2025 Volume 74 Issue 11 Pages 216-221
Surface-softened clad steel （SCS） was developed to achieve both high strength and high resistance to liquid ammonia stress corrosion cracking （SCC）, and SCS plates with tensile strength （TS） of 600 MPa were applied to two ammonia tanks more than 30 years ago. In order to grasp the long-term SCC resistance, the open inspection results were analyzed. During 30 years of service, one of the SCS plate tanks had no crack, and only six crack incidents were detected cumulatively in the other tank. Compared with the conventional TS600 MPa steel plate tank, SCC of the SCS plate tanks was remarkably suppressed, suggesting that the SCS plate tank has excellent long-term SCC resistance. The cracks in the SCS plates tanks were only in the welded parts, as in the same case of TS440 MPa SLA325A commonly applied to liquid ammonia tanks. It can be said that the TS600 MPa SCS plate tank has high resistance to liquid ammonia SCC equivalent to the TS440 MPa SLA325A plate tank.
