Two methods for assessment of residual life of HK-40 furnace tubes

Two methods were used: one is test-analysis method that is mainly based on the creep rupture tests on postservice specimens. Specimens were taken from the tubes, which had been in service for different times. Kachanov-Robinson's damage summation concept was employed, however with a modified factor K(t_s) to account for prior damage in the specimens. If the foregone total life corresponds with real condition, all of the test data modified by K (t_s) should be distributed uniformly nearby the master curve of the new material. The other is computer simulation method that considers all of the operating conditions that influence the life. The finite element method with iterative calculation was used in the analysis. The variation rates of critical damage element along the wall thickness were determined as a function of the service temperature and current damage. A special program designed based on the method predicts well the residual life of furnace tubes, so long as the maximum depth of critical damage in radius direction of tubes has been detected by ultrasonic techniques.