高低温水合流部の熱疲労特性の検討

抄録

Thermal fatigue cracking may initiate at a tee pipe where high and low temperature fluids flow in. The mixing flow causes thermal stress fluctuation at pipe inner surface. The change in fatigue life due to variable strain around hot spot, which was heated by the hot flow from the branch pipe, were investigated experimentally. The variable strain at the pipe inner surface was obtained by thermal hydraulics tests and finite element analysis. Strain-controlled fatigue tests were conducted using stainless steel specimen and the obtained strain. The minimum accumulated fatigue damage calculated by Miner's rule and rain-flow counting method was 0.18. It showed that the Miner's rule did not always evaluate the fatigue life conservatively. Since the strain around hot spot had the periodic large fluctuations, the loading sequence of periodic overload reduced the fatigue life. The accumulated fatigue damage of strain inside the hot spot was larger than those outside the hot spot and at the position of maximum stress fluctuation, because the strain inside the hot spot had the load sequence of the periodic tensile overload.