A research project was conducted to develop and validate an improved, analytical life prediction method for high-temperature turbine and valve studs/bolts. The life prediction method used the two-parameter creep equation, an incremental calculation procedure and a strain hardening flow rule. The failure criterion was an accumulated inelastic or creep strain limit of 1 percent. The life prediction procedure recommends the use of the service history of operating temperature, number/stress level of tightenings, cycle time, etc., to calculate the stress relaxation behavior. Life assessment uses the measured bolt length to calculate the accumulated creep strain. The link between the current condition, i.e., accumulated creep strain, and the remaining creep life, i.e., time to accumulate 1 percent strain, is obtained by a prediction of the future creep strain accumulation under the intended loading cycle(s) imposed during future operation. In order to validate the approach, the calculated results were compared to the results of uniaxial stress relaxation testing, bolt model testing, and service experience. The analytical procedure coupled with other industry wide NDE and measurement procedures is expected to provide broad guidelines to utilities for bolting life assessment.

Branch, G. D., Draper, J. H. M., Hodges, N. W., Marriott, J. B., Murphy, M. C., Smith, A. I., and Toft, L. H., 1973, “High Temperature Bolts for Steam Power Plant,” International Conference on Creep and Fatigue in Elevated Temperature Applications, Proc. Inst. Mech. Eng., pp. 192.1–192.9.
Bolton, J., 1995, “Design Considerations for High Temperature Bolting,” Performance of Bolting Materials in High Temperature Plant Applications, The Institute of Materials, London, UK, pp. 1–14.
Ellis, F. V., Sielski, D. R., and Viswanathan, R., 1998, “Guidelines for Life Assessment of High Temperature Bolting,” Fitness-for-Service Evaluations in Petroleum and Fossil Power Plants, ASME, New York, NY, pp. 119–127.
EPRI, 1999, High Temperature Bolting Life Prediction and Life Assessment, TR-113529, EPRI, Palo Alto, CA.
Ellis, F. V., and Sielski, D. R., 2000, “Mechanical Properties of Ex-Service Bolts,” Service Experience and Fitness-for-Service in Power and Petroleum Processing, ASME, New York, NY, pp. 311–318.
Ellis, F. V., Tordonato, S., and Viswanathan, R., 1998, “Prediction of Cyclic Stress Relaxation for 1CrMoVTiB,” Fatigue, Fracture, and High Temperature Design Methods in Pressure Vessels and Piping, ASME, New York NY, pp. 175–182.
Ellis, F. V., and Tordonato, S., 1999, “Ca´lculation of Stress Relaxation Properties for Type 422 Stainless Steel,” Fracture Mechanics: Design and Analysis of Pressure Vessels, Heat Exchangers, and Piping; and Fitness for Service. ASME, New York NY, pp. 395–403.
Sielski, D. R., and Steakley, M. F., 1998, Unpublished Research, Tennessee Valley Authority, Chattanooga, TN.
de Witte, M., and Stubbe, J., 1985, “Failure Mechanisms and Practical Approach for the Following Up of High Temperature Turbine Bolts,” Proc. International Conference on Remanent Life: Assessment and Extension, EUROTEST, Brussels, Belgium.
Ellis, F. V., Roberts, B. W., Steakley, M. F., and Hilton, S. O., 1992, “Application of Creep Swelling Data In Life Assessment of High Temperature Piping,” Creep:Characterization, Damage and Life Assessment, ASM International, Materials Park, OH, pp. 481–489.
NRIM, 1997, “Data Sheets on The Elevated-Temperature Stress Relaxation Properties of 1Cr-0.5Mo-0.25V Steel and 12Cr-1Mo-1W-0.25V Steel Bolting Materials for High Temperature Service,” NRIM Creep Data Sheet No. 44, National Research Institute for Metals, Tokyo, Japan.
General Electric, 1979, “Valve Studs—Tightening, Inspection and Replacement Recommendations,” TIL-891.
, and
, “
Analysis of Reloading Stress Relaxation Behavior with Specified Reloading Time Intervals for High Temperature Bolting Steels
Trans. Nat. Res. Inst. Metals
, No.
, pp.
Townsend, R. D., 1995, “Performance of High Temperature Bolting,” Performance of Bolting Materials in High Temperature Plant Applications, The Institute of Materials, London, UK, pp. 15–40.
Mayer, K. H., and Konig, H., 1992, “New Materials for Advanced Steam Turbines; Volume 4: Testing of Superalloy Bolt Materials for Advanced Power Plants,” EPRI TR-100979, Vol. 4, RP1403-15 Final Report, EPRI, Palo Alto, CA.
Ellis, F. V., 2000, “Heat-to-Heat Variability in Stress Relaxation of Type 422,” Fitness for Service, Stress Classification and Expansion Joint Design-2000, ASME, New York, NY, pp. 43–52.
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