Atmospheric Stress Corrosion Cracking Susceptibility of Welded and Unwelded 304, 304L, and 316L Austenitic Stainless Steels Commonly Used for Dry Cask Storage Containers Exposed to Marine Environments

摘要

This report documents information on the susceptibility to atmospheric stress corrosion cracking of welded and unwelded 304, 304L, and 316L austenitic stainless steels commonly used for dry storage containers exposed to marine environments. Standard U-bend specimens were exposed to both salt spray and salt fog conditions at temperatures ranging from 25 to 176 degrees C and varying relative humidity. The first test conducted was a salt spray test to scope out material and residual stress effects. This deliberately conservative test resulted in extensive cracking and corrosion as was observed in all the 93 and 176 degrees C Ubends in as early as 1 month after exposure. Salt spray tests are non-prototypical since deposition of salt on dry casks is in the form of a dry aerosol; hence, the first test was not suitable for evaluation of stress corrosion cracking susceptibility of austenitic stainless steels in coastal atmospheres. The second test conducted, the salt fog test, was expected to closely simulate field conditions around dry cask containers, and resulted in stress corrosion cracking and pitting corrosion in all the 43 degrees C specimens. Corrosion developed after 4 weeks in the 304 and 304L specimens, and after 32 weeks in the 316L specimen. This suggests that the alloy composition plays a role in stress corrosion cracking susceptibility. Cracking was mainly transgranular with sections of intergranular branching.