RESIDUAL STRESS EVALUATION FOR J-WELDED JOINTS OF REACTOR PRESSURE VESSEL HEAD PENETRATIONS

摘要

Welding residual stress analysis was conducted for J-welded joints of peripheral head penetrations to verify the reliability of PWR reactor pressure vessels. In the process of this analysis, 3-D thermo-elasto-plastic analysis by FEM was used. Welding process was simplified to one-pass weld. Welding temperature at the inside surface of a pipe was measured for mock-ups, and the residual stress was measured using the strain gauge method. The measured values of the peak temperature and the transient temperature in the process of cooling down almost corresponded to the analytical results. Those of the residual stress were also nearly equal to them. By these correspondences between the analyses and the measurements, the reliability of the simplified analysis was confirmed. The peak temperature appeared near the middle point between the root and toe of the weld and showed at the downhill side of the penetration weld. On the uphill side of the welds, high tensile residual stress at the inside surface of a pipe appeared under the toe. On the downhill side of the welds, however, it appeared under the root. There was a small difference between the peak residual stress at the uphill side and that at the downhill side. Additionally, the residual stress after hydrostatic test condition and that in operated condition were continuously analyzed by using the residual stress after welding. Welding residual stress became lower level after the high internal pressure of hydrostatic test though it appeared higher level after welding. In operating condition after hydrostatic test condition, the value of the residual stress went up to near that after welding. Based onthese results, both the level and trend of the residual stress for J-welded joints of reactor pressure vessel head penetrations were discussed.