Evaluation method of corrosion lifetime of conventional stainless steel canister under oceanic air environment

摘要

Natural exposure and accelerated corrosion tests of conventional stainless steels for canisters of Types 304, 304L, and 316(LN) for concrete casks were conducted using several test specimens and 1/5 scale canister models. The welding residual stress of a full-scale model canister was also measured and the lifetime of sealability of canisters against corrosion evaluated. The maximum pitting rate and crevice corrosion rate of Type 304 were approximately 20 and 30 μm/year. Many SCC in the 4 Point Bending (4PB) test specimens were found to initiate from the bottom of the corrosion area by pitting or crevice corrosion. The SCC propagation rates in Types 304 and 304L under natural conditions were around 1.2E-12 to 1.8E-11 m/s in the K (Stress Intensity Factor) range of 0.6-9.0 MPa m~(1/2), and that of the accelerated test (60℃, 95% RHS, filled with NaCl mist) around 1.0E-10 to 3.5E-9 m/s in the K range of 0.5-30 MPa m~(1/2). The SCC propagation rates under both natural and accelerated conditions were independent of K. The lifetime of sealability estimated from 1/5 scale models was longer than that from the small bending test specimens and has a safety margin as a structure.