Many items have a limited shelf-life, from dairy products to medications to seals?
Depending on the type of material your seal is made of, it can have a limited shelf life.
What Is Shelf-Life?
Shelf-life refers to how long a seal can be left in storage before it is no longer appropriate for use. Some polymers and elastomers have a limited shelf life, which basically means there is a limit to how long they can be left on the shelf and still be used.
Issues Behind Shelf-Life
Shelf-life becomes a problem when seals are made of a material that can degrade due to atmospheric
exposure or can be chemically unstable. As an example, consider how some plastic shopping bags will become brittle and harden as they are left out in the sun. Exposure to UV light in this case, sunlight can cause some materials to begin to degrade. While that is great for a product that is used maybe a few times and disposed of, it isnt so great when it comes to a seal that you are depending on to protect your equipment. This is where shelf-life can become a concern.
Most shelf-life issues occur with elastomeric seals which can be sensitive to UV and ozone. For these
materials, excessive exposure to UV and ozone can cause embrittlement and premature aging, which
compromises the performance of the seal. Two other potential issues are exposure to high
temperatures or excessive humidity.
Storage to Prolong Shelf-Life
The recommended conditions for polymer elastomeric seal storage rooms are based on the SAE
ARP5316 standard: no equipment that can generate ozone should be present, no exposure to direct
sunlight or very intense artificial light, temperatures should be kept below 100°F, and humidity should
be less than 75% unless the seals are stored in moisture proof packaging.
When these types of simple, common sense conditions are followed, shelf-life is practically unlimited for many elastomers and all polymers.
Approximate Shelf-Life for Seal Materials
The main exceptions to unlimited shelf-life are NBR, HNBR, Polyacrylate, and Chloroprene, which have a recommended shelf life of 15 years; Polyurethane, which has a recommended shelf life of 3 years; and Styrene Butadiene, which has an average shelf life of 5 years.
One of the major benefits of polymer seals over elastomeric seals is the
unlimited shelf-life of polymer seals.
Flourocarbons like PTFE have an unlimited shelf life, as do fluoroelastomers like FKM and materials like PEEK. As a matter of fact, one of the major benefits of polymer seals over elastomeric seals is the unlimited shelf-life of polymer seals.
When selecting a seal, remember to check the expected shelf-life of the material and verify that it will
be possible to store seals in accordance with common sense. If shelf-life is a major concern, then
polymer seals should be seriously considered.