Fracture Characteristics of Cryogenic Steel Using Weibull Stress Analysis

The standardized three-point bending CTOD test as a fracture toughness test of materials has established a system in which the safety evaluation of brittle fracture of welded steel structures can be reasonably handled from the viewpoint of design, manufacture, and inspection. However, the evaluation system, which has been applied to the design, has been thoroughly examined for its validity by various experiments, analysis, and various problems have been found as a result of the application to the thick and high strength steel sheet. In particular, the concept that the failure limit evaluated by three-point bending CTOD is the same in the real structural members has been applied to the design. However, experimental and analytical results have been reported that the CTOD results do not satisfy the mechanical parameters that govern the fracture limit of cracked members. In this study, evaluated the suitability of 9% Ni steel as the inner tank material of LNG storage tank using weibull stress. For this purpose, we calculated the weibull stress from the CTOD test and predicted the failure stress and load of the real structure in consideration of the restraining effect. Key words: 9%Ni steel, Failure assessment diagram, Brittle fracture, Weibull stress, CTOD(crack tip opening displacement)