seemed compatible suddenly becomes incompatible due to the forces it is placed under.

The best way to prevent chemical attack is to consult with an expert when making your material choice. To be sure that you’re getting the right elastomer for the job, chemical compatibility testing can be undertaken to help with your selection process.

Which elastomers offer the best chemical resistance?

The resistance of elastomers depends on the type of chemicals they will be coming into contact with. For example, if you’re using acetaldehyde in your operations, silicone and EPDM offer excellent resistance, whereas fluorocarbon, FFKM and polyurethane will fail. Nitrile and fluorocarbon would be a good choice for calcium bisulfide, whereas EPDM and natural rubber would not.

For help selecting the right type of material for your application, talk to our team.