Issue34

M. Kikuchi et alii, Frattura ed Integrità Strutturale, 34 (2015) 318-325; DOI: 10.3221/IGF-ESIS.34.34 323 (a) Case 1 (b) Case 2 (c) Case 3 Figure 7 : Crack growth path in experiment and numeircal simulation. (a) (b) Figure 8 : FEM model of phase bourdary. Figure 9 : Crack growth in the phase boudary. (a) Crack path (b) Detail in phase boundary. S TRESS CORROSION CRACKING IN HOT LEG OF NUCLEAR PLANT DUE TO WELDING THERMAL STRESS tress corrosion cracking (SCC) frequently occurs in nuclear plant by welding thermal residual stress. Fig. 10 shows half of hot leg of a pipe at nuclear pressure vessel. It is welded to pressure vessel using several kinds of welding metals. Fig. 10 shows circumferentioal residual stress field by welding, which is obtained by numerical welding simulation. Residual stress field is generated in the cross section of hot leg, which triggers the crack initiation and growth by stress corrosion. Detailed cross section of this hot leg is shown in Fig.11. Hot leg is made of three materials. They are low carbon steel, stainless steel and Ni-based alloy. Material constants of them are shown in Tab. 3. Crack growth rate by stress corrosion is expressed by Eq. (6), where  and  are material constants [15], and are shown in Tab. 2. SCC does not occur in law carbon steel and stainless steel, and occurs only in Ni-based alloy.   / eq da dt K    (6) Initial crack is assumed in Ni-based alloy, in green area in Fig.11, and crack growth simulation is conducted. Figs. 12 (a)- (e) show crack growing processes. Initial crack is located inside of hot leg pipe, where residual hoop stress is very large. This initial carck grows gradually and goes near to phase boundary between low carbon steel and stainless steel. It terminates at the phase boundary, and crack continues growing inside Ni-based alloy. After 30 years, crack grows nearly S