The effect of stress intensity factors (K) at the intergranular attack and stress corrosion crack (IGA/SCC) tips on the IGA/SCC propagation behavior of steam generator (SG) tubing was studied under accelerated test conditions. Values of K at the IGA/SCC crack tips were calculated using the statically indeterminate model. Based upon analysis of those factors, the double-cantilever beam (DCB) and SG model boiler tests were carried out to evaluate the effect of stress intensity on IGA/SCC crack propagation. K at the crack tips increased with increasing crack length. For a long crack, K decreased with an increasing numbers of cracks. However, for a short crack, K decreased slightly with an increasing number of cracks. DCB test results showed the IGA/SCC crack velocity of alloy 600 (UNS N06600) increased gradually with increasing K in the range from 15 MPa√m to ~ 60 MPa√m. This is the range relevant to IGA/SCC crack tips of typical SG tubes under operating conditions of pressurized-water reactors. Metallographic examination of tubes removed from the SG model boiler, fouled with 10 ppm sodium hydroxide (NaOH), showed IGA/SCC propagation rates were almost constant in the tested range of K.

Subject
Stress intensity, Oxide formation, Tubes, Notches, Walls, Oxide films, Crack propagation, Stress cracking, Crevices, Crack velocity, Boilers, Alloys, Cracks
Keywords:
alloy 600, crack growth rate, double-cantilever beam, high-temperature water, intergranular attack, oxide film, statically indeterminate model, stress corrosion cracking, stress intensity factor
NACE International
1999
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