FATIGUE AND CREEP-FATIGUE CRACK-GROWTH BEHAVIOR OF ALLOY-800 AT 550-DEGREES-C

Fatigue and creep fatigue crack growth behaviour of alloy 800 at 550 d egrees C have been studied to analyse defect assessment in a steam gen erator. Different grades of alloy 800 have been investigated to reprod uce the in service conditions. Fatigue crack growth (FCG) tests were c onducted on CT20 and tubular specimens, then on welded tubes. Furtherm ore the influence of hold times on fatigue crack growth behaviour was studied. The results obtained on material simulating the weld heat aff ected zone are in agreement with the tests conducted on welded tubes. Fatigue crack growth characteristics of aged and cold-worked aged mate rial seem to be slightly improved in comparison with base material. Fi nally a hold time of one minute increases strongly the FCC threshold v alue determined in pure fatigue but has a negligible influence on crac k growth rates.