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O-ring Material Selection

I was helping a client select a plastic material for a piece of industrial equipment. I was involved deeply in the project, assisting them with a variety of plastic components. Selecting the proper material based upon the service requirement is essential for avoiding premature failure. There were six primary plastic components we were focused on, including a housing, a holding tank, gears, and connectors. The material selection went relatively smoothly for these, identifying some materials that offered both performance and cost benefits. Reviewing the assembly design, however, I noticed an O-ring, which would play in integral part in the sealing of the device. I asked my client about this and about material selection for this O-ring. His response was disappointing, but not surprising, “It is just an O-ring – we will just pick something from a catalog”.

While underappreciated, O-rings, play a critical role in many diverse equipment and component applications. An O-ring is a means for closing off a passageway, preventing escape or loss of fluid, either liquid or gas. Failure of an O-ring can have devastating consequences, and as such, the design of the sealing system and the O-ring material selection are very important. In choosing an O-ring material, it is important to consider several factors including applied pressure, the service temperature range, and the chemical being sealed. Oftentimes, balancing the requirements placed on an O-ring can be difficult, and result in a best-case compromise when it comes to material selection. There are many choices for O-ring materials, and they can be manufactured from a wide range of elastomeric materials, both thermoset rubber and thermoplastic elastomers, to provide functional and durable sealing systems. Too often, as typified by the client I discussed above, the number and variety of material selection criteria are often overlooked by system designers, which can lead to premature failure.

In choosing the proper O-ring material, attention must be paid to the following considerations of material characteristic in order to avoid loss of seal and subsequent premature failure of the component:

  • Chemical compatibility
  • Compression set and tension set
  • Stress relaxation
  • Thermal resistance – degradation
  • Cold temperature resilience
  • Abrasion / wear resistance
  • Tear resistance
  • Coefficient of thermal expansion
  • Compressibility / compression modulus

These criteria are different from those used in the selection of other rubber articles, and particular care must be taken in choosing the right O-ring material. Do not underestimate the importance of proper O-ring material selection. Selecting the proper O-ring material can help to avoid component failure.


Rubber Oring material seelction

For more information on how O-rings can fail, see the post O-ring Failure Modes.

Jeffrey A. Jansen

Jeffrey A. Jansen is the Engineering Manager and a Partner at The Madison Group. He was elected as a Fellow of the Society by the Society of Plastics Engineers. Jeff is a proven plastic professional with more than 30 years of experience solving problems and addressing opportunities related to polymeric materials. He specializes in failure analysis, material identification and selection, as well as compatibility, aging, and lifetime prediction studies for thermoplastic materials. Jeff has performed over 5,000 investigations, both for industrial clients and as a part of litigation. He regularly presents seminars and webinars, covering a wide range of topics related to plastics failure, material performance, testing, and polymer technology. Jeff is a graduate of Carroll College and the Milwaukee School of Engineering.