The prematurely failing O-ring is a common problem that can be frustrating at best and nearly catastrophic at worst. O-ring seals fail for a variety of reasons that can be difficult to ascertain once the damage has been done.
Use this checklist to troubleshoot the cause of your o-ring failures and you may just extend the life of your o-ring and equipment in the process.
Small cuts or even gashes in the o-ring is a good indication of installation damage. This typically occurs when the o-ring is not the correct size, causing sharp edges to damage the seal.
Solution: Remove all sharp edges and reevaluate the size of o-ring needed. Another solution may be to use a seal with a greater hardness.
Twisting damage, or spiral twisting failure, is indicated by cuts that spiral, or twist, around the ring. This can happen if the seal is too tight or the surface finish is blemished, irregular, or rough. Other causes can be that the o-ring is too wide or there is not enough lubricant.
Solution: Following correct installation procedures is the main line of defense. It’s also important to make sure that there is sufficient lubricant and the gland design is correct and free of imperfections.
Abrasion occurs through rough sealing surfaces or the environment has abrasive particles. Other contributing factors can be an insufficient surface finish on the seal as well as excessive temperatures. When this happens the seal will show a flat surface parallel to the motion.
Solution: Eliminate any abrasive components and make sure only the recommended gland surface finishes are being used.
Plasma degradation can be identified by discoloration and a powdery surface. It is possible for there to be some erosion of the seal as well. Most often this is due to incompatible materials and/or the wrong design.
Solution: Use a plasma compatible seal and make sure the gland design is correct.
Radial cracks will appear on the seal near the higher temperature surfaces, also known as thermal degradation. Other signs of thermal degradation are a softening of the elastomers, which will cause a shiny surface area. This happens with the temperature becomes excessive or the thermal properties of the seal are not correct for the application.
Solution: Choose a seal with the correct thermal stability rating.
Blistering, cracking, and discoloration are all signs of chemical degradation. This occurs when the chemical environment is not compatible with the seal.
Solution: Select an o-ring that is more chemically compatible with the environment.
When the o-ring does not perform the way it’s supposed to but there is no visible signs of damage it most likely means that the wrong o-ring has been installed. This could be that the o-ring is simply the wrong size or it’s the incorrect groove design.
Solution: Reevaluate the o-ring needed. Often times, taking a quick look at an o-ring design guide will help determine the right one for the job.
If the o-ring shows parallel flat surfaces or you see splits within the flattened surfaces then there is most likely over compression. This typically occurs when thermal or chemical volume changes were not taken into consideration and therefore the wrong design was chosen.
Solution: Choose a gland design that is compatible with both the thermal and chemical environments.
When the seal begins to blister or develop pits on the surface it’s usually due to rapid changes pressure changes. Other indications of a problem may be the absorption of gas at a high pressure followed by a rapid decrease of pressure. The absorbed gas is what causes the seal to blister and then rupture as the pressure decreases.
Solution: Using an elastomer with a higher degree of hardness as well as decreasing the release of pressure will help prevent explosive decompression.
Compression set occurs when the o-ring shows a flattening of a cross-section of the ring. This can happen when there is excessive compression, temperature, or the elastomer was not cured completely before it was used. Other factors can be using an elastomer with a high compression set or excessive volume swell in the chemical.
Solution: Try using a low compression set elastomer. Make sure the gland design is the correct one for the application and that the material is compatible as well.
When outgassing is an issue, there is rarely a sign of it when looking at the seal. If there is any outward indication at all it will be a decrease in the cross-sectional size of the o-ring. Outgassing is usually related to an elastomer that has been improperly cured. It can also be caused by high vacuum levels or an elastomer with a lower grade of hardness.
Solution: Making sure that all seals are cured correctly and avoiding plasticized seals is the best response to prevent, or at least reduce the potential for outgassing.