Abstract
Stress corrosion cracking (SCC) is a documented threat to the integrity of carbon steel radioactive waste storage tanks at the Hanford Nuclear Reservation site. Presently, the slow strain rate (SSR) test is the workhorse test technique used for assessing SCC of carbon steels in nuclear waste simulants. The main advantages of the standard SSR technique are that it is relatively rapid, sensitive in detecting SCC, and relatively inexpensive. SSR test results are typically classified as “SCC” or “No SCC”, depending on the ductility parameters from the test and observations of crack features. Occasionally, tests are not easily classified, which results in a third category, “Inconclusive”. Inconclusive results are usually related to variations in ductility parameters compared to the control specimen, or the presence of atypical fracture facets or secondary features on the gage section. Regardless of the cause of the inconclusive result, these tests create uncertainty in assessing susceptibility to SCC. This paper describes the results of a preliminary study undertaken to develop an SCC testing protocol for evaluating inconclusive results. Three alternatives to the standard SSR technique, slower SSR (reduced extension rate), Ripple SSR, and notched SSR, were evaluated. Additionally, SCC evaluations from a crack growth technique using a compact tension specimen were compared to the results of the alternative SSR methods. The study showed that, regardless of the technique evaluated, there will be inconclusive results due to subjective aspects of the post-test evaluation. However, there appears to be a critical potential below which SCC is absent. The value of this potential varies with the test method.
