Creep-Damage in Pressure Components Experiencing Follow-Up
A simple method for estimating creep-damage in pressure components experiencing elastic or creep follow-up is presented. The theoretical formulation essentially relates the multiaxial relaxation process that exhibits follow-up to the traditional uniaxial stress-relaxation model. The resulting mixed-mode response is expressed in the generalized local stress-strain plot. The follow-up parameters are then determined by utilizing the slope of the relaxation-response in the generalized local stress-strain plot. Finally, a procedure for partitioning the accumulated fellow-up damage into Ioad-controlled and deformation-controlled contributions is discussed. The method is applied to a typical elevated-temperature piping system configuration that exhibits follow-up potential.
References
Criteria of the ASME boiler and pressure vessel code for design by analysis in sections III and VIII, division 2. Pressure vessels and piping: design and analysis, 1, Decade of Progress, ASME, 1972.
D. BURGREEN, Design methods for power plant structures, C. P. Press, 1975.
D. L. MARRIOTT, Evaluation of deformation or load-control of stresses under inelastic conditions using elastic finite element stress analysis, ASME PVP, 136, Pittsburgh 1988.
L. ROBINSON, Stream-piping design to minimize creep concentrations, Trans. ASME, 77, 1147, 1955.
J. T. BOYLE and J. MITCHELL, The geometric nature of elastic follow-up, ASME PVP, 136, Pittsburgh 1988.
R. L. ROCHE, Estimation of piping elastic follow-up by using conventional computations, Int. J. Pres. Ves. and Piping, 26, pp. 53-78, 1986.
A. K. DHALLA, A simplified procedure to classify stresses for elevated temperature service, ASME PVP, 120, San Diego 1987.
R. SESHADRI, Estimation of multiaxial stress-relaxation using isochronous curves, ASME PVP, 135, Pittsburgh 1988.
R. SESHADRI, The generalized local stress-strain diagram for estimating follow-up. ISE Research Report, 88-03,1988.