Shelf life of an O Ring
Shelf Life – What & Why
Shelf Life – noun – the length of time for which an item remains usable, fit for consumption, or saleable
The rubber industry generally uses old US military specs and current SAE Aerospace recommendations to calculate elastomer and O-Ring shelf life. We use quarter year units presented as 1Q20 meaning first quarter of year 2020. Since the actual manufacturing cure date can occur anytime within the 3 month quarter, the expiration time does not begin until after the first fully complete quarter. An elastomer cured on November 15th 2020 would have a cure date presented as 4Q20 but would not begin ageing for expiration date purposes until January 1 st (1Q21). Hence a 3 year life would expire Jan 1 st 2024 (1Q24).
Rubber life is by no means an exact science because storage and handling has a significant impact on some products. For a more relatable example, if milk has an expiration date of today, what time does it expire? Could it spoil earlier? Could it be safe to drink past the expiration date? As a result many suppliers will label shelf life and expiration to customer request based on their expertise and judgement of their own storage, handling and usage application judgement.
A Brief History
Age control of elastomeric seals and assemblies started after World War II on hydraulic, fuel and lubrication seals on aircraft.
- 1958 – ANA Bulletin 483, first document relating to age control released. A compilation of several studies on age control done since WWII
- 1973 – MIL-STD-1523 released after several more studies and papers. This spec gave a maximum shelf life of 12 quarters
- 1984 – MIL-STD-1523A released and shelf life extended to 40 quarters
- 1995 – MIL-STD-1523A cancelled and AS1933 cited as a potential replacement. However, as AS1933 deals specifically with rubber hose and does not deal directly with the concerns of the seal industry
- 1998 – ARP5316 was written to provide a foundation upon which seal manufacturers, distributors, and users could generate realistic shelf life criteria
Here at O Rings Limited we use ARP5316 in line with Trelleborg Sealing Solutions of whom we are a Partner / Distributor.