In ASME Code Sec. III, the value of the reference nil-ductility temperature RTEDT has an important significance to determine the result of the fracture mechanics evaluation. While in the standard ...both the drop-weight test and Charpy impact test are required to determine the RTNDT, in practice it is normally determined only by the nil-ductility transition temperature (TEDT) obtained by the drop-weight test. The causes of data scatter in TNDT were investigated to establish appropriate conditions of crack-starter bead welding. Drop-weight tests were carried' out for nuclear vessel steels by changing welding conditions to examine the effects of welding amperage and shapes of welding table on TNDT. The results show that the preparation of crack-starter bead by small welding amperage should not be allowed, because it makes the measured TNDT non-conservative, and that it is important to use a welding table which increases the cooling rate of specimen. Furthermore, the authors proposed methods for estimating TNDT of nuclear vessel steels by using Charpy transition temperatures.
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