Influence of sulfate transients on crack growth in type 304 stainless steel in water at 288 C
- Studsvik Material AB, Nykoeping (Sweden)
During operation of a boiling water reactor (BWR), environmental transients can occur. One such transient is an increased sulfate concentration due to resin intrusions. Sulfate is well known to accelerate the crack growth rate of stainless steel, but the long time influence of sulfate transients on the crack growth rate is more uncertain. Within this work the crack growth rate of heavily sensitized stainless steel was measured in both simulated normal water chemistry (NWC) and simulated hydrogen water chemistry (HWC) environments obtained by adding oxygen to high purity water. Sulfuric acid was added to the environment for a certain period and to a concentration that is comparable with in-plant sulfate transients. Compact Tension (1 inch CT) specimens of sensitized Type 304 stainless steel (UNS S30400) were used and measurements were performed under constant stress intensity at 288 C. Crack growth rates were monitored on-line during testing with a DC potential drop system. The corrosion potential of the specimen was monitored using silver chloride reference electrode. During simulated NWC and HWC a corrosion potential around 0 mV and around {minus}300 mV SHE respectively, was obtained. The crack growth rate did increase after the sulfate transients, but an incubation period was observed. At the time of the increase in the crack growth rate, the inlet and outlet conductivities were back at base line values for simulated BWR-chemistry. Once the crack growth rate increased, it continued to be high for a very long time. Additional sulfate transients after a first one increased the crack growth rate further. The experiment shows that total crack growth in a CT-specimen after a sulfate transient in a low flow autoclave can not be calculated from crack growth values as a function of bulk conductivity. Consideration must also be given to the frequency, strength and magnitude of the transients.
- OSTI ID:
- 203836
- Report Number(s):
- CONF-950816--; ISBN 1-877914-95-9
- Country of Publication:
- United States
- Language:
- English
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