The atmospherically-induced stress corrosion cracking (AISCC) of austenitic stainless steel type AISI 316L was investigated using a U-bend technique, under conditions relevant for storage of intermediate level radioactive waste drums. The specimens were obtained from an actual '500 litre' drum with a wet-bead blasted surface finish. Using MgCI2 as contaminant salt, it was found that at the characteristic equilibrium relative humidity a threshold deposition for AISCC occurrence is found above chloride-ion contamination levels of 10 and 25 µg cm-2 at 50 and 30 °C, respectively. Higher contamination levels were required to produce cracking at room temperature or with the increase of relative humidity to 60 %. The AISCC severity was related to the spatial characteristics of the electrolyte film. Above 100 µg cm-2, crack depth seems to be controlled by the electrolyte thickness as it determines the diffusion path of oxygen to the cathodic surface. Below 100 µg cm-2, crack depth is affected predominantly by the formation of a discontinuous electrolyte film which results in smaller anodic/cathodic domains. Transition from cracking to pitting corrosion with tunnel appearance was observed as test temperature was decreased from 30 °C to room temperature, except at high chloride deposition levels. The results indicate that AISCC occurrence can be limited by restriction of chloride deposition, control of RH away from the deliquescence point of relevant salts and control of temperature. Using an X-ray diffraction technique, it was found that the drum's surface residual stresses are compressive and would provide a degree of protection against AISCC. However, tensile residual stresses can be found in non-blasted areas and in sections of the drum welds. Exposure of corrosion coupons and U-bend specimens III an underground environment that potentially resembles a geological disposal facility did not cause any significant pitting or AISCC after 1.75 years of exposure. This was correlated to a low chloride deposition and a high average RH that would have maintained the hygroscopic deposits in a dilute condition.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:579513 |
| Date | January 2011 |
| Creators | Albores-Silva, Octavio E. |
| Publisher | University of Newcastle Upon Tyne |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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