1、Elastomer Life Estimation Test i ng Procedu res API TR 6J1 FIRST EDITION, AUGUST 2000 American Petroleum Institute Helping You Get The Job Done Right.“ Elastomer Life Estimation Testing Procedures Upstream Segment API TR 6J1 FIRST EDITION, AUGUST 2000 American Petroleum Institute Helping You Get The
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15、regulation with which this publication may conflict. Suggested revisions are invited and should be submitied to the general manager of the Upstream Segment, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. iii CONTENTS Page 1 SCOPE . 1 2 REFERENCES 1 3 PROBLEMSTATEMENT . 1
16、4 LIFE ESTIMATION TECHNIQUE-OVERVIEW . 1 5 PROCEDURE FOR LIFE ESTIMATION TESTING OF ELASTOMERS . 2 6 SUMMARY . 4 Figures 1-Typical Life Estimation Plot 3 3-TypicaiTestCycle 5 2-0-RingTestFixture . 4 V Elastomer Life Estimation Testing Procedures 1 Scope Estimating the service life of elastomeric sea
17、ling elements used in severe environments, such as encountered in energy exploration and oil/gas production industries, has been extremely difficult. Elastomeric sealing elements are fre- quently exposed to methane, hydrogen sulfide, and carbon dioxide gases, along with crude oil, water and corrosio
18、n inhibiting chemicals. The proposed procedure outlines a tech- nique based on the Arrhenius principle of chemical reaction rates, which permits the life of an elastomeric material to be estimated when exposed to a severe service environment. The actual test procedure must be coordinated and agreed
19、upon between the supplier of the equipment that incorporates the elastomer sealing elements and the end user. The procedure should be based upon a definition of the service conditions and requirements such as: a. Temperature-steady state or a high and low range of service. b. Fluids and gases-stagna
20、nt or flowing. c. Pressure-continuous or a low and high range. d. Chemicals and additives-inhibitors, descalers, acidiz- ing, etc. e. Mechanical requirements-dynamic or static, torque, set- ting force. f. Failure criteria-pressure leakage, loss of mechanical function, inability to set or retrieve. 2
21、 References The following references are recommended as sources of additional information on the life prediction technique dis- cussed above: 1. Vicic, J.C., Testing of Polymers for Oil and Gas Appli- cations, American Chemical Society, Energy Rubber Group, 1984. 2. Abrams, P.I., Kennelley, K.J., Jo
22、hnson, D.V., A User?s Approach to Qualification of Dynamic Seals for Sour Gas Environments, American Chemical Society, Rubber Divi- sion, 1988. 3. Brady, J.E., Humiston, G.E., General Chemistry Prin- ciples and Structure, Third Edition, John Wiley the mini- mum internal volume should be equal to or
23、exceed 100 cc. The main body and end closures contain O-ring glands that are fabricated from an appropriate alloy. Typically, a corro- sion resistant alloy is used to fabricate the test fixture. Since thermo-chemical degradation of the elastomeric sealing ele- ment is of interest, thermo-mechanical
24、effects should be min- imized. Therefore, clearances between the end closure and the test vessel bore are minimized to eliminate extrusion (thermo-mechanicai type failure) of the candidate elastomer. If additional mechanical protection is required for the 0- ring seal, an anti-extrusion ring (back-u
25、p ring) of suitable material can be used. In life estimation testing, only the thermo-chemical effects of a severe environment on a candi- date elastomer are evaluated. Actual geometry and thermo- mechanical effects are bestevaluated using full scale testing. ELASTOMER LIFE ESTIMATION TESTING PROCED
26、URES 3 Log time to failure 1 07 1 06 105 1 04 103 1 o2 Temperature (OK) Figure 1-Typical Life Estimation Plot 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 dur- ing each
27、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 tempera- ture cycles for surface wellhead equipment. In this example for a surface wellhead application, a 72-hour (3-day) test cycle is
28、 used. Figure 3 shows how the 3-day test cycle is con- ducted. 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 estima- tion experiment is somewhat arbitrary. A good starting point
29、 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 maximurn test temperature is determined, lower test tem- peratures can be selected, usually in 10C (1 8F) increments.
30、 For example, if 450F is determined to be the maximum test temperature where only one test cycle can be consistently completed, the next lower test temperature would be 432F. If the experiment follows the Arrhenius relation, two or more test cycles should be completed at 432F. If two or more test cy
31、cles are not achieved at 432“F, the test temperature would be lowered by another 18F until at least two or more test cycles are achieved consistently. At each subsequent test tem- perature, sufficient test runs should be done to obtain test data that are statistically significant. A minimum of three
32、 different test temperatures should be used, but preferably, five tests or more should be done with some replicates. 5.4 Use of the Arrhenius principle in estimating the life of an elastomeric component requires that the chemical process that controls degradation remains constant. If test tempera- t
33、ures are excessive, other reactions may occur and data obtained may lead to erroneous life estimation. Once suffi- cient data have been accumulated, a least squares regression analysis is done and the data plotted to look for any non-lin- earity in the life estimation curve. If a single degradation
34、reaction occurred during testing, the best-fit line should approximate a straight line. For a valid life estimation, the least squares regression analysis on the test data should indi- cate a correlation coefficient greater than 0.90. Once satisfac- tory test data have been generated, the life estim
35、ation line (best fit to data) may be extended to the specified maximum service temperature. An estimate of service life can be read from the vertical scale of the life estimation plot or it can be calculated from the appropriate mathematical formula. 5.5 Proper simulation of the chemical reactions t
36、hat occur between candidate elastomers and the severe service envi- ronment requires a sufficient volume of chemicals must be present to prevent depletion of the reactants. A three (3) day 4 API TR6J1 Full rated pressure at low temperature extreme for 1 hour A test cycle is used so that the candidat
37、e elastomeric material is regularly exposed to fresh chemicals. In service, the elas- tomer may be constantly exposed to a steady stream of fresh chemicals and/or produced fluids/gases or it may only be exposed to stagnant conditions. At the end of the 3-day test cycle, the test vessel is typically
38、rapidly depressurized and purged of the liquid and gas phases. Other decompression cycles can be used with agreement of all concerned parties. Fresh liquid and gas are added and the candidate sealing ele- ments are pressure tested at ambient temperature. For spe- cific applications, other temperatur
39、es below ambient can be used. If the seals hold pressure for one hour without leakage, the test vessel is heated up to the test temperature for another 3-day test cycle. This is repeated until failure is observed. Full rated pressure at low temperature extreme for 1 hour Pressurized service environm
40、ent Test port P 5.6 Some examples of typical failure modes observed for elastomers in life estimation testing are excessive compres- sion set, hardening, cracking and chemical softening. 6 Summary The life estimation procedure outlined above provides a cost effective technique to evaluate the long t
41、erm effects of a chemical environment on a elastomer component. Use of the Arrhenius principle of chemical reaction rates allows an accelerated estimation of the thermochemical degradation of the elastomer in a severe service environment. This evalua- tion technique for studying the long-term effect
42、s of an envi- ronment on an elastomer compound is an alternative to fuii scale, long term testing in the field. I Test - API Member (Check $Ya) Invoice To - U Check here if same as “Ship To” Company: Company: Nammept.: Nammept.: Ship To - (UPS will not deliver to a PO. Box) I Address: StaWrovince: c
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