Corrosion Fatigue Crack Initiation in Zr-2.5Nb

ABSTRACTIn-service inspections of Zr-2.5Nb pressure tubes may reveal blunt flaws such as fretting wear or crevice corrosion marks. These flaws pose no immediate threat to the integrity of the pressure tube but may be potential fatigue crack initiation sites. An understanding of the effect of the coolant environment, specifically on fatigue crack initiation, is important in this context. Tests were conducted on notched transverse tensile specimens at 275 and 300 °C with a load rise time between 50 and 3600 s. Current tests investigated the effects of applied loading frequency and hydrogen on fatigue crack initiation. Results have indicated that long rise time and a water environment reduce the time to fatigue crack initiation in non-hydrided and pre-hydrided specimens as compared to tests conducted in air. If enough hydrogen is able to diffuse to the notch during the test, it may also be possible to reach conditions where there is an interaction between corrosion, fatigue and hydride cracking.