The Legal History of Determination of Elastomer Shelf Life

Jun 04, 2015 Oil Seals | Materials

Elastomers used in critical applications like seals determine the life of an application. Any defect in the elastomer has a direct impact on the functioning of the application. Breakage or other damage caused to the seal may also cause serious harm to the person handling the machine.

Hence, several rules have been implemented by the Government and other concerned parties regarding shelf life determination and regulation of elastomers used in seals. Shelf life of a product is defined as the time spent between manufacturing and usage/ installation.

We have followed the trail of the different regulations that led to implementation of ARP5316. Documented from the end of World War II to the present day, the history of shelf life-related rules and regulations are listed below.

Stages of Determination of Elastomer Shelf Life: WW-II till Date

elastomers The following is the history of the regulations that were implemented regarding the shelf life of elastomeric seals:

MIL-STD-1523 – Post WW-II, there was a need to determine the age of elastomeric seals used in critical applications. Several studies were conducted to calculate the said age. In 1974, it was concluded that a seal could be used within 12 quarters from the date of curing. This standard was revised to MIL-STD-1523 (A) in 1984, where the usage period was increased to 40 quarters. This standard was cancelled in 1995 since it was found to be limited in scope.

EPRI NP-6608 – This standard was the direct result of the study conducted by Bruce Boyum and Jerral Rhoads. After extensive study, they gathered that the earlier studies were limited. They realized that elastomers reacted differently during the processes of natural and accelerated aging. Furthermore, the fatigue life of some materials increased with time, and of others, fatigue life increased over the same period. They concluded that if elastomeric seals were stored correctly according to the materials used, they could last for a longer period than that dictated by MIL-STD-1523.

AS1933A – AS1933 was used as reference upon cancellation of MIL-STD-1523. This study did not bind aerospace seals by any shelf life regulations. This was an unsure period for the entire industry as manufacturers and buyers alike insisted on shelf life of elastomeric seals.

ARP5316 – Aerospace Recommended Practice (ARP)-5316 is the standard in use as of date, which is issued by Society of Aerospace Engineers (SAE). It was created to provide clarity to manufacturers and buyers. It also provides a clear structure regarding the shelf life of elastomeric seals.

Along with other requirements that are in line with ISO 2230:2002 standards, traceability should also be factored into timely usage of seals. The date of manufacturing of raw materials should be recorded on the day materials are purchased. Complete control of this information will help in correctly determining the shelf life of a product. The date when the seals were cured should be recorded and made available to the buyers as well. Traceability of raw materials should be directly integrated into the workflow. This will help the end user store and use the product correctly.

ISO 2230:2002 – Most manufacturers also comply with ISO 2230:2002 standards. This international guideline has helped optimize the process of storage:

– Proper Storage of Elastomeric Seals

The following rules regarding storage of elastomeric seals should be followed:

– Should be stored at temperatures between –30 °C and 25 °C

– Depending on the location, the level of humidity in the air should not exceed 65-75%. The humidity on the air is irrelevant if the seals are stored in moisture- proof bags or containers.

– The seals should not be exposed to direct sunlight or intense artificial light.

– The seals should not be stored in or around spaces storing ozone- generating equipment.

– The products should also be kept at a safe distance from harmful vapors and products, and electric and magnetic fields.

– The seals should not be stored outdoors at any cost.

– The products should be stored in a way that the ones at the bottom of the pile do not undergo any physical deformities.

Shelf-life Recommendation

If the above storage recommendations are followed, the seals can be stored for four to ten years depending on the materials used.

Most elastomeric materials can be stored for indefinite periods of time. However, as a buyer it important to pay heed to the date of curing of the seals to determine the correct time frame for safe usage of the seals. Since safety of applications and users is dependent on this product, it is essential that the relevant controls and systems be in place for data recording and storage of the products.

Packaging of the products plays an important role in shelf life determination. The reason being that from the date of manufacture to the date of usage, the packaging will have direct influence on the product and its materials. Hence, manufacturers should ensure the packaging is in accordance with the guidelines laid down by ARP5316.