Static and Dynamic J-R Tests for LBB Design Application of Ferritic Piping Materials

Dynamic J-R tests for Leak-Before-Break (LBB) design, when rapid loading is applied, have traditionally been performed using Direct Current Potential Drop (DCPD) as the measuring method of crack extension length. However, for ferritic steel, it is difficult to determine the crack initiation point due to the pulse drop from the ferromagnetic phenomenon at the initial stage of the test. Recently, a normalization method using only load and load line displacement curves was proposed and used as a standard dynamic J-R test procedure in ASTM E1820. To compare dynamic J-R curves obtained by the two different test methods, tested results using DCPD was reanalyzed in accordance with the normalization method. In the normalization method, physical crack extension length is restricted to the lesser of 4mm or 15% of the initial uncracked ligament to minimize curve-fitting errors. However, in some of the DCPD data, the results for the specimen contained physical crack lengths that propagated beyond 4mm. Actually, without ductility information for the tested materials, the possibility of violating the physical crack extension restriction for normalization for a first test specimen is high. This paper evaluates the effect of physical crack extension length on the reliability of dynamic J-R properties for LBB design of reactor coolant piping materials for Korean Standard Nuclear Power Plants. The J-R properties between dynamic and static loading are also compared.