Elastomer shelf life: aged junk or jewels?

The shelf life of elastomeric products used in the nuclear industry is typically based on military standards (MIL-HDBK-695C or MIL-STD-1523A). Recently, data became available on naturally aged O-rings that were over 30 years old. An evaluation of this data is presented to demonstrate the conservatism of current guidelines. The test data indicate that typically hardness increases, tensile strength increases, elongation decreases and compression set increases over a period of time. It is concluded that the shelf life for elastomers can be substantially longer than that specified by MIL-HDBK-694C and MIL-STD-1523A, provided that the elastomers are stored in a controlled environment and are purchased from a reputable manufacturer who maintains a quality-controlled manufacturing process to ensure repeatability of elastomer formulation.<>