Shelf Life of an O-Ring
All elastomers change gradually with age. Some change more rapidly than others. These changes lead to alteration in the physical properties that can cause detrimental effect. Therefore, Shelf life of an O-Ring is an important factor that has to be considered.
To meet the needs of sealing industry, in 1998, SAE (Society of Aerospace Engineer) developed ARP5316 to provide a basis for establishing of elastomer Shelf life. The history of Shelf life and age control of elastomers dates back to World War II on hydraulics, fuel, and lubrication seals on aircraft. In 1958, compilation of several studies on age control was done and the first document on age control was released. In 1973, MIL_STD1523 released more papers and gave twelve quarters as maximum Shelf life. In 1984, 40 quarters were released. However, in 1995, this standard was cancelled when the release of ASI1933 was issued.
Recommended Shelf life of an O-Ring as per ARP5316
➢ Butyl rubber, Isobutylene isoprene
➢ Ethylene propylene
➢ Fluor silicone
- 15 YEARS
➢ Ethylene acrylic
➢ Hydrogenated nitrile
- 5 YEARS
➢ Natural rubber
Cure date is the basis of determining the age of O-Rings. Based on the Cure date specified by the supplier, verification of the remaining Shelf life of O-Rings can be obtained. ARP5316 does not mention the quarter. Hence, ‘time of manufacture’ is taken as the last date of quarter of Cure. The expiration date can be determined by adding Shelf life to the Cure date.
Proper storage is essential in extending the Shelf life of O-Rings. Storage life is the maximum period of time, starting from the time of manufacture, that an elastomeric seal element, appropriately packaged, may be stored under specific conditions, after which time it is regarded as unserviceable for the purpose for which it was originally manufactured.
General requirements of the storage are as follows:
▪ Temperature around 23° C.
▪ Exclusion of direct sunlight.
▪ Dry environment and exclusion of contamination.
▪ Avoid contact with fluids.
▪ Protect against artificial light containing UV radiation.
▪ Protection from radioactive and ozone generating electrical devices.
▪ Store parts without tension and never hang O-Rings.
The packaging also forms an integral part of storage procedures. Individual packaging of rubber seal protects them and maintains batch traceability. Free access of air should be avoided. The packing materials obtained should preferably be opaque and free from any film containing plasticizers. The product should be packed in such a manner that distortion is avoided. Some suitable materials are polyethylene coated Kraft paper, aluminum foil/paper/polyethylene laminate and opaque polyethylene film.
Correct packaging of stored articles not only assure maximum Shelf life, but also avoids many problems associated with unavoidable environmental changes, condition and rotation of these stocks will keep this harmful effects to minimum. Hence, this is an essential aspect to be considered.