API TR 6J:2000 pdf download

API TR 6J:2000 pdf download.Elastomer Life Estimation Testing Procedures.
Life estimation testing may be considered as the best estimate of long term service life to evaluate the long-term performance of an elastomer in a severe service environment. The basic technique involves collecting time to failure data at elevated temperatures (higher than the maximum anticipated service temperature) and plotting the results on semi-log graph paper. The vertical scale is the log of time to failure and the horizontal scale is the reciprocal of the absolute temperature. Figure 1 shows a typical life estimation plot. Alternately. the time to failure at the service temperature also can be calculated from the appropriate mathematical formula.
4.4 Certain precautions should be exercised when performing accelerated temperature and/or pressure tests. It should be verified experimentally that the failure mechanism (and activation 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 failure criteria. It also may be helpful to test an elastomer material 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.
5 Procedure For Life Estimation Testing Of Elastomers
5.1 The proposed procedure requires the use of an autoclave (a high temperature pressure vessel) to collect time to failure data. Various autoclave and fixture designs can be used. Figure 2 illustrates one design for a life estimation autoclave sealed with standard size 0-rings made from the candidate elastomer. The autoclave should be capable of operation, with a proper safety factor, up to the maximum temperature, pressure and test environment needed for the accelerated test. The internal volume should be appropriately sized to avoid depletion of the test environment during the test: the minimum internal volume should be equal to or exceed 100 cc. The main body and end closures contain 0-ring glands that are fabricated from an appropriate alloy. Typically, a corrosion resistant alloy is used to fabricate the test fixture. Since thermo-chemical degradation of the elastomeric sealing element is of interest, thermo-mechanical effects should be minimized. Therefore, clearances between the end closure and the test vessel bore are minimized to eliminate extrusion (themio-mechanical type failure) of the candidate elastomer.
If additional mechanical protection is required for the 0- ring seal, an anti-extrusion ring (back-up ring) of suitable material can be used. In life estimation testing, only the thermo-chemical effects of a severe environment on a candidate elastomer are evaluated. Actual geometry and thermomechanical effects are best-evaluated using full scale testing.
5.2 The severe service environment is introduced into the test chamber formed by the two end closures. The test vessel is pressurized and heated to a predetermined temperature during each test cycle. The length of the test cycle is established by the testing protocol, i.e., steady state temperature for downhole components or alternating low and high temperature cycles for surface wellhcad equipment. In this example for a surface welihead application, a 72-hour (3-day) test cycle is used. Figure 3 shows how the 3-day test cycle is conducted. The objective of the test sequence is to establish the rate of chemical degradation as a function of temperature.
5.3 The selection of a starting temperature for a life estimation experiment is somewhat arbitrary. A good starting point is an elevated temperature that will consistently give a failure in one or two test cycles. Some experimentation may be required to establish this maximum test temperature. Once the maximum test temperature is determined, lower test tern- pet-attires can be selected, usually in 10°C (18°F) increments. For example, if 450°F is determined to be the maximum test temperature where only one test cycle can be consistently completed, the next lower test temperature would be 432°F. If the experiment follows the Arrhenius relation, two or more test cycles should be completed at 432°F. If two or more test cycles are not achieved at 432°F, the test temperature would be lowered by another 18°F until at least two or more test cycles are achieved consistently.