Environment Assisted Fatigue – Experimental Challenges and Solutions

The design fatigue curves applied for safety class 1 components in NPP’s are based on an experimentally determined strain-life fatigue data, the resulting ε-N reference curves and transferability margins. To account for detrimental effects of coolant water environment, penalty factors (Fen) are obtained by comparing fatigue lives in air and environment. To avoid bias in comparison, the same fatigue testing procedures according to ASTM E606 would be preferred in both environments. However, modified EAF test procedures were developed when direct control of strain in the specimen gauge section was not possible. This paper introduces and discusses commonly used experimental approaches for conducting (directly or remotely) strain-controlled fatigue tests in simulated LWR coolant water environments. At or near gauge section remotely controlled and tubular specimens have been successfully used to determine penalty factors for fatigue usage in environment, but variation and uncertainties related to experimental methods used for collecting the data cannot be completely excluded. The challenges and solutions adopted during latest 20 years in Finland are explained.