API TR 6J1:2000 pdf download.Elastomer Life Estimation Testing Procedures
3 Problem Statement
3.1 Traditional methods of evaluating elastomers used for sealing elements involve the use of ASTM or other standard immersion-type tests. In these techniques, samples of the candidate elastomeric material are immersed in the antici- pated environment for a specified time period in the free state. Immersion times can vary from hours, to weeks, to months. The samples may be in a pressurized or unpressur- ized environment. The physical properties before and after immersion are compared and a judgment is made as to the suitability of the elastomer for use in the service environ- ment. The elastomeric material is generally not tested in its end use geometry (form) and not confined to a seal gland. In a properly designed seal gland, minimal seal surface area is exposed to the severe environment, and the gland physically limits the swell of the sealing element within the gland. The use of an immersion testing technique for retained physical properties does not answer the question of how long the elas- tomeric sealing element will function as a seal in a severe environment. Many sealing elements used in the energy exploration and oil/gas production industries are expected to remain serviceable (not leak) for up to 20 years in a severe service environment.
3.2 Traditional immersion tests for retained physical prop- erties have a role in the initial screening of suitable candidate elastomeric materials. A material would not be selected for service, which was severely attacked and deteriorated by the service environment in an immersion test. However, some degradation of physical properties (stress-strain) and volu- metric swell can be tolerated. It should also be noted that cer- tain elastomeric materials may sustain minimal property degradation in an immersion test, but they still may not be suitable for long-term sealing service. This is because they exhibit excessive creep or stress relaxation at high pressures and/or temperature.
4.4 Certain precautions should be exercised when perform- ing accelerated temperature and/or pressure tests. It should be verified experimentally that the failure mechanism (and acti- vation energy) does not change with elevated temperatures or pressures. In addition, it must be recognized gas diffusion may occur through an elastomer seal at an accelerated rate and this must be properly accounted for if this is used as fail- ure criteria. It also may be helpful to test an elastomer mate- rial with known field performance as a reference for comparison. Stagnant fluids and gases may give better or worse life estimation than if the fluids are periodically refreshed.