Fatigue crack initiation in carbon and low-alloy steels in light water reactor211 environments: mechanism and prediction

摘要

Section 111 of the ASME Boiler and Pressure Vessel Code specifies fatigue design211u001ecurves for structural materials. The effects of reactor coolant environments are 211u001enot explicitly addressed by the Code design curves. Recent test data illustrate 211u001epotentially significant effects of light water reactor (LWR) coolant environments 211u001eon the fatigue resistance of carbon and low-alloy steels. Under certain loading 211u001eand environmental conditions, fatigue lives of test specimens may be shorter than 211u001ethose in air by a factor of (approx)70. The crack initiation and crack growth 211u001echaracteristics of carbon and low-alloy steels in LWR environments are presented. 211u001eDecreases in fatigue life of these steels in high-dissolved-oxygen water are 211u001ecaused primarily by the effect of environment on growth of short cracks < 211u001e100 (micro)m in depth. The material and loading parameters that influence fatigue 211u001elife in LWR environments are defined. Fatigue life is decreased significantly 211u001ewhen five conditions are satisfied simultaneously, viz., applied strain range, 211u001eservice temperature, dissolved oxygen in water, and S content in steel are above 211u001ea threshold level, and loading strain rate is below a threshold value. 211u001eStatistical models have been developed for estimating the fatigue life of these 211u001esteels in LWR environments. The significance of the effect of environment on the 211u001ecurrent Code design curve is evaluated.