STUDY ON PREVENTION OF STRESS CORROSION CRACKING OF THE CANISTER FOR TRANSPORT AND STORAGE

In the long-term operation of austenitic stainless steel canister, the possibility of stress corrosion cracking (SCC) by chloride, are beginning to be pointed out ?1??2??3?. As measures to prevent this SCC, there are ways to convert compression stress from tensile stress represented by the welding part. Here, it is clarified that zirconia peening process or ball burnishing process can prevent SCC by using laser welding specimens of SUS304L or SUS316L stainless steel. Compressive stress layer where the ball burnishing or zirconia peening methods were applied is about 800μm and 1500μm respectively. Those depths were almost the same as the depths of hardness change. On the other hand, depths that metallurgical structures change by work hardening were 60 percent of those. To evaluate the stability of the compressive residual stress layer which is granted by peening or the like, we measured the residual stress change with adding tensile loading by X ray diffraction method. The compressive residual stress was kept compression state until base metal yield. SCC tests were carried out with boiling aqueous magnesium chloride solution in order to evaluate the processed surface performance. SCC was observed in the as welded specimen and grinded specimen. But, compressed materials by zirconia peening or burnishing did not show any SCC. In long-term use, effect of pitting corrosion was also a big concern. But, the predicted maximum pitting depth on 60 years design life is shallower than that of compressive stress layers obtained by burnishing or zirconia peening. So, long time SCC prevention by these methods can be expected.